Microbiology of Commercially Sterile and Shelf-Stable Products

6/30/05

MICROBIOLOGY OF THERMALLY PROCESSED

COMMERCIALLY STERILE AND SHELF-STABLE MEAT
AND POULTRY PRODUCTS
To understand the microbiology of thermally processed commercially sterile and
shelf-stable meat and poultry products you must first be familiar with the
microbiology of meat and poultry, as well as some basics of processed food
microbiology in general. In this section you will learn about microorganisms of
significance in thermally processed commercially sterile and shelf-stable
products, the sources of these microorganisms, the conditions affecting their
growth and inactivation, and the specific microbiology of acidified and low-acid
“canned” (commercially sterile) foods. You will learn more about the specific
microbiology of other shelf-stable meat and poultry products such as dry and
acidified/fermented products in the section on the Microbiology of Shelf-Stable
Dried Meats.

The objectives of this section are for you to be able to:

1. Recognize pathogens of concern for thermally processed commercially

sterile and shelf-stable products and distinguish them from spoilage
organisms.
2. Identify conditions affecting microbial growth and related control methods.
3. Identify causes of canned food spoilage.

Introduction to the Microbiology of Food Processing

All raw foods normally contain microorganisms that will eventually cause spoilage
unless they are controlled or destroyed. Food preservation is a competition
between the human species and microorganisms – we attempt to preserve the
food, the microorganisms attempt to destroy it (by breaking down the food for its
own consumption) in order to survive. Many of the thousands of microorganisms
that have been discovered and identified perform some useful function. Without
microorganisms, we would not have some of the tasty foods we enjoy, such as
breads, cheese, wine, beer, sauerkraut and other fermented foods, including
many sausages. Vanilla, olives, tea and chocolate are other products that
include a microbial fermentation step. In addition, these microorganisms are
needed to make products useful to industry and medicine, such as enzymes,
antibiotics, glycerol and other alcohols. Still other types of microorganisms have
the ability to break down organic matter and return it to the earth in a recycling
process to form food for plants, which in turn provide food for animals. Without
such microorganisms, the earth would accumulate dead animals, leaves and
other non-decayed matter – all of which would have eliminated life on earth long
ago.

5
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

However, it is also true that most diseases of humans, animals or plants are
caused by specific microorganisms. The microorganisms that can cause illness
are known as pathogens. The pathogen, or the substances it produces, must
invade the human, animal or plant body to cause illness. Fortunately,
comparatively few of the tens of thousands of known microorganisms are harmful
to humans. While many diseases can be transmitted from person to person or
from animals to humans, only a few can be transmitted through foods. Although
it is becoming recognized that the vast majority of cases of food borne illnesses
are caused by viruses such as hepatitis A and noroviruses (67% of all cases of food
borne illness, according to one analysis), bacterial agents, such as Salmonella and
Campylobacter, are most frequently identified as the cause of illness because we
have a much greater understanding of how to isolate and identify them.

Significant Microorganisms in Food Processing

There are many different ways to classify and group microorganisms, including
groupings based on microscopic appearance, the materials they can use as
foods, the byproducts resulting from the breakdown of these foods, their
tolerance to oxygen, their growth temperatures, and their resistance to such
destructive agents as heat and chemicals. The microorganisms of primary
concern to the food processor are generally molds, yeasts and bacteria, because
they can grow in the food and cause spoilage. Processors are also concerned
about viruses and parasites in foods, although they are not capable of growing in
the food and do not cause spoilage. Bacteria, viruses and parasites are of
particular concern because a number of them cause illness. A brief review of the
significant groups of microorganisms in food processing follows.

►Molds

Molds exhibit some of the characteristics of the higher plants. They are multiple
cell organisms forming tubular filaments. Molds demonstrate branching and
reproduce by means of fruiting bodies, called spores, which are borne in or on
aerial structures. Their mycelia, or intertwined filaments, may resemble roots.
They are many times larger than bacteria and somewhat longer than yeasts.

Molds are widely distributed in nature, both in the soil and in the dust carried by
air. Under suitable conditions of moisture, air and temperature, molds will grow
on almost any food. The black or green discoloration that appears on moldy
bread is familiar evidence of such growth. Molds are also able to survive on a
wide variety of substances not normally thought suitable for the support of life.
These include concentrated solutions of some acids and water containing minute
quantities of certain salts, as well as on building structures. Molds grow readily
on the walls and ceilings of buildings where there is high humidity and

6
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

considerable moisture condensation. Mold growth can even occur in

refrigerators, because molds are much more tolerant to cold than to heat. Molds
can grow at reduced water activities (aw) and can be a problem in improperly
processed dry and semi-dry fermented products, as discussed later.

Molds are capable of consuming acids, thereby raising the pH of products. Their
growth in foods has, on very rare occasions (and never in meat or poultry
products), removed the acid conditions that inhibit growth of Clostridium
botulinum, a food borne pathogen discussed later in this section.

Most molds have little heat resistance and cannot survive the thermal processes
for low-acid canned foods. Some molds produce a type of spore (ascospore)
that is more resistant to heat, but these spores are much less resistant than the
spores that are the target of processes for low-acid and acidified canned foods;
these heat-resistant molds have not caused problems in meat and poultry
products. Therefore, molds are present in canned meat and poultry products
only as a result of gross under-processing or as a post-processing contaminant.
Since molds must have oxygen to grow, only slight growth can occur unless the
food container has an opening to the outside environment.

Mold growth in thermally processed commercially sterile and shelf-stable foods

has to date not been shown to present a public health problem. In fact, mold is
used in the ripening process of some sausages, as will be discussed in other
sections.

►Yeasts

Another microorganism of importance to food preservation/spoilage is yeast.

Yeasts are single cell, microscopic living bodies, usually egg-shaped. They are
smaller than molds, but larger than bacteria. Their greatest thickness is about
1/2,000 of an inch. Yeasts reproduce mainly by budding. A small bud forms on
the parent yeast cell and gradually enlarges and breaks off into another yeast
cell. A few varieties reproduce by forming spores within a special cell; later these
spores may form new yeast cells.

Yeasts are widely found in nature and are particularly associated with liquid
foods containing sugars and acids. They are quite adaptive to adverse
conditions such as acidity and dehydration. Like molds, yeasts are more tolerant
to cold than to heat. Compared to bacterial spores, yeasts and their spores
possess little resistance to heat. Most yeast forms are destroyed on heating to
170ºF (77ºC). Spoilage may result from the presence of yeast in canned food,
but if this happens, gross under-processing or leakage must be suspected.
Usually the growth of yeasts results in the production of alcohol and large

7
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

amounts of carbon dioxide gas, which swells the container.

Yeast growth in processed foods does not present a public health problem.

►Viruses

Virus particles are so small they cannot be seen by the standard light
microscopes used in laboratories – a special electron microscope is needed to
see these microorganisms. A virus particle is composed of either RNA or DNA
enclosed in a coat of protein, sometimes with an outer envelope containing lipids
(fats). (Deoxyribonucleic acid (DNA) is a nucleic acid which carries genetic
instructions for the biological development of all cellular forms of life and many
viruses. Ribonucleic acid (RNA) transmits genetic information from DNA to
proteins, and carries the genetic instructions for many viruses.) Viruses lack the
enzymes and other components needed to replicate. Thus, viruses cannot
multiply in food – they can only replicate themselves in suitable living host cells.
Viruses transmitted by food are produced in the human body and shed in the
feces. Of particular concern for foods are the hepatitis viruses and noroviruses.
These latter viruses have been mentioned in many news stories in recent years
for causing large outbreaks of vomiting illnesses at large gatherings and on
cruise ships. Viruses get into food through contaminated water and infected food
handlers with poor hygienic practices.

Viruses are not heat resistant, with most having resistance similar to non-spore
forming bacteria (see below). Hepatitis A virus is somewhat more resistant, but
is still inactivated at 185°F (85°C). Avian influenza virus, which can infect
chickens, turkeys, pheasants, quail, ducks, geese, and guinea fowl, as well as a
wide variety of other birds, has been known to infect humans, but it is not
transmitted through foods, nor is exotic Newcastle disease virus, which also
causes a highly contagious poultry disease. Heating to at least to 161.6°F (72°C)
internal temperature is considered adequate to inactivate both these viruses.

The Human Immunodeficiency Virus (HIV) which causes the disease AIDS
(Acquired Immune Deficiency Syndrome) is a severe public health problem. AIDS
has never been shown to be transmitted by food or drink. Individuals who are
known to be infected with the virus can handle food safely if they observe basic
sanitation precautions for food handling and take care to avoid injury when
preparing food. As with any food handler, should an injury occur, food
contaminated with blood should be discarded for aesthetic as well as safety
reasons. Employees should be restricted from handling food if they have evidence
of infection or illness that would otherwise require that they not handle food.

Viruses are not a concern in thermally processed commercially sterile and shelf-
stable meat and poultry products.

8
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

►Parasites

The parasites of concern in the production of meat and poultry products include
worms and protozoa. Some of them are large enough to be seen with the naked
eye, whereas others are microscopic. Parasites cannot multiply in food, only in a
host cell, and they are not heat resistant.

Parasitic worms of public health importance are the beef and pork tapeworms
(Taenia saginata and Taenia solium, respectively) and the roundworm that
causes trichinosis (Trichinella spiralis, also referred to as trichinae) found in pork.
These small cysticerci (refered to as Cysticercus cellulosae) are approximately 6-
18mm wide by 4 - 6mm in length when found in the muscles or subcutaneous
tissues (the normal sites for the larvae of this parasite). The cysticerci may
however be found in other tissues, such as those of the central nervous system,
where they may grow much larger up to several cm in diameter.
Muscle and organs of animals with severe tapeworm infection are usually visually
detected by government inspection personnel or by plant employees through
evidence of the immature stages (larval stage in a cyst known as a cysticercus)
of tapeworms, which are 6- 18 mm wide by 4 – 6 mm in length when found in the
muscles. Such product cannot be further processed for human consumption.
When the cysts are less severe or evident, infected meat may enter the human
food chain, however illness will not occur if meat is properly cooked. Humans
consuming undercooked meat infected with these tapeworms become ill with
taeniasis generally after the mature stages of the tapeworms, which develop from
the cysticercus, invade the intestinal tract. Most cases of infection with adult
worms are without symptoms. Some persons may experience abdominal pain,
weight loss, digestive disturbances, and possible intestinal obstruction.
Taeniasis may last many years without medical treatment. However, people can
get a more serious illness called cysticercosis by consuming food or water
contaminated with the eggs of T. solium (pork tapeworm). Worm eggs hatch and
the larvae then migrate to various parts of the body and form cysts (cysticerci).
This can be a serious or fatal disease if it involves organs such as the central
nervous system, heart, or eyes. Symptoms may vary depending on the organ or
organ system involved. For example, an individual with cysticercocis involving
the central nervous system (neurocysticercosis) may exhibit neurological
symptoms such as psychiatric problems or epileptic seizures. Death is common.

Trichinella spiralis is an intestinal worm that produces larvae that migrate to and
encyst in muscles of a number of animals, particularly swine. Humans
consuming infected pork that is undercooked get ill from the cysts, which then
live in the muscles of the human hosts. The first symptoms are nausea,
diarrhea, vomiting, fever, and abdominal pain, followed by headaches, eye
swelling, aching joints and muscles, weakness, and itchy skin. In severe

9
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

infections, persons may experience difficulty with coordination and have heart
and breathing problems. Death may occur in severe cases.

Parasitic protozoa of concern in meat processing include Cryptosporidium

parvum and Toxoplasma gondii. Cryptosporidium is typically transmitted to
humans from fecal material of animals, primarily cattle, via contaminated water or
occasionally, food. The organism is destroyed by boiling water. Toxoplasma
gondii is carried by cats but can infect many warm-blooded animals. A form
known as the oocyst is shed and can sporulate and survive in soil and other
environments for extended times; the sporulated oocyst is infectious to all warm-
blooded hosts. When ingested, the sporulated oocysts go through several forms,
eventually forming cysts in tissue such as muscle. These cysts are infective if
ingested. Toxoplasma can cross the placenta and affect the fetus, resulting in
blindness and more serious effects in the brain.

Parasites are readily destroyed at cooking temperature and are not a major
concern in thermally processed commercially sterile meat and poultry products
since they are subjected to temperatures well in excess of what is needed to
destroy parasites. Parasites are a concern with respect to shelf-stable products
that are not cooked. For example, trichinae are a concern with respect to shelf-
stable products, such as dried sausages, containing pork. We’ll discuss this
further in the module for the microbiology of shelf-stable dried meats.

►Bacteria

Bacteria are the most important and troublesome of all the microorganisms for
the food processor. Bacteria are single-celled living bodies so small that
individually they can be seen only with the aid of a microscope. They are among
the smallest living creatures known. The cells of bacteria vary in length from
1/25,000 to 1/1,000 of an inch. The number of these tiny microorganisms that
could be placed on the head of a pin would equal the population of New York
City! Viewed with a microscope, bacteria appear in several shapes or forms, but
are primarily either round in shape (called “cocci”) or rod-shaped (called “rods”).

Reproduction of bacterial cells

Bacteria reproduce by division, which microbiologists call fission. When a

bacterial cell is ready to divide, the cell material gradually increases until its
volume is almost doubled. The cocci shapes become oval while rod shapes
stretch to nearly twice their length. The cell then constricts in the middle. This
constriction deepens until the cell contents are held in two distinct compartments
separated by a wall. These two compartments finally separate to form two new

10
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

cells, which are duplicates of the former cell and each other. Since the
reproduction of bacteria increases the numbers, it is often referred to as “growth.”

Experiments conducted to determine the growth rate of bacteria under favorable

conditions have found that each cell divides, on the average, about every 20 or
30 minutes. At this rate of cell division, each single cell will produce four cells at
the end of the first hour. At the end of two hours, each cell will have produced 16
new cells. After 15 hours, each parent cell will have produced 1,000,000,000
(one billion) cells identical to the original. For example, if there were 75,000
bacteria per square inch on a conveyor belt, by the end of one hour there could
be 300,000 bacteria per square inch of that belt. At the end of a three-hour shift,
the bacteria count per square inch of belt surface could be 4,800,000.

Bacterial growth becomes limited without a constant supply of available fresh

food. Also, large numbers of bacteria result in an accumulation of substances
that are byproducts of bacterial growth and that also inhibit growth. With
cessation of growth due to pollution of their environment, the cells may die.
However, if the microorganism is a type that forms resistant but dormant spores,
these cells can remain alive under conditions that kill other cells.

Sporeforming and non-sporeforming bacteria

Bacteria can be divided into two groups based on their ability or inability to form
spores. Practically all of the round-shaped bacteria (cocci) and many of the rod-
shaped bacteria cannot form spores; thus they are classified as non-
sporeformers. However, a number of the rod-shaped bacteria have the ability to
produce a spore within the cell (endospore). Spores are a dormant stage in the
normal growth cycle of these organisms. They have the ability to survive a wide
range of unfavorable conditions. The primary function of most spores is to
ensure the survival of the organism through periods of environmental stress.
Spores have been compared to plant seeds because they will germinate and
grow when conditions are suitable. The major sporeforming bacteria are species
of Clostridium and Bacillus. Cells of non-sporeformers and the cells of
sporeformers that have not formed spores are referred to as “vegetative cells.”
These cells generally have little resistance to heat, drying and other unfavorable
conditions.

When formed in yeasts and molds, spores represent reproductive bodies, but
bacterial spores are a resting stage in the growth cycle of these organisms.
When a bacterial spore germinates, it is simply the same organism continuing its
growth process.

11
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Resistance of spores to the environment

In general, bacterial spores are extremely resistant to heat, cold and chemical
agents. Some bacterial spores can survive in boiling water – 212ºF (100ºC) – for
more than 16 hours. The same organisms in the vegetative state and the non-
sporeforming bacteria will not survive heating in boiling water.

As a general rule, spores that successfully resist heat are also highly resistant to
destruction by chemicals. There are bacterial spores that can survive more than
three hours in sanitizing solutions normally used in a food processing plant. On
the other hand, vegetative cells (non-sporeforming bacteria and the vegetative
cell form of sporeformers) are readily destroyed by these sanitizing agents. The
purpose of sanitizing is not to sterilize surfaces (to remove all bacteria), so the
survival of spores under appropriate sanitation practices is not a concern – they
will be present in low numbers and will be inactivated or controlled in the final
product.

Bacterial hazards of concern in meat and poultry

Of the microbiological hazards of concern in meat and poultry, the most

important are bacteria. Illness from meat and poultry is primarily caused by
bacterial pathogens. The pathogens that are most likely to be found in livestock
(cattle, sheep, and swine) and poultry (chicken and turkey) include Salmonella,
Campylobacter, and Listeria monocytogenes. Listeria monocytogenes also is
widespread in the environment. Escherichia coli is also found in livestock and
poultry, but most strains are not pathogenic; the pathogenic E. coli of primary
concern is known as E. coli O157:H7 and is found in beef. (Although the
organism has occasionally been found in chickens and pigs, it has not been
known to cause illness from those animals.) Yersinia enterocolitica is a pathogen
most commonly associated with pork; only certain serotypes (strains) are
pathogenic. Clostridium perfringens can also be found in meat and poultry; the
spores may survive cooking and grow to high numbers in foods due to
temperature abuse. Clostridium botulinum is rare in meats. When present, it is
there in very low numbers (estimates are 0.1 spore to 7 spores per kg meat).
Bacillus cereus is another sporeformer of concern in meat and poultry products,
especially those containing spices, which is a common source of the spores.

All of these pathogens have been implicated in food borne disease outbreaks
associated with the consumption of meat and poultry products in which these
hazards were not properly controlled. Proper cooking or thermal processing,
fermentation, cooling, and storage of food can destroy and/or prevent growth of
these bacteria.

12
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Sources of Microorganisms
Raw materials and ingredients are the primary sources of microorganisms that
must be addressed in the production of thermally processed commercially sterile
and shelf-stable products. Although muscle tissue is generally considered to be
sterile, raw meat and poultry become contaminated during slaughter and further
processing. The ultimate source for pathogens in raw meat and poultry is
apparently-healthy animals that may shed these bacteria in their feces. While
dressing the carcasses during the slaughter process, these bacteria may be
transferred from the hide, skin, feathers, gastrointestinal tract and other offal to
the carcass, causing contamination. This is also a major source of spoilage
microorganisms.

Soil or water can be a common source of food borne microorganisms and

spores. Vegetables become contaminated during production, with those that
grow close to or through the soil usually having high numbers of bacteria and
bacterial spores, including spores of C. botulinum. Contaminated water used for
irrigation has also been a source of pathogens on vegetables. Dried herbs and
spices can be a primary source of sporeformers, since the spores will survive for
extended times in the dehydrated product. Soy and milk protein ingredients can
also be sources of spores.

Contamination can also come from the processing environment. Utensils such
as knives used in slaughter and fabrication, workers hands and gloves,
equipment, and occasionally aerosols with dust and other particles carrying
microorganisms can all contribute to the microbial load of products.
Contaminants may be present on containers and other packaging materials,
although this is generally not a likely source of pathogens. Proper sanitation of
the environment and protecting containers from environmental contamination can
prevent these from being major sources of contamination such that they will
negatively impact thermally processed commercially sterile and shelf-stable
products.

Conditions Affecting Microbial Growth

The following information focuses on bacteria, since we are most concerned with
bacterial pathogens; however, much of it is applicable to yeasts and molds as
well. It is not applicable to parasites and viruses, since they do not grow in food.

13
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

►Nutrient Requirements

A suitable food supply is the most important condition affecting growth of

bacteria. Every living cell requires certain nutrients to multiply. These include
solutions of sugars or other carbohydrates, proteins and small amounts of other
materials such as phosphates, chlorides and calcium. If the food supply is
removed, bacteria will not multiply.

►Moisture Requirements

The concentration of moisture and its availability in a food (referred to as water

activity, or aw) are important factors to prevent microbial growth. The bacterial
cell has no mouth, and therefore its food must be in a soluble form to enter the
cell through the cell wall. Without sufficient available moisture, the inflow of food
and the outflow of food residues and cell body fluids would be impossible. Later
we will discuss how bacterial growth can be prevented by controlling the amount
of moisture available to the bacteria.

►Oxygen Requirements

Some bacteria – called aerobes – require free oxygen in order to survive. For
others, called anaerobes, the reverse is the case – the smallest quantity of free
oxygen prevents their growth. The majority of bacteria – called facultative
anaerobes – are neither strict aerobes nor strict anaerobes, but can tolerate to
some degree either the presence or absence of oxygen.

►pH Requirements

The term pH designates the acidity or alkalinity of an aqueous solution.

Scientifically, pH is the negative logarithm of the hydrogen ion concentration.
The pH scale ranges from 0 to 14, with pH 7 being neutral. Numbers smaller
than 7 indicate an increase in hydrogen ion (more acid) and numbers greater
than 7 indicate a decrease in hydrogen ion concentration (more basic, or
alkaline). All bacteria have an optimum (most favorable) pH range for growth
(generally around neutral pH), as well as a minimum below which the organism
will not grow (and where the organism may die) and a maximum above which it
cannot grow. The pH of foods can be adjusted to help control microbial growth,
as will be described later.

14
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

►Temperature Requirements

As with pH, all bacteria have an optimum temperature range for growth.
Temperatures below and above the optimum for each group adversely affect the
growth of the organism; all bacteria have a minimum and a maximum
temperature below or above which the organism cannot grow. Bacterial groups
bear names that indicate their relationships to temperature – psychrophile,
psychrotroph, mesophile, thermophile.

The psychrophilic and psychrotrophic group

The terms psychrophile and psychrotroph are sometimes used interchangeably,

but the groups are distinguished by their optimum growth temperatures and
temperature ranges. Both psychrophiles and psychrotrophs grow over the
temperature range of subzero to 68°F (20°C). True psychrophilic bacteria
(“psychro” for “cold,” “phile” for “loving”) have an optimum temperature of 59°F
(15°C) and cannot grow above 77°F (25°C). Psychrotrophic bacteria generally
grow best at around 77°F (25ºC), or even mesophilic temperatures (see below),
but can grow slowly in or on food at refrigerator temperatures (around 40ºF
(4ºC)). These organisms are primarily responsible for spoilage of refrigerated
foods. L. monocytogenes and some strains of C. botulinum (C. botulinum type E
and non-proteolytic strains of type B and F) are considered to be psychrotrophs.
None of these bacteria – except perhaps the strains of C. botulinum – is of
concern to low-acid or acidified canned foods.

The mesophilic group

Mesophilic bacteria grow best at temperatures of 86ºF to 104°F (30ºC to 40°C)

(the normal range of warehouse temperatures, depending on geographic
locations), although some mesophiles grow well at higher temperatures such as
116ºF (46.7ºC). All of the bacteria that affect food safety grow within this
mesophilic temperature range, although some may be considered psychrotrophic
as well. The sporeforming organism C. botulinum is a member of this group,
although some strains are considered psychrotrophs (see above).

The thermophilic group

Thermophiles (“thermo” for heat, “phile” for loving) are bacteria that grow at high
temperatures. Thermophilic bacteria are found in soil, manure, compost piles,
and even hot springs. Many are sporeforming bacteria and are divided into two
groups based on the temperature at which the spores will germinate and grow. If
the spores will not germinate and grow below 122ºF (50ºC), the bacteria are

15
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

called obligate thermophiles, i.e., the high growth temperature is an absolute

requirement. If growth occurs at thermophilic temperatures of 122º to 150ºF
(50ºC to 66ºC) and at lower temperatures – e.g., about 100ºF (38ºC) – the
bacteria are called facultative thermophiles, meaning they have the ability to
grow at both temperature ranges.

Some of the obligate thermophiles can grow at temperatures up to 170ºF (77ºC).

Laboratory tests have indicated that the spores of these bacteria are so heat-
resistant that they can survive for more than 60 minutes at temperatures of 250ºF
(121ºC). Thermophilic bacteria are not pathogenic and do not produce toxins
during spoilage of foods; therefore, they do not affect food safety.

►Interaction of Factors

The level of a single growth-limiting factor to inhibit a microorganism is usually

determined under conditions under which other factors that could influence
growth are optimal. When other factors are not optimal, the organism will not be
able to grow at the minimum or maximum level of another factor. For example,
when the water activity is lower, the pH range at which an organism can grow is
more limited. When the pH is lower, the water activity that limits growth will be
higher. The presence of preservatives can affect the pH at which an organism
grows; growth may take longer at lower temperatures when preservatives are
present. With that in mind, let’s look at some of the control methods for
microorganisms in foods.

Control Methods for Microorganisms

►Control of Bacteria by Temperature

Bacterial growth can be controlled by keeping food at temperatures below the

minimum or above the maximum for the organism to grow. Thus, refrigeration,
freezing and hot holding can be used to control growth. However, the most
effective use of temperature to control microorganisms is to kill them with heat.
The amount of heat needed to inactivate the microorganisms of concern will be
dependent on the specific microorganism (the species and whether or not it is in
the spore form), the number of microorganisms to be inactivated, and the food
product in which the microorganism is heated (and factors of the food such as its
pH, aw, the presence of preservatives such as nitrite).

The thermal resistance of microorganisms is generally expressed using D- and z-

values. The D-value is the time in minutes at a constant temperature to destroy
90% (or 1 log) of the organism present; the z-value is the number of degrees
between a 10-fold change (1 log cycle) in an organism’s resistance. For

16
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

example, if an organism has a D-value of 5 minutes at 140°F and a z-value of

10°F, then the D-value at 130°F will be 50 minutes and the D-value at 150°F will
be 0.5 minutes. If there are <100,000 microorganisms present in a sample, then
a process that delivered a 5-D reduction (also called a 5-log reduction) to the
sample would result in <1 microorganism remaining. We will refer to this log-
reduction concept again in the section on thermal processing of commercially
sterile products and in the section on the microbiology of shelf-stable dried
meats.

In general, low-acid commercially sterile products will require high temperatures

that are achieved by processing under pressure to inactivate the organisms of
concern. Acidified meat and poultry products can be processed at lower
temperatures, since only vegetative cells must be inactivated; the pH prevents
germination and outgrowth of the spores. In canned cured products, the
presence of nitrite and salt reduces the amount of heat needed to achieve
commercial sterility (heat kills the vegetative cells of pathogens; salt and nitrite
prevent germination and outgrowth of spores). In most canned products it is not
the pathogen of concern that determines the amount of heat needed but rather
the spoilage microorganisms, which are more heat resistant than the pathogens.
If these organisms are not inactivated, the product will not be shelf-stable. In
most instances, this provides a wide margin of safety with respect to survival of
pathogens in the product.

►Control of Bacteria by pH

As noted above, microorganisms can be controlled by reducing the pH below the

minimum for growth of the organism. An “acidified low acid product” is defined
by FSIS as a canned product which has been formulated or treated so that every
component of the finished product has a pH of 4.6 or lower within 24 hours after
the completion of the thermal process unless data are available from the
establishment’s processing authority demonstrating that a longer time period is
safe. Proper acidification is necessary to prevent the growth of C. botulinum.
Unlike processes for low-acid foods that destroy C. botulinum spores, processes
for acidified foods depend upon the pH of the food to prevent this organism from
growing. The final equilibrium pH of an acidified food must be 4.6 or lower to
prevent growth of C. botulinum However, since some microorganisms can cause
illness at very low levels (e.g., Escherichia coli O157:H7), preventing growth
alone will not provide a safe product. Reduced pH can be combined with other
factors to control the pathogens of concern. For example, a reduced pH,
combined with a mild heat treatment, is used to achieve commercial sterility in
acidified meat and poultry products such as pasta sauces containing meat. The
role of pH in conjunction with other factors in the production of
acidified/fermented meat and poultry products will be covered in the sections on
Principles of Preservation of Shelf-Stable Dried Meat Products and the

17
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Microbiology of Shelf-Stable Dried Meats. The pH values for representative

canned meat and poultry products are shown in Table 1.

Table 1 – pH values of representative canned meat and poultry products

Food pH

Beans with wieners 5.7

Beef chili 5.6
Beef stew 5.4-5.9
Chicken and dumplings 6.4
Chorizos 5.2
Corned beef 6.2
Corned beef hash 5.0-5.7
Ham 6.0-6.5
Spaghetti and meatballs 5.0
Spaghetti sauce with beef 4.2
Sloppy Joe 4.4
Vienna sausage 6.2-6.5

Acidification procedures

To produce products with a pH of 4.6 or less, acidification must be properly

carried out. While there are several methods to obtain properly acidified foods,
one commonly used with meat products is direct batch acidification. Ingredients
are mixed in a kettle, and acid or, more commonly an acid food, is added directly
to the batch. (An elevated temperature may improve the rate of acid penetration
into solid particles.) The pH of the batch is checked before the material is sent
from the batch kettle to the filler. If the particle size is small enough, the product
pH will be below 4.6 at this point. With larger particles, the product may not
reach the desired pH until later; however a pH taken at this point can be used to
determine that the acidification process is under control. Another method that is
used for acidification of meat products is the addition of acidified brine, such as
with pickled pigs’ feet. Other methods will be discussed in the section on
Principles of Thermal Processing.

Determination of pH

The most important factor in the production of acidified foods is the timely
attainment and maintenance of a pH level that will inhibit the growth of
C. botulinum spores. To achieve this goal, it is necessary to measure pH.

18
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Although pH can be measured using colorimetric methods (dye solutions and pH

paper) or by titratable acidity, the recommended method for determining pH is
the electrometric method using a pH meter. The pH meter measures the
electrical potential developed between a glass and a reference electrode when
they are immersed in a solution. USDA currently requires the electrometric
method to be used any time pH is specified as a critical factor for a scheduled
process.

The sensing elements used with pH meters are called electrodes. Combination
electrodes contain both a glass and reference electrode in a single probe. They
come in a number of different sizes and conformations, which increases the
applications of this type of electrode. For example, flat-surface electrodes are
useful for measuring the surface pH of a solid sample; long, thin electrodes may
be inserted in tubes for measuring pH of small sample volumes or inserted into
the process stream for continuous monitoring of pH. Unbreakable electrodes
should be used in food processing plants to minimize the chances of
contaminating food. For best results, pH meters should be operated in
accordance with manufacturer's instructions; the manufacturer’s
recommendations should be followed for care and maintenance of all pH
electrodes.

Once the unit has been turned on and allowed to warm up, the meter should be
properly standardized (calibrated) using two buffers to cover the pH range of
interest, such as one at pH 4.0 and the other at pH 7.0. The meter should be
standardized (1) before any food pH measurements are taken and (2) at least
once an hour following that. More frequent standardization and cleaning may be
necessary with some products that contain oil, grease or fats.

The sample to be tested must be properly prepared, which is dependent on the

type of product to be evaluated. Homogeneous products, such as sauces,
require little preparation. Products that consist of solid and liquid components
should have the solid components tested separately to determine if they have
been properly acidified. One means of sample preparation is to transfer a portion
of the solid component to a screen, rinse it with a small volume of distilled water
(10-20 ml), and thoroughly blend before taking a pH. Sufficient tests must be
made to ensure that the finished equilibrium pH of the product is not higher than
4.6. These tests indicate whether the acidification process is sufficient to bring
the product to the appropriate pH.

Electrodes should be rinsed between samples and after use. The purpose of
rinsing is to prevent cross-contamination between samples that could result in
errors in pH values for products. Rinsing with distilled water is recommended.
However, if enough sample is available, rinsing with a portion of the next sample
to be measured and throwing away the rinse solution is the best way to prevent
cross-contamination. If distilled water is used, the water should be blotted – not

19
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

wiped – off the electrodes. If the electrode is rinsed with the next sample, this
step is not necessary. Electrodes should not be wiped, because wiping could
implant a charge on the electrode causing it to drift. Oil and grease from
samples may coat or clog elements; therefore, electrodes should be cleaned with
ethyl ether or acetone in accordance with the manufacturer's instructions, and the
instrument should be re-standardized frequently. If the primary use is to test high
fat/oil products, special electrodes are available.

►Control of Bacteria by Water Activity (aw)

For thousands of years people have dried fruits, meats and vegetables as a
method of preservation. It was also discovered that the addition of sugar would
allow preservation of foods such as in the production of candies and jellies. Salt
preservation of meat and fish has been extensively practiced over the ages.

As late as 1940, food microbiologists thought that the percentage of water in a

food product controlled microbial growth, but gradually they learned that it is the
availability of the water that is the most important factor influencing growth. The
measure of the availability of water in a food is made by determining the water
activity. Water activity is usually designated with the symbol “aw.”

When substances are dissolved, there is substantial reaction between the

substance and the water. A number of the molecules of the water are bound by
the molecules of the substances dissolved. All of the substances dissolved in the
water reduce the number of unattached water molecules and, in this way, reduce
the amount of water available for microbial growth. The extent to which the water
activity is lowered depends primarily on the total concentration of all dissolved
substances. Thus, if some ingredient – such as sugar, salt, etc. – is added to
food, it competes with the bacteria for available water. The water-binding
capacity of a particular dissolved ingredient influences the amount of water left
for the growth of bacteria.

Meat or poultry containing products with a water activity of 0.85 or less are not
covered by the USDA canning regulations (9 CFR 318 Subpart G (meat) and 381
Subpart X (poultry)) even if they are in hermetically sealed containers.

The aw is the ratio of the vapor pressure of a substance to the vapor pressure of
pure water, and is equal to the equilibrium relative humidity divided by 100.
Thus, aw is a fraction between 0 and 1.00, with the aw of pure water being 1.00.

A measurement of aw on a food provides information as to which types of

microorganisms are most likely to cause spoilage and how close the aw is to the
safety limits. Most bacteria, yeasts and molds will grow above a water activity of
0.95 (See Table 2), and most foods have a water activity above this level.

20
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Spores of C. botulinum are generally inhibited at an aw of about 0.93 or less.

(For more information on the effect of aw on C. botulinum, see the section on salt
under Control by Chemicals below.) Therefore if the amount of water available to
spores is decreased to a point where they are inhibited and mild heat treatment
is applied to destroy the vegetative cells, we have a method of preservation for
products whose quality is sensitive to high heat.

Table 2 – Minimum aw requirements for microorganism growth

Microorganism Minimum aw For Growth

Most molds (e.g., Aspergillus) 0.751

Most yeasts 0.882
C. botulinum3 0.93
Staphylococcus aureus4 0.85
Salmonella 0.94
Listeria monocytogenes 0.92
1
some strains – 0.61
2
some strains – 0.62
3
Proteolytic strains, 10% NaCl
4
Minimum for toxin production is higher.

Examples of foods preserved with mild heat and reduced aw are some cheese
spreads, peanut butter, syrups, jams and jellies, and many meat products. The
water activity of some common foods is shown in Table 3.

Table 3 – Water activity of some common foods

Food aw

Perishable and canned foods (including

meats, vegetables, fish and milk) 0.95-1.00
Liverwurst 0.96
Some cheese spreads 0.95
Some cheeses and cured meats 0.91-0.95
Chorizos 0.92
Many fermented sausages 0.87-0.91
Semi-moist pet food 0.83
Salami 0.82
Chocolate syrups 0.75-0.83
Jams 0.75-0.80
Peanut butter – 15% total moisture 0.70
Jerky ≤0.80

21
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

It is apparent that as far as C. botulinum is concerned, a water activity of 0.85

provides a large margin of safety. Studies with this organism show that an
accurate water activity of 0.93 plus pasteurization will give commercial sterility.
However, some questions exist about the precision or accuracy of the
instruments and methods used to determine water activity and about some
factors that control water activity. Therefore, if water activity between 0.90 and
0.93 plus pasteurization is used to control commercial sterility, data must be
obtained and records kept showing that the process yields commercial sterility.

Methods for determining aw

Several methods exist for determining the water activity of a food. One
commonly used method is an electric hygrometer with a sensor to measure
equilibrium relative humidity (ERH). As noted above, the equilibrium relative
humidity above the food in a closed container divided by 100 is a measure of the
available moisture – the water activity. The instrument was actually devised by
weathermen, and the sensors are the same as those used to measure relative
humidity in air. A dew point instrument is also commonly used to measure aw.
This instrument measures the temperature at which condensation occurs on a
cooled mirror in the headspace of the sample chamber. The aw is computed by
converting sample and mirror temperatures to vapor pressures and calculating
the ratio, which is the aw.

In determining the aw using an electric hygrometer, 30-90 minutes may be re-

quired for the water vapor (relative humidity) to reach equilibrium in the
headspace above the food in the closed container. A dew point instrument is
usually much faster – generally only 5 minutes. Generally the formulation of the
product to give the required aw is predetermined and very accurately controlled at
the time of processing. For products that have a reduced aw due to reduction in
moisture (e.g., through a drying process), following proper procedures can be
critical. Determination of aw in a laboratory is often used to verify that the
formulation and other steps that reduced product moisture were correctly carried
out and the appropriate aw was achieved. Samples of the final product should be
checked as frequently as necessary to ensure that the appropriate water activity
is being achieved.

►Control of Bacteria by Chemicals

Chemicals (often called preservatives, antimicrobial compounds, or

antimicrobials) may be added to foods to inhibit microbial growth or to kill
microorganisms. However, at normal levels of use (which must be approved by
regulatory agencies such as FDA and FSIS), most chemicals cause inhibition
rather than inactivation. Acids and their salts (e.g., lactic acid, sodium lactate),

22
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

nitrites, some phosphates, and sodium chloride (salt) are common chemicals
added to meat and poultry. In order to produce a commercially sterile or shelf-
stable product, chemicals are usually combined with other factors such as heat
or reduced aw.

Salt

For example, salt has been used to preserve meat products (i.e., salt-cured
meats). Salt, which lowers the aw, is often supplemented with other ingredients,
such as nitrites, that aid in spoilage prevention. In all cases the salt is necessary
to inhibit the growth of sporeforming bacteria, such as C. botulinum, and only
enough heat is applied to kill the non-heat resistant vegetative cells. Strains of
C. botulinum that grow in a suitable food containing 7 percent salt are known.
For example, toxin was produced in experimentally produced turkey frankfurters
with an aw of 0.956 (7% NaCl) in 12 days at 27°C (81°F). The growth of these
strains, however, is inhibited at a concentration of 10 percent, which is equivalent
to a water activity of 0.935, when all other conditions are optimum. If conditions
are not optimum for growth (e.g., low pH or temperature) then less NaCl is
required to inhibit growth. For example, growth of C. botulinum may occur at an
aw of 0.96 (6.5% NaCl) at pH 7.0, but if the pH is reduced to 5.3, growth will be
inhibited at an aw of 0.97 (5% NaCl). The actual salt content of a meat product is
not as important in inhibiting C. botulinum as the brine concentration (percent of
salt in the aqueous portion of the meat). Toxin production is inhibited at a brine
level exceeding 9.0%.

Nitrite

When direct addition of nitrite was approved for meats in 1925, it was believed
that the sole function was for color development. However, within a few years
scientific studies began to demonstrate the antimicrobial effects of this
compound. Numerous studies now document the efficacy of nitrite in inhibiting
growth and toxin production by C. botulinum in meat systems. However, studies
also determined that there was little or no effect of nitrite on bacterial growth at or
above neutral pH. In spite of large amounts of research, there is still not a
complete understanding of how nitrite controls C. botulinum in meat products.
Nevertheless, it is now recognized that nitrite inhibition is due to a combination of
factors, not nitrite alone.

►Control of Bacteria by Combinations of Factors

As has been noted above for chemicals, combinations of inhibitory factors that
individually are insufficient to control microorganisms can often be effective. This
has sometimes been referred to as the hurdles concept – if enough hurdles or

23
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

barriers are included, bacteria will not be able to overcome the hurdles and grow.
Commercially sterile, canned cured meats are preserved by thermal destruction
of vegetative cells of microorganisms, partial destruction of microbial spores and
inhibition of the surviving spores by the effects of salt, nitrite, and possibly other
additives such as ascorbate/isoascorbate.

The hurdle approach is used for many fermented meat products – curing
chemicals such as nitrite and salt, reduced aw due to drying, reduced pH due to
fermentation, and, in some cases, mild heat processes result in a safe and shelf-
stable product. This will be covered in much more depth in the sections on shelf-
stable products.

24
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Workshop: Microbiology of Commercially Sterile and Shelf-

Stable Products

The following questions are multiple-choice questions. Circle the answer(s) you
believe to be correct; some questions have more than one answer.

1. Microorganisms that can grow in food and cause spoilage include _____ .

a. viruses
b. bacteria
c. molds
d. yeasts
e. parasites

2. A psychrotrophic non-sporeforming pathogen that can grow at refrigerator

temperatures is ___.

a. Clostridium botulinum
b. Bacillus cerus
c. Clostridium perfringens
d. Listeria monocytogenes

3. Controlling microorganisms in foods can be achieved by _______ .

a. temperature
b. pH
c. acidification
d. water activity

4. The pH established to provide safety with respect to C. botulinum is ____ .

a. 4.6
b. 4.7
c. 4.8
d. 4.9

5. Spores of C. botulinum are generally inhibited at an aw of about ___or

less.

a. 0.98
b. 0.85
c. 0.93

25
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

6. Reducing the water activity of a food product to 0.85 would have the best
potential for inhibiting ________ .

a. bacteria
b. mold
c. yeast

7. Bacteria that can survive adverse conditions caused by heat, cold and
chemical agents are __________ .

a. psychrotrophic bacteria
b. facultative bacteria
c. sporeforming bacteria

8. Acidified low-acid foods are products with a pH less than or equal to ____.

a. 4.6
b. 4.2
c. 3.8

9. When low water activity is used to preserve a food, the most important
factor controlling microbial growth is

a. the amount of available water in the product.

b. the total water content.
c. a scheduled process approved by a processing authority with
supporting data.

10. Thermophiles are bacteria that grow best

a. at temperatures of about 80˚F to 98˚F (27˚C to 37˚C).

b. at temperatures of about 122˚F to 150˚F (50˚C to 66˚C).
c. in acid media.

26
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

The Microbiology of Low-Acid Canned Foods

►Clostridium botulinum

The pathogen of primary concern for low-acid foods in hermetically sealed

containers is not among those typically associated with illness from other meat
and poultry products, such as Salmonella – it is the sporeforming bacterium
Clostridium botulinum. The term “clostridium” indicates an organism that is able
to grow in the absence of air or oxygen and is a sporeformer. The term
“botulinum” comes from the Latin word “botulus,” meaning sausage, because the
organism was first isolated from a sausage that had produced the illness now
called “botulism.”

Clostridium botulinum (C. botulinum) is of great concern to home and commercial

canners because (1) when it grows it can produce a potent toxin, (2) it can be
isolated from soil or water practically everywhere in the world, (3) it is the
pathogen with the greatest heat resistance due to its ability to produce heat
resistant spores, and (4) canning foods provides an anaerobic environment
favorable to growth of the organism if it has not been destroyed by the process.
As noted before, the ability to form spores enables C. botulinum to survive a wide
range of unfavorable conditions, such as heat and chemicals. The spores
survive many heat processes that kill other pathogens of concern in meat and
poultry. In fact, certain types of C. botulinum spores are able to survive five to 10
hours in boiling water. (As you will learn later, processes to kill C. botulinum are
on the order of 250°F for 3 minutes, compared to, for example, 157°F for 15
seconds to kill Salmonella in certain cooked meat and poultry products.) Oxygen
is excluded from sealed containers, thus providing the anaerobic environment for
spores to germinate, become vegetative cells, multiply and produce toxin when
the foods are stored at temperatures that allow growth. It is important to
recognize that it is not the spore that produces the toxin, but the vegetative cell.
If spores are present but prevented from forming vegetative cells, as in acidified
foods, toxin will not be produced.

Certain strains of C. botulinum are called putrefactive because this term

describes the odor produced during their growth. These strains require proteins
to grow (they are proteolytic) and they grow best at temperatures between 86ºF
(30ºC) and 98ºF (37ºC), although growth can occur at any temperature between
50ºF (10ºC) and 104ºF (40ºC). Other strains, which are non-proteolytic, are
more dependent on carbohydrates, such as sugars and starch, for growth and do
not produce putrefactive odors. Some of these strains are associated with
marine environments; they grow best at 64-77°F (18-25°C) and have a minimum
growth temperature of 38ºF (3.3ºC). Their spores will not withstand heating to
212ºF (100ºC).

27
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Because C. botulinum spores are found everywhere, any raw food may be
contaminated with them (although, as was noted before, the organism is rare in
meats, and at low levels – 0.1 to 7 spores/kg – when present in meats).
However, it is only when the vegetative form of the organism grows in a food that
the toxin or poison is produced. Although the spores are heat resistant, the toxin
is not. The toxin can be inactivated by boiling temperatures – 212ºF (100ºC).

Heat processes for low-acid canned meat and poultry are designed, at a
minimum, to produce a product that is safe with respect to C. botulinum.
Microbial inhibitors and pH can impact the processes needed to inactivate
C. botulinum. Inclusion of sodium nitrite and sodium chloride in meat and poultry
products (e.g., commercially-sterile, canned cured meats) can lower the thermal
process required to produce a commercially sterile product that is stable at room
temperature. For example, processes equivalent to 0.4-0.6 minutes at 250°F
(121°C) are common for commercially sterile, cured luncheon meats containing ~
150 ppm ingoing nitrite and 5.0-5.5% brine strength. These processes may
range from 0.1 to 1.5 minutes depending on nitrite, brine strength and other
factors (compared to processes of 3.0 minutes for uncured products). (It should
be noted that there are both perishable and commercially sterile cured meat and
poultry products packed in hermetically sealed containers. If the products are not
commercially sterile, they are not subject to the canning regulations.) Reducing
the pH can also lower the process required, even when the product is not
acidified to a pH that produces an acidified food (see below).

►Other Microorganisms Important in Low-Acid Canned Foods

Although heat processes for thermally processed commercially sterile foods are
designed to destroy any microorganisms of public health significance, we are
also concerned about other microorganisms that could grow in the product under
normal storage conditions and result in adulterated product. As will be discussed
when we get to the principles of thermal processing, processes designed to
ensure commercial sterility of low-acid canned foods usually target Clostridium
sporogenes or similar organisms (putrefactive anaerobes). Because spores of
C. sporogenes have higher heat resistance than those of C. botulinum,
processes targeted to destroy spores of C. sporogenes will also destroy
C. botulinum spores.

Note that commercial sterility is not the same as absolute sterility – there may be
viable microorganisms present in commercially sterile products. Spores of
thermophilic bacteria such as Bacillus stearothermophilus or Clostridium
thermosaccharolyticum, if present, can survive processes that achieve
commercial sterility. However, these organisms, which are not harmful to
humans, cannot grow under normal conditions of storage. If product is properly
cooled and stored, generally the spores are not exposed to the high

28
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

temperatures they require for germination and growth. Although canned foods
are not generally processed to inactivate thermophiles, one exception to this is
hot-vended products. Products that will be held hot in vending machines will be
exposed to temperatures at which thermophiles can grow and will receive higher
processes to ensure thermophilic spoilage does not occur.

The Microbiology of Acidified Canned Foods

Meat and poultry products to which acids or acid products have been added to
reduce the pH to 4.6 or below are called acidified foods. Spores of C. botulinum
do not germinate and grow out in foods that have a pH below 4.8; a pH of 4.6 is
set for acidified foods to provide a margin of safety. Heat processes for acidified
foods target organisms other than C. botulinum, since the pH prevents its growth.
The safety of acidified meat and poultry products is achieved by controlling the
pH to 4.6 or less and applying a mild heat treatment to inactivate the vegetative
cells of pathogens (e.g., Salmonella, E. coli O157:H7 and C. botulinum).
However, achieving commercial sterility of these products requires treatments
that inactivate yeast, mold and bacteria, including some sporeformers, that could
grow in the product. The type of organism to be destroyed by the process will
depend on the pH of the product. If the pH is below 4.2, only vegetative cells
need be considered; however, if the pH is 4.2-4.6, processes may need to take
into account sporeforming organisms such as Bacillus coagulans and the butyric
acid anaerobes (e.g., Clostridium pasteurianum and Clostridium butyricum). For
more information on these organisms see the later section on Spoilage by Acid-
Tolerant Sporeformers.

The Microbiology of Shelf-Stable, Canned, Cured Meats

The safety and stability of shelf-stable, canned, cured meat products (e.g.,
canned hams and luncheon meats) are related primarily to the concentrations of
salt (sodium chloride, NaCl) and nitrite and the thermal process acting
synergistically. These products only receive mild heat treatments, relying on
NaCl and nitrite to inhibit surviving sporeformers, in particular C. botulinum. The
inherent low levels of spores in these products also contribute to ensuring safety
and shelf stability.

Canned Food Spoilage

►Indications of Microbial Spoilage

Most bacteria produce gas when allowed to grow in a canned food. This gas
causes the containers to swell. Exceptions are the flat-sour sporeforming

29
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

organisms, which produce acid and sour the food without producing gas, leaving
the container ends flat. These organisms are an economic but not a public
health problem.

The most obvious indicator of spoilage in processed food is a swollen container –

bulging at one or both ends. This implies that the food has possibly undergone
spoilage by the action of gas-forming bacteria. Consumers are advised by public
health officials, food trade associations and regulatory agencies not to use any
container with a bulged end or ends, even though the swelling may be of
non-microbial origin.

The appearance and odor of the container contents may also indicate spoilage.
If the product is broken down and mushy, or if a normally clear brine or syrup is
cloudy, spoilage may be suspected. In jars, a white deposit may sometimes be
seen on the bottom or on pieces of food. This is not always a sign of spoilage,
as starch sometimes precipitates from certain foods.

Bacterial decomposition of thermally processed product may result from one of

six causes:

1. Incipient spoilage – growth of bacteria before processing;

2. Contamination after processing – leakage of bacteria into the container;
3. Inadequate heat processing;
4. Growth of thermophilic bacteria in the processed food;
5. Spoilage by acid-tolerant sporeforming bacteria; and
6. Spoilage due to improper curing.

The last two causes of spoilage are specific to products with reduced pH and to
cured products, respectively. In addition, there can be non-microbial causes of
spoilage.

►Incipient Spoilage (Spoilage Before Processing)

Processed food is sometimes held too long between filling or closing the
containers and thermal processing. Such delays may result in growth of bacteria
normally present in the food and the initiation of spoilage before the retorting
process. This type of spoilage is referred to as “incipient spoilage.” The
microorganisms that grow will be killed by the process; with sufficient time,
sporeformers may germinate and form vegetative cells that will be killed.
Typically incipient spoilage manifests itself as low or no vacuum in the container
and a slight change in pH of the product. Generally no viable microorganisms
are recovered in subculture media. Although the product presents no risk to
public health, if there is sufficient growth, the product may be considered to be
adulterated (e.g., if the product characteristics are changed). The degree of

30
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

spoilage depends on the specific product and the time and temperature
conditions during the delay. For example, if the product has been heat treated
(e.g., cooked) prior to container filling, there may be low levels of bacteria
present such that holding product for several hours may result in bacterial
increases that are not significant. Products that contain inhibitors, those that are
held at lower temperatures (e.g., below 70°F) or those that are filled hot (above
microbial growth temperatures) may also demonstrate only limited bacterial
growth for several hours.

The loss of vacuum that can result from growth of microorganisms in sealed
containers held too long prior to retorting may lead to extensive internal
pressures in the containers during retorting. The build-up of internal pressure
strains the container seams or seals and increases the potential of leaker
spoilage. Some containers may actually buckle or rupture, rendering them
unusable. Steps should be taken to avoid such a delay before retorting the
containers.

►Contamination After Processing (Leakage)

Leaker spoilage – or post-processing contamination with microorganisms –

usually shows up rapidly as swollen containers. It may take several weeks until
all spoilage has ceased. If many swells are present, a small percentage of flat,
spoiled containers (flat-sours) may be expected, and normal appearing cans
should be examined with this potential in mind. Leakage is generally due to
inadequately formed seams, container damage or cooling water contaminated
with large numbers of microorganisms.

While theoretically leakage could result in post-processing contamination with

pathogens, this is unlikely in plants operating under good manufacturing
practices. Incidents of typhoid fever resulted from consumption of meat products
(imported into the UK from Argentina in the 1950s and 1960s) that were
contaminated when cans were cooled using river water contaminated with
sewage. Recontamination with C. botulinum has occurred with seafood, but not
meat products. Based on existing reports of food borne disease for which
package defects are alleged or proven to have contributed to the problem, the
probability of post-process contamination with organisms of public health
significance is extremely low. In fact, it was estimated in 1984 that the probability
of botulism from container leakage is about one chance in every 260 billion cans
of food consumed (or one potential botulism incident about every 9 years). The
report concluded that this probability compares well to the risk associated with
the minimum acceptable thermal process for low-acid canned foods.

31
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

►Inadequate Heat Processing

The term “inadequate heat processing” (also referred to as under-processing) is

almost self-explanatory. Heat processes for thermally processed food are
designed to destroy any microorganisms of public health, as well as non-health,
significance that could grow in the product under normal storage conditions. In
many instances, the product receives sufficient heat to inactivate pathogenic
sporeformers such as C. botulinum, with the more heat resistant spoilage
organisms surviving and spoiling the product. However, if the heat process is
inadequate to destroy C. botulinum, the situation can be very hazardous, since
botulinum toxin could be produced and, if the product is consumed, cause
botulism in the consumer.

Botulism is the disease caused by ingestion of the toxin produced when

C. botulinum grows in a food. Symptoms include, dry mouth, dizziness, and
weakness, generally within 12-48 hours after consumption of the toxin. Nausea
and vomiting may also occur. Neurologic symptoms follow, including blurred or
double vision, inability to swallow, difficulty in speech, descending weakness of
skeletal muscles and, ultimately, respiratory paralysis. Untreated, this can lead
to death.

A heat process may be inadequate for a variety of reasons, including but not
limited to the following:

1. If the time and/or temperature (or its equivalent) specified in the

scheduled heat process for the particular product in the particular size of
container is not used.
2. If the scheduled heat process was not established properly.
3. If the scheduled heat process is not properly applied because of some
mechanical or personnel failure.
4. If one or more of the scheduled process critical factors is not met.
5. If the formulation is changed such that the critical factors change.

►Thermophilic Spoilage

Generally, the higher the temperature at which a sporeforming organism can

grow, the greater the heat resistance of its spores will be. Thus, the spores of
thermophilic bacteria usually have a greater heat resistance than the spores of
mesophilic bacteria. The spores of thermophilic bacteria are so resistant to heat
that heat processes designed to kill the mesophilic bacteria may not be adequate
to destroy thermophilic bacteria. In order to prevent thermophilic spoilage, the
product must be properly cooled, preferably below 105ºF (41ºC), after thermal
processing and held below 95ºF (35ºC). Thermophiles may grow in equipment

32
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

that contacts food if the temperature is within their growth range. Consequently,
product should always be held at 170ºF (77ºC) or above or at room temperature
or below to prevent the growth of thermophiles.

For meat and poultry products containing ingredients known to be a source of

thermophiles (e.g., such as sugar, starch and/or spices) where thermophilic
spoilage may be a problem, prudent processors will use ingredients that the
supplier guarantees are free of thermophilic bacteria or that meet specifications
for thermophiles for canning processes. This is particularly important if the
product is to be hot-vended. This is the responsibility of the establishment, as it
is a quality issue, not one of safety.

►Spoilage by Acid-Tolerant Sporeformers

As noted above, acidified foods (those products with a pH 4.6 or below) do not
require a severe thermal process to assure product safety. Therefore a variety of
acid-tolerant sporeformers may survive the process. A thermal process
scheduled for acidified foods is designed to inactivate a certain level of these
sporeformers. Their survival is typically a result of excessive pre-processing
contamination. Sometimes underprocessing, either due to inadequate
processing or process deviations, may also result in survival of these acid-
tolerant sporeformers. The organisms of spoilage significance are butyric-acid
producing anaerobes and aciduric flat sour sporeformers.

The butyric-acid producing anaerobes, such as Clostridium butyricum and

Clostridium pasteurianum, are mesophilic sporeformers that produce butyric acid
as well as carbon dioxide and hydrogen. The spores are capable of germination
and growth at pH values as low as 4.2-4.4 and consequently are of spoilage
significance in acidified foods, particularly if the pH is above 4.2. In products
where the pH is not low enough, spoilage by butyric acid anaerobes may be
controlled by either further acidification of the product or by increasing the
thermal process. Growth of these organisms in foods is characterized by a
butyric odor and the production of large quantities of gas. Occasionally strains
will be encountered that can grow at a pH lower than 4.2. If these strains are
present in high numbers, the heat process may be inadequate and spoilage may
occur.

Aciduric “flat sours” are facultative anaerobic sporeformers that seldom produce
gas in spoiled products. The ends of spoiled cans remain flat; hence the term
“flat sour.” Spoiled products have an off flavor that has been described as
“medicinal” or “phenolic.” These organisms have caused spoilage in acid foods
such as tomato products (by Bacillus coagulans) and could cause problems in
meat products with tomato sauces if the sauces are prepared from fresh
tomatoes. (The problem is unlikely if the tomato ingredients are previously

33
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

processed to inactivate these organisms, as with commercially sterile products).

It may be necessary to ensure that the thermal process is adequate to inactivate
an expected number of spores, which can be determined through bacteriological
surveys. Pinpointing the ingredient that is contributing the most to the total spore
load may prove beneficial in process control. For example, proper handling of
vegetables prior to use, such as washing and culling, may help to reduce spore
loads.

Most food processing operations do not provide anaerobic conditions; therefore,

heavy build-up of acid-tolerant anaerobic sporeformers seldom occurs. This is
one reason why “dead ends” (“dead legs”) must be avoided in processing lines.
However, when this does occur, under-sterilization spoilage can result because
of the heavy load of spores in the product. The spoilage pattern within the
affected lots is often spotty and scattered, more typical of post-processing
spoilage that is due to container leakage, than of the pattern expected from
sporeformers that survive a thermal process. Thermal processing records and
other processing parameters usually give no indication of any irregularities. In
most cases, the problem can be identified only by investigation at the factory,
which includes a bacteriological survey, plus the absence of demonstrable
leakage and package defects in the spoiled containers.

►Spoilage Due to Improper Curing

As was noted before, canned cured meat and poultry products are made
commercially sterile by the interrelationship of salt, nitrite, heat and low levels of
spores. Spoilage due to underprocessing in canned cured meats is rare, and is
usually the result of improper curing rather than inadequate heating. The heat
processes for canned cured meat and poultry products are not designed to
inactivate mesophilic sporeformers, as their outgrowth will be inhibited by salt
and nitrite. Reduced levels of salt or nitrite can result in spoilage, as the heat
treatment may be inadequate for product containing these lower levels.

►Non-microbial Spoilage

Spoilage in canned foods can sometimes occur as the result of container

deterioration; this may at times result from chemical interactions of the food and
the container. To avoid this type of spoilage, the packer must be aware of the
impact of container, processing, and product chemistry variables on the corrosion
shelf life of the container. Container deterioration may result in swollen
containers resulting from the production of hydrogen (“hydrogen swells”) or in
leaking containers due to pinholes or cracks.

34
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Non-microbial spoilage rarely results in a health hazard. However, in high acid

products where detinning of containers has occurred, there have been instances
of illness due to high levels of tin (>200 ppm), which can cause acute toxicity
(nausea, vomiting, cramps and diarrhea). This has not been a problem in meat
and poultry products.

There are four main types of corrosion inside plain tinplate containers: normal
corrosion, rapid detinning, pitting corrosion and cosmetic corrosion. The normal
corrosion process is slow, even detinning of the tinplate surface. The canned
product will have a minimum shelf life of about 2 years. Rapid detinning involves
rapid tin dissolution of the tinned surface and pitting corrosion involves rapid
dissolution of iron, with or without tin dissolving. These two forms of corrosion
lead to either hydrogen swells or perforations. Cosmetic corrosion problems,
such as sulfide staining, are not of public health significance, but consumers may
reject the pack for aesthetic reasons.

Meat and poultry products are usually packed in enameled cans rather than plain
tinplate. Corrosion inside enameled cans is localized at fractures in the coating
where the plate is exposed to the product. There are five main manifestations of
corrosion in coated cans – 1) normal corrosion, 2) pitting corrosion, 3) under-
enamel corrosion and enamel flaking, 4)stress corrosion cracking and 5) sulfide
black corrosion. The normal corrosion process involves iron dissolution from
small pores, and the corrosion shelf life will exceed 18-24 months. Pitting
corrosion involves rapid iron dissolution from the container walls at coating
defects. Under-enamel corrosion is detinning or staining through the coating at
areas where the coating has lost adhesion. Stress corrosion cracking involves a
reaction between the container and stress inducing components in the product.
Cracks through the container have been observed in as little as 4 months.
Sulfide black corrosion involved rapid iron dissolution through the coating with
black deposits forming about 24 hours after processing. Sulfide black
discoloration is a type of cosmetic corrosion that is objectionable to the
consumer.

External corrosion involves rusting, detinning or staining of the outside walls of

the container. It rarely leads to perforations from the outside in. Filiform
corrosion involves tunneling through the walls of the can. It occurs at the scratch
defects in the coating on the outside of cans. It sometimes leads to pinholes in
the container.

►Determining the Cause of Spoilage

Analysis of spoilage of commercially sterile canned food products requires

expertise to conduct the analysis and to appropriately interpret the results. The
isolation of microorganisms from spoiled product does not necessarily mean they

35
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

are the cause of spoilage. For example, if acidified foods are cultured in neutral
laboratory media, microorganisms that are present in the product but are
inhibited by the pH may grow out. These are of no significance since they cannot
grow in the product due to its pH. Likewise, if other inhibitors are present in
product, culturing in laboratory media may dilute the inhibitors such that
microorganisms which are viable in the product but prevented from growing can
grow in the media. Again, it is unlikely that these organisms are significant with
respect to spoilage of the product. Thus, microbiological examination of products
intended to be commercially sterile requires a trained analyst following accepted
procedures such as those outlined in the USDA/FSIS Microbiology Laboratory
Guidebook for examination of heat processed, hermetically sealed (canned)
meat and poultry products or the equivalent.

36
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Workshop: Microbiology of Canned Products

The following questions are multiple-choice questions. Circle the answer(s) you
believe to be correct; some questions have more than one answer.

1. Commercial sterility refers to applying a heat treatment to a low-acid

canned food designed to destroy pathogens and spoilage organisms
capable of growing in the product at normal storage conditions. What is
the pathogen of greatest concern in a low-acid canned food?

a. Clostridium botulinum
b. E. coli O157:H7
c. Clostridium perfringens
d. Listeria monocytogenes

2. Certain types of Clostridium botulinum spores

a. produce a potent toxin.

b. are able to survive for 5 to 10 hours in boiling water.
c. produce toxin that cannot be inactivated by boiling at 212˚F
(100˚C).

3. Clostridium botulinum is

a. an anaerobic, sporeforming bacterium.

b. a mesophilic acid-tolerant microorganism.
c. a thermophilic microbe.

4. Botulism is an illness that can be caused by

a. eating spores of Clostridium botulinum or other food spoilage

organisms.
b. eating vegetative cells of Clostridium botulinum which may be
found in raw meat and spices.
c. eating food in which vegetative cells of Clostridium botulinum have
grown and produced toxin.

37
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

5. Incipient spoilage in canned foods is caused by

a. holding closed containers too long before retorting.

b. under processing.
c. post-process contamination, especially from dirty cooling water.

6. Thermophilic bacterial spores

a. are less heat resistant than mesophilic bacterial spores.

b. are never present in low-acid canned foods.
c. may not be destroyed during the heat process for low-acid foods.

38
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

Workshop: Spoilage of Canned Foods Case Study

(Note: This is a simplified training example only.)

While walking through the warehouse of Uncle Sam’s Canned Goods Company,
you and the warehouse supervisor notice several cases of canned beef stew that
look wet. The QA manager is called to the warehouse to inspect the problem.
Upon opening the cases he finds several cans that are swollen or leaking. He
pulls out the swollen and leaking cans, along with several of the normal-looking
flat cans. He then sends some of the sample cans to Microtesting, Inc., a
microbiology laboratory that specializes in analyses of canned food products.
You send the remaining samples to the FSIS laboratory in Athens, Georgia. The
lot of product is placed on hold pending the laboratory results.

Upon receipt of the samples on Friday afternoon at 4:45pm, the diligent

laboratory technician at Microtesting, Inc., begins analysis of the samples. The
laboratory sends back preliminary results to the QA manager the following week.

The laboratory results listed below are four possible “what-if” scenarios. Please
read the possible scenarios then answer the following questions.

Microbiological Results Container Evaluation

Scenario #1 Thermophilic microorganisms were No container defects
identified. were detected.
Scenario #2 Mixed culture of rods and cocci Can exam revealed false
were identified. seam on packer’s end.
No sporeformers or heat resistant
microorganisms were recovered.
Scenario #3 Mesophilic organisms with spores No container defects
were identified. were detected.
Scenario #4 No viable bacteria (sporeformers or Hydrogen gas was
non-sporeformers) were recovered. detected.

►Questions

1. Which of these scenarios, if any, suggests microbiological problems due

to potential under-processing? Why?

39
FSRE Shelf-Stable
 Microbiology of Commercially Sterile and Shelf-Stable Products
6/30/05

2. Which of these scenarios, if any, suggest post-process contamination?

Why?

3. Which of the scenarios, if any, is indicative of microbial spoilage that has

the potential for an adverse public health consequence?
Why?

4. Which of the scenarios, if any, is indicative of detinning of the can interior?

Why?

5. After receiving the results indicated in Scenario #1, Uncle Sam’s decides
to sort and remove the swollen and leaking cans from the lot and release
the normal cans.

The lot of cans are incubated in an unair-conditioned trailer held at 110-

120˚F and checked weekly. After 6 weeks there are no additional swollen
containers. Since the cause of spoilage was the growth of thermophilic
microorganisms, the plant manager believes that it is acceptable to
release the flat containers. The plant microbiologist wants to conduct a
simple test to determine the pH of random samples before making the
decision to release. Why?

6. Is every swollen can an indication of an adverse public health

consequence? Why or why not?

40
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

PRINCIPLES OF THERMAL PROCESSING

The “canning” of foods has been practiced for almost 200 years, but the science
supporting the canning process has been understood for only about half of that
time. In this section we will discuss the theory and science that forms the basis
for the development and application of thermal processes to low-acid and
acidified foods packaged in hermetically sealed containers. This section will
identify and review some of the major factors affecting thermal processing of
canned food products.

The objectives of this section are for you to be able to:

1. define commercial sterility;

2. identify who can establish a thermal process;
3. identify the components in establishing a thermal process;
4. identify factors that impact the thermal process; and
5. recognize a process deviation.

The Scheduled Process

As mentioned in the Introduction Section, “canned” products are treated with heat
to make them commercially sterile. The condition of commercial sterility (or
shelf-stability as it is characterized in the FSIS Canning Regulations -9 CFR
318.300 and 9 CFR 381.300) is recognized as follows:

Commercial Sterility – The condition achieved by application of heat,

sufficient alone or in combination with other ingredients and/or
treatments, to render the product free of microorganism capable of
growing in the product at nonrefrigerated condition (over 50°F or
10°C) at which the product is intended to be held during distribution
and storage.

A condition of commercial sterility will result in products that are safe to eat
because the pathogens of concern are destroyed or inactivated. The product will
remain shelf-stable as long as the container is intact because any spoilage
organism that favors the environmental conditions within the container (i.e.,
anaerobic) and normal storage temperatures (i.e., mesophilic bacteria) are also

41
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

destroyed with the thermal process. The current FSIS Canning Regulations
(9 CFR 318.300 and 9 CFR 381.300) refer to this condition as shelf-stability, but
in this course we will refer to “canned” products as being commercially sterile to
avoid confusion with the dry and semi-dry meat and poultry products that are
also shelf-stable.

The application of heat to make a product commercially sterile is conducted in a

controlled manner; this has been traditionally called the scheduled process or
process schedule. The FSIS Canning Regulations (9 CFR 318.300 and 9 CFR
381.300) require that scheduled processes be established by a processing
authority. A processing authority is a person or organization having expert
knowledge of thermal processing requirements for foods packed in hermetically
sealed containers and having adequate facilities to make these process
determinations.

The scheduled process, as designed by a processing authority, if properly

executed, will produce a commercially sterile product. The scheduled process,
includes thermal processing parameters such as initial temperature of the
product, the process temperature and the process time, plus any other critical
factors that may affect the attainment of commercial sterility. Critical factors may
include any characteristic, condition or aspect of a product, including formulation,
container, preparation procedures, or processing system that affect the
scheduled process. We will discuss critical factors again later in this section.

Processing authorities use their knowledge of food microbiology (specifically,

thermobacteriology), heating characteristics of food, and processing systems as
the basis for process schedule establishment. Contrary to other cooked meat
and poultry products, the cook process for commercially sterile products is
controlled by monitoring the process parameters (such as process temperature
and time) rather than monitoring a temperature of the product. Temperature and
time are easily controlled and monitored to ensure delivery of a proper thermal
process.

For low-acid canned foods (those with a pH greater than 4.6), the thermal
process focuses on the destruction of the spores of certain sporeforming
bacteria. (These have been discussed in the previous section). The target
pathogen for low-acid canned foods is Clostridium botulinum (specifically the
spores of the organism.) Failure to destroy these spores, followed by
germination and growth, can lead to the production of the deadly botulinum toxin,
an extremely potent neurotoxin. Low-acid canned food processes that assure

42
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

the destruction of C. botulinum spores are adequate to protect human health;

however, as noted previously, a more substantial process, or a commercial
sterility process, is required to destroy spores of other microorganisms that could
germinate and grow under normal storage and handling conditions and cause
economic spoilage. The target for commercial sterility is typically C. sporogenes,
an organism very similar to C. botulinum but with a higher heat resistance.

Thermal processes for acidified foods are targeted toward vegetative cells of
microorganisms and are generally significantly milder than those applied to low-
acid foods. This is primarily because spores of microorganisms such as
C. botulinum will not germinate due to the acid nature in the product. Keeping
the spores from germinating will prevent the growth of the vegetative cells of
C. botulinum and subsequent toxin production. In distinguishing between
acidified and low-acid foods, the standard used is a pH of 4.6 (greater than 4.6 is
low-acid and less than or equal to 4.6 is acid or acidified). Typical thermal
processes for acidified foods will maintain the commercial sterility of a product as
long as good sanitation and GMPs are followed. Lack of pH control for an
acidified food can lead to problems if the pH is high enough to allow surviving
spores of C. botulinum to germinate and produce toxin.

Determining the scheduled process with the proper temperature and process
time needed to produce commercially sterile products has been the subject of
years and years of study in the canning industry. Sound process determinations
depend upon good knowledge of the :

1. nature of the product and how it heats;

2. container in which the product is packed;
3. details of the thermal processing procedures used; and
4. characteristics of the target microorganisms such as growth, survival, and
thermal resistance.

These four factors are related to the thermal resistance of the microorganisms
and the heating characteristics of the product. Utilizing all this information, the
processing authority will establish a thermal process that will specify the amount
of time at a specific temperature necessary to ensure the destruction of
C. botulinum and spoilage organisms that may be present.

43
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

Establishing a Thermal Process

As mentioned previously, the processing authority will base the establishment of

a thermal process for a particular food product on two separate factors: 1) the
thermal (also known as heat) resistance of the microorganism of choice in that
food and 2) the heating characteristics of the product. In simplified terms, the
processing authority needs to know 1) how much heat and for how long is
necessary to destroy microorganisms in the food product and 2) how fast does
the product heat (in the case of conventional canning) or how does the product
flow (in the case of aseptic processing). The combination of these two factors is
used to establish the thermal process.

The establishment of the thermal process will also depend upon the method of
processing: conventional canning or aseptic processing. As noted in the
Introduction section, in conventional canning, the product is filled into the
container, the container is hermetically sealed, and the container and product are
thermally processed at a specified time and temperature to achieve commercial
sterility. For aseptic processing, packages or packaging material and the food
product are sterilized in separate systems. Product sterilization involves heating
a pumpable product to a sterilizing temperature and holding it at that temperature
for sufficient time to sterilize the product. The packaging materials are sterilized
with heat, chemicals, radiation or a combination. The sterile package is then
filled with sterile product, closed and hermetically sealed in a sterile chamber.

Once a process has been established for a particular food, it is specific for that
particular set of parameters regarding formulation, preparation, thermal
processing system, container, etc. Since a seemingly insignificant change in any
of these parameters could result in under-processing, it is important that
processes not be altered without consultation with a processing authority.

Thermal Resistance of Microorganisms

The thermal resistance of microorganisms (vegetative cells or spores) is

dependent upon a number of factors: 1) the growth characteristics of the
microorganisms, 2) the nature of the food in which the microorganisms are
heated, and 3) the kind of food in which the heated microorganisms are allowed
to grow. Because of the variability of any biological entity, thermobacteriology is
a highly complex science, and variations in any of these factors can affect the
heat resistance of microorganisms.

44
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

►Thermal Death Time (TDT) Tests

The amount of heat required to destroy microorganisms in a product can be

determined through thermal death time (TDT) tests. TDT tests are conducted by
thermobacteriologists in a laboratory. Very few food processing establishments
have the facilities to conduct TDT tests on-site. The instrumentation and
equipment used for TDT tests include TDT retorts, tubes, and/or cans;
three-neck flask, oil baths, sealed plastic pouches, and/or capillary tubes. The
equipment and instrumentation used will depend on the type of product being
tested – whether it is low-acid, acidified, thick puree, solid or a liquid.

TDT tests involve heating a known amount of microorganisms in a buffer solution

or food at several temperatures and for several time intervals at each
temperature. The results from the TDT tests are used to calculate D- and z-
values. These values are used to define the heat resistance of the
microorganisms of concern.

►Determination of D- and z-values

In conducting TDT tests, the thermal characteristics (D- and z-values) of the
microorganisms will be determined. The D-value is defined as the time at a
particular temperature required to reduce a known number of microorganisms by
90% or to result in a 1-log reduction. This is also termed the decimal reduction
time because exposure for this length of time decreases the population by 90%,
thus shifting the decimal point in the number of microorganisms remaining one
place to the left. For example, if you had 100,000 spores and if exposing them to
a temperature of 240°F for 3 minutes reduced the count to 10,000 spores, the
D240°F would be 3 minutes.
The D-value decreases as the temperature increases, since it takes less time to
destroy the microorganisms at the higher temperature. By determining the D-
values at various temperatures, a z-value can be determined from the slope of
the line that results from plotting the log of D-values versus temperature. The z-
value, indicative of the change in the death rate based on temperature, is the
number of degrees between a 10-fold change (1 log cycle) in an organism’s
resistance. As an example, suppose that z = 18°F and the D232°F = 3 minutes.
The D250°F would be 0.3 minutes. (Because 232°F + 18°F = 250°F and 3 minutes
/ 10 = 0.3 minutes.) Both D- and z-values are indirectly used to establish thermal

45
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

processes.

►“Minimum Health” and Commercial Sterility Processes

Traditionally, a 12D process for spores of C. botulinum has been used to assure
public health protection for low-acid canned foods. This has been based on
historical data indicating that a heavy load of C. botulinum spores in a canned
food product would be 1012 spores; therefore, a 12D reduction would provide a
one-in-a-billion chance that a spore would survive in a canned food. For all
practical purposes the 12D process is very conservative, as it is highly unlikely
that spore loads of C. botulinum would approach these levels, especially in meat
and poultry products. (Remember, Clostridium botulinum is rare in meats, and
when present is there in very low numbers - 0.1 spore to 7 spores per kg meat.)
A typical D-value for C. botulinum spore destruction in many foods is ~0.2
minutes at 250°F; therefore, a 12D destruction would be ~2.4 (=12 x 0.2) minutes
at 250°F. (A value of 3 minutes is sometimes used to incorporate a margin of
safety.) However in some products, the components of a food (or ingredients in
a formulated food) can have adverse or beneficial effects on the thermal
destruction of spores and will impact the D-values. For example, if 3 minutes at
250°F is needed to ensure public health at pH of 6.0, 2.0 minutes may be
sufficient if the food is acidified to pH 5.3. (See discussion of Fo values on the
next page.) Processing authorities refer to the times and temperatures needed
to inactivate C. botulinum as “minimum health” processes because this is what is
necessary for public health protection.

In order to attain commercial sterility, a thermal process more strenuous than that
required for public health protection must be provided. Commercial sterility
means the condition achieved in a product by the application of heat to render
the product free of microorganisms capable of reproducing in the food at normal
non-refrigerated conditions of storage and distribution. A commercial sterility
process will destroy other spores in addition those of C. botulinum. These
spores, if not destroyed, have the potential to grow under normal storage and
handling conditions and cause economic spoilage, even though they pose no
public health risk. A 5D destruction of C. sporogenes spores (such as PA3679)
is the target for commercial sterility. This 5D process for C. sporogenes spores
is more lethal than a 12D process for C. botulinum spores due to the fact that
spores of C. sporogenes are more heat resistant than spores of C botulinum.

In order to compare thermal processes calculated for different temperatures, a

46
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

standard Fo value is assigned for each product. This Fo value is the time in
minutes (at a reference temperature of 250°F and with a z = 18°F) to provide the
appropriate spore destruction (minimum health protection or commercial sterility).
As previously noted, using D- and z-values, this reference value at 250°F can be
converted to other temperatures. Due to a variety of factors (e.g., influence of
the food on the destruction of spores) different foods will have different Fo values.
For example, if an Fo of 6 minutes is needed to ensure commercial sterility at pH
of 6.0, an Fo of 4 minutes may be sufficient if the food is acidified to pH 5.3. In
cured meat products containing 150 ppm nitrite and 3-4% brine (% NaCl X 100/
% NaCl + % water), an Fo of 0.3–1.5 minutes may be sufficient to render the
product commercially sterile.

Fo values are already established for many food products. However, there are
times, such as for novel formulas of food products, when TDT work may be
needed to determine D- and z-values and appropriate Fo values for spores of
C. botulinum and C. sporogenes for a specific product. In the absence of TDT
data on a specific formulation, a processing authority will apply a conservative Fo
that is known to result in a safe product.

Product Heating Data Determinations

Processing authorities determine product heating characteristics through the use

of heat penetration tests. The rate at which a product heats can be measured
using devices to monitor the rate of change in temperature of the food as it is
being heated within the container (heat penetration studies). These
determinations are made with a temperature sensor or thermocouple located in
the product at the slowest heating region of the container. The slowest heating
region will depend on the type of product, container size, processing method and
the heat transfer mechanism. Typical heat transfer mechanisms in canned foods
are convection (heat current flowing within the container as experienced in
canned broths), conduction (molecule to molecule as experienced in corned beef
hash), and combinations (for example, convection then conduction due to
thickening of the product as maybe experienced in formulated products such as
chicken and dumplings). The number of containers per run and the number of
runs necessary to ensure the data are adequate depends on the variability of the
product and the processing system. When either demonstrates significant
variability, additional containers/runs may be required to ensure confidence in the
process.

47
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

The need to simulate the worst case scenario likely to occur when producing
product cannot be overstated, because the thermal process is controlled by
monitoring and controlling the process parameters rather than with the actual
temperature of the product. The processing authority will review variables in
product preparation such as changing a starch or protein in the formulation, filling
procedures, rehydration procedures, etc., to determine the impact on the heating
rate of the product. More viscous product, higher fill weights, or improperly
rehydrated product can all affect the heating rate of the product. If the heat
penetration tests do not account for this effect or if the establishment can not
control for these variations, the result could be under-processed product.

The heating characteristics of the product aseptically processed are also

important. For aseptic processing, the heated product flows at a constant rate
through tubing of a specified length; it is the flow characteristics of the product
that determine whether certain particles in the fluid stream move through the
tubing faster than others. The speed of the fastest moving particles (which
remain at the elevated temperature for the shortest time) and the temperature of
the flowing product determine the heat (lethality) attained by the product.

Process Schedule Calculations

For conventionally canned products, the process authority will calculate a

process using the product heating data and the thermal resistance data for the
significant spoilage organisms or organisms of public health consequence
expected to be present in the product. These mathematical procedures combine
the Fo value that provides commercial sterility with the factors that define the
product heating rate. There are several acceptable methods for calculating
thermal processes. Some of the more common methods are the General
Method, the Ball Formula Method, and the NumeriCAL™ Method.

For aseptically processed products, the process authority will calculate a process
using the flow characteristics of the product and the thermal resistance data for
the significant spoilage organisms or organisms of public health consequence
expected to be present in the product. The resulting process schedule will
indicate a specific sterilization time or residence time at a specific temperature.
The residence time is directly related to the rate of flow of the fastest moving
particle/fluid stream through the system.

Although the method of characterizing the product heating rate is different for

48
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

conventionally canned and aseptically processed products, the Fo value for a

particular food is the same in either processing method.

ACIDIFIED FOODS

Products that are high acid (have a low pH) or are acidified to a pH of 4.6 or less
do not require a high temperature process. The foods may be processed at the
temperature of boiling water – 212°F (100°C) – or lower. The thermal process is
designed to destroy vegetative cells and some spores of low heat resistance.
The product’s low pH (4.6 or less) will prevent the remaining spores from growing
out.

To produce products with a pH of 4.6 or less, acidification must be properly

carried out. Here are some methods to obtain properly acidified foods.

1. Blanch the food ingredients in an acidified aqueous solution. To acidify

large food particulates, the particulates could be blanched in a hot acid bath. The
ability to obtain a properly acidified product is dependent upon blanch time and
temperature, as well as the type of and concentration of acid.

2. Immerse the blanched foods in an acid solution. That is, blanch the
product in the normal steam or water blancher. Then, dip it into an acid solution,
remove it from the acid solution and place it into containers. Proper acidification
depends upon how well the product is blanched, the concentration of the acid
and the contact time.

3. Direct batch acidification. This is normally the best way to acidify fluid
material. Ingredients are mixed in a kettle, and acid is added directly to the batch.
(An elevated temperature may improve the rate of acid penetration into solid
particles.) The pH of the batch is checked before the material is sent from the
batch kettle to the filler.
4. Add acid foods to low-acid foods in controlled portions. Essentially, this
is how a formulated product such as pasta sauce is made. Components in the
sauce, such as meat or onions, are low-acid foods, while the tomato sauce is an
acid food. The acid food is mixed with the low-acid food to get an acidified food
product. The formulation, including the proportion of tomato sauce to low-acid
components, is critical to obtain uniform and accurate control of pH of the
finished product.

5. Directly add a predetermined amount of acid to individual containers

49
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

during production. This involves addition of acid pellets, known volumes of acid
solution, or some other means for direct acidification of each container. This is
probably the most inaccurate and least consistent method of acidification,
because acid addition to a given container may be overlooked. Although this is a
permissible way to acidify, it is not recommended and it is not used for meat and
poultry products.

Processes for acidified foods may involve a hot-fill-hold process or the

conventional canning process. Hot-fill-hold processing involves filling the product
hot, sealing the container, then holding filled containers for a period of time at or
above a certain temperature before cooling. Acidified products may also be
processed in a pasteurizer, atmospheric cooker or retort for a given period of
time to destroy the target microorganisms. The processing authority will calculate
a process using pH, fill temperature, and the thermal resistance data for the
significant spoilage organisms.

INOCULATED TEST PACK

It is possible and sometimes desirable (e.g., with new products or new

processing systems) to confirm the calculated process by means of inoculated
test packs. In this procedure, the test product is prepared under commercial
plant operating conditions. Appropriate test microorganisms of known heat
resistance are added to the product. (It is undesirable to use C. botulinum
spores in processing plants processing low-acid canned foods due to the risk
associated with the potential toxin production.) The product is inoculated with a
known number of microorganisms and is then subjected to various processing
times at one or a number of different processing temperatures. The product is
then incubated at an appropriate temperature for growth of the test organism.
Product that received a process inadequate to destroy the added
microorganisms will show evidence of spoilage. A satisfactory process is
demonstrated by the absence of spoilage. Substantial agreement between
calculated processes and those determined by inoculated packs furnishes the
strongest possible assurance of the adequacy and safety of a particular process.

Occasionally, due to peculiarities of the thermal processing systems or the

product, reliable heating data cannot be obtained. Under these circumstances,
consideration may be given to using an inoculated pack alone to establish a safe
thermal process.

50
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

Process Deviations

A deviation in processing (or a process deviation) occurs whenever an actual

thermal process is less than the scheduled process (or process schedule) or
when any critical factor does not comply with the requirements for that factor as
specified in the process schedule. Common causes of process deviations for
traditional canning operations include failure to meet initial temperature, process
time, or retort temperature requirements or failure to meet any other specified
critical factor. For aseptic processing and packaging systems, deviations can
result from improper hold tube temperature, flow rate, or package sterilization;
breach of the aseptic zone; etc. According to FSIS regulations (9 CFR 318.308
and 381.308) deviations involving meat and poultry products may be handled in
accordance with a HACCP plan for canned product that addresses hazards
associated with microbial contamination or alternative documented procedures
that will ensure that only safe and stable product is shipped in commerce.
Otherwise, deviations must be handled in accord with procedures specified in
paragraph (d) of the regulations.

Product involved in deviations identified during processing may be immediately

reprocessed using the full scheduled process, may be given an appropriate
alternate process established in accordance with FSIS regulations, or may be
held for later evaluation by a processing authority to determine its safety and
stability. It should be kept in mind that, in some cases, the original process may
change the heating characteristics of the processed product (e.g., thickening due
to starch). For this reason it is a good idea to consult with the processing
authority to assure that the reprocess is adequate for the product and conditions
of use.

Upon completion of the evaluation of the process deviation, the establishment

maintains a complete description of the deviation along with all necessary
supporting documentation; a copy of the evaluation report; and a description of
any product disposition actions, either taken or proposed. Product handled in
accordance with paragraph (d) of the regulations shall not be shipped from the
establishment until the inspection personnel have reviewed all of the information
submitted and the product disposition actions.

If an alternate process schedule is used that is not on file with the inspector or if
an alternate process schedule is immediately calculated and used, the product
shall be set aside for further evaluation as noted above.

51
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

Product involved in process deviations that are identified through review of

processing and production records shall be held and the deviations evaluated by
a processing authority in accord with the requirements noted above. If product
involved in a deviation is destroyed, destruction shall be conducted in
accordance with FSIS regulations.

FSIS regulations also require the maintenance of a process deviation file. The
establishment shall maintain full records regarding the handling of each
deviation, regardless of the seriousness of the deviation. Such records shall
include, at a minimum, the appropriate processing and production records, a full
description of the corrective actions taken, the evaluation procedures and results,
and the disposition of the affected product. Such records shall be maintained in
a separate file or in a log that contains the appropriate information. The file or log
shall be retained for no less than one year at the establishment, and for an
additional 2 years at a suitable location. The file or log shall be made available to
inspection personnel upon request.

52
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

Workshop: Process Letter Review

Note: This is a simplified example prepared for instructional purposes only.

Review the following process letter and answer the questions.

1/24/2005

Dr. John Smith

Food Safety Manager
Uncle Sam’s Canned Goods Company
1234 E. Canning Plant Rd
Somewhere, ST 12345-1234

Dear John,

Based on the heat penetration data that you provided to us, we would
recommend the following thermal processes for your Chili No Beans in 300X407
metal cans.

Processing Conditions

Product: Chili No Beans

Processing System: Water Immersion with Container
Rotation
Container Size: 300x407 metal cans
Least Sterilizing Value (Fo) 5.3
Critical Factors:
Fill weight of fully soaked beans: 10.0 ounces
Container orientation: Vertical
RPM: 18-20
Headspace (inches): 10/16
Product: Preparation method and Formulation
Minimum come up time (minutes): 13

53
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

Process Time in Minutes

Process Time (minutes at Retort Temperature (°F))

Initial Temp. (°F) 250 251 252
90 40 39 38
100 39 38 37
110 38 37 36
120 38 37 36

These processes are designed to produce a commercially sterile product

provided that all processing and packaging operations are completed
satisfactorily. Please give us a call if you have any further questions.

Sincerely yours,

Kelly White
Senior Scientist, TPA, Inc.

Questions:

1. What are the critical parameters that will need to be controlled by Uncle
Sam’s Canned Goods Company when processing this product?

2. There are several errors on the process letter. Please identify the errors
or information that needs to be clarified.

54
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

3. What would be the impact if the headspace requirement was not met?

4. What would be the impact if the beans were not soaked?

5. What process time would Uncle Sam’s Canned Goods Company use if the
product initial temperature was 115°F and the retort was operated at
252°F?

Uncle Sam’s Canned Goods Company has set the following as the operating
process for this product:

Minimum IT = 100ºF
Minimum Retort Temperature = 252ºF
Minimum Process Time = 40 minutes

6. Would the operating process result in a higher or lower Fo than the

scheduled process? Why would the firm use an operating process rather
than a schedule process?

55
FSRE Shelf-Stable
 Principles of Thermal Processing
5/11/2005

7. Which of the following situations is a processing deviation?

IT = 90ºF IT = 100ºF IT = 112ºF

RT = 250ºF RT = 251ºF RT = 249ºF
Process Time = 40 Process Time = 42 Process Time = 42
minutes minutes minutes

56
FSRE Shelf-Stable
 nomenclature

Institute For Thermal Processing Specialists

NOMENCLATURE FOR STUDIES IN THERMAL PROCESSING

Various symbols have been employed to represent measured and derived variables in the applications of
thermal processing science. The overall objective of these guidelines is to recommend a standard system
of nomenclature for thermal processing applications. The following recommendations are to be
considered voluntary guidelines. While this does not preclude the use of other symbols, these
guidelines have been developed by consensus of the Institute for Thermal Processing Specialists and
should be given serious consideration for adoption by individuals involved in thermal processing studies

aw - Water activity defined as the ratio of the partial pressure of water above a food to
the water vapor pressure of pure water above a food (p) to the water vapor pressure of pure
water (po) at a given temperature (aw= p/po)

A - Frequency factor in the Arrhenius equation, K = A exp (-Ea/RT) where T is

expressed in Kelvin

c - Cook rate, c = 10(T - Tx)/z

C - Concentration of a nutrient or chemical component

- Cook value used to relate a high temperature thermal process to an

equivalent process at stove top temperatures, generally applied with T=100°C (212°F)
and a z-value related to quality attributes

DT - Decimal reduction time equal to the time at a given temperature, T, for a

survivor curve to traverse one log cycle or equivalently, to reduce a microbial
population by 90%, t = DT(log No - log N)

Ea - Activation energy in the Arrhenius equation, K = A exp(-Ea/RT), Ea=

1.8*2.303*R*Tx*T/z where Tx and T are expressed in Kelvin

f - Temperature response parameter equal to the time for the linear section of a

file:///C|/iftps/protocols/nomenclature.htm (1 of 6)6/5/2004 8:29:06 AM

nomenclature

heating or cooling curve plotted on semi-log coordinates to traverse one log cycle

f2 - Temperature response parameter of the second straight line segment of a broken

heating curve

fc - Temperature response parameter derived from the cooling curve

fh - Temperature response parameter derived from the heating curve

F - Time intercept from a thermal death time curve (log tgmvs T) at T = Tx

- Accumulated lethality to reflect the total lethal effect of heat applied;

expressed as equivalent minutes at a specific reference temperature for a specific z-

value, = DT(log No - log Nf) = DTYN; may also be referred to as F-biological

Fc - Accumulated lethality in the cooling phase

Fh - Accumulated lethality in the heating phase

Fi - Factor relating the lethality at the retort temperature to lethality at the reference
temperature, Fi = 10(Tx - Tr)/z

Fo - Accumulated lethality when Tx = 121.1°C (250°F) and z = 10 C° (18 F°)

Fs - Integrated lethal or degradative capacity of heat received by all points in a

container during a process

- Accumulated lethality at an iso-j surface

g - Unaccomplished temperature difference, g = Tr - Tc

gc - Unaccomplished temperature difference at the end of the heating period, gc = Tr -

Tic

gbh - Unaccomplished temperature difference at the intersection of fh and f2 for a broken

heating curve

file:///C|/iftps/protocols/nomenclature.htm (2 of 6)6/5/2004 8:29:06 AM

nomenclature

gih - Initial unaccomplished temperature difference, gih = Tr - Tih

- Unaccomplished temperature difference at an iso-j surface

Ir - Ratio of the log of the straight line survivor curve zero intercept to the initial spore
count (No)

jc - Cooling lag factor, jc = (Tw - Tpic)/(Tw - Tic)

jcl - Cooling lag factor associated with an iso-j surface

jh - Heating lag factor, jh = (Tr - Tpih)/(Tr - Tih)

k - Reaction rate constant for base 10 logarithms

K - Reaction rate constant for base e (natural) logarithms; death rate constant in the
Arrhenius model, K = 2.303/D

L - Lethal rate expressed as minutes at the reference temperature per minute at the
product temperature, L = 10(T - Tx)/z

m - Unaccomplished temperature difference during cooling, m = Tc - Tw

mic - Value of m at the beginning of the cooling cycle, mic = Tic - Tw

n - Number of samples

N - Number of surviving microorganisms

No - Initial number of viable spores or vegetative cells before heat is applied, initial
bioburden

Nf - Final number of surviving spores or vegetative cells after heat is applied

Nmp - Most probable number of survivors in a thermal resistance experiment

Ns - Number of microbial cells remaining after a preservation treatment to a

file:///C|/iftps/protocols/nomenclature.htm (3 of 6)6/5/2004 8:29:06 AM

nomenclature

specified probability of finding a non-sterile unit; end point process specification

pH - The degree of acidity or alkalinity of a water solution

- Pasteurizing value used in place of F-value for pasteurizing processes

P - Pasteurizing value defined as the accumulated lethality when Tx= 60°C (140°F) and
z = 10 C°(18 F°)

R - Number of negative responses in a thermal resistance experiment

R - Universal gas constant, 1.987 cal/mol×K, 8.314 J/mol×K where K refers to Kelvin
temperature units

t - Time

tB - Ball's process time, tB = tp + 0.42 tc simple heating, tB= fh(log jhgih-log gc) broken
heating, tB= fhlog jhgih+(f2 - fh)log gbh- f2log gc

tc - Come-up time is the time between the start of heating and the time when the retort
reaches processing temperature

tD - Time when the first sample exhibiting no growth is observed in a thermal death time
(TDT) experiment

tp - Process time is the time from the end of the come-up period to the end of heating,
defined as tp = tB - 0.42 tc in the Ball Formula Method

tS - Time when the last sample exhibiting growth is observed in a thermal death time
(TDT) experiment

tbh - Time measured from tB = 0 to the intersection of fh and f2 for a broken heating
curve

tgm - Geometric mean time, square root of (tS * tD)

T - Temperature

Tc - Container center or coldspot temperature

file:///C|/iftps/protocols/nomenclature.htm (4 of 6)6/5/2004 8:29:06 AM

nomenclature

Tic - Product temperature at the start of the cooling cycle

Tih - Initial product temperature measured before heating

Tpic - Pseudo-initial cooling temperature determined by extrapolating the linear portion of

a cooling curve to the start of cooling

Tpih - Pseudo-initial heating temperature determined by extrapolating the linear portion of

a heating curve to time, tB = 0

Tr - Retort temperature

Ts - Mass average temperature

Tw - Cooling water temperature

Tx - Reference temperature

U - Sterilizing value in terms of minutes at the heating medium temperature, U = FoFi =

Fo/L

Uc - Sterilizing value for the cooling phase

Uh - Sterilizing value for the heating phase

YN - Spore-log reduction, YN = log No - log Nf

Ys - Spore-log reduction to reach a specified probability of finding a non-sterile unit, Ys=

log No - log Ns

z - Number of degrees of temperature required for the thermal death time curve
(log F vs. T) or thermal resistance curve (log DT vs T) to traverse one log cycle, z = (Tx
- T)/(log FT - log FTx) or z = (Tx - T)/(log DT - log DTx)

a - Thermal diffusivity, a =thermal conductivity/(specific heat * density), is

inversely proportional to fh where the proportionality constant is related to the container
geometry

file:///C|/iftps/protocols/nomenclature.htm (5 of 6)6/5/2004 8:29:06 AM

nomenclature

r - Fraction of total lethality delivered during heating, r = Uh/(Uh + Uc) or r = Fh/( Fh

+Fc)

• The Institute for Thermal Processing Specialists is a non-profit organization established

exclusively for the purpose of fostering education and training for those persons interested in
procedures, techniques and regulatory requirements for thermal processing of all types of food or
other materials, and for the communication of information among its members and other
organizations.

• Part of the mandate of the IFTPS Committees is to develop protocols to be used as guides for
carrying out the work of thermal processing specialists. This is the first such protocol prepared by
the Committee on Temperature Distribution and reviewed extensively by members of the Institute.
The protocol has been approved by the Board of Directors. This document may be photocopied
in its entirety for use.

• Single copies of the protocol, as well as information on membership in IFTPS may be obtained
from: Institute for Thermal Processing Specialists, 304 Stone Rd. W. Ste. 301, Guelph, ON N1G
4W4 Phone: (519) 824 6774 Fax: (519) 824 6642, E-Mail: info@iftps.org

file:///C|/iftps/protocols/nomenclature.htm (6 of 6)6/5/2004 8:29:06 AM

 FOOD SCIENCE 4075
LAB_____
THERMAL PROCESS CALCULATION

WARNING: This lab contains at least 28 pages - you may not want to print the entire thing - just
what you need.

PURPOSE: Demonstrate the techniques involved in determining the processing time and
temperature for canned food products.

MATERIALS: Two food products; one heavy, semisolid and one more liquid, cans,
thermocouples, multipoint recorder, retort, sealer

PROCEDURE: In order to determine the processing time for a certain size container with a
'specific' product; two things must be known: (1)the lethality of the microor-
ganisms which may cause spoilage; and (2)the manner of heat penetration in the
canned product. For non-acid foods the organism in question is Clostridium
botulinum and the thermal lethality of this organism is well documented. For acid
foods any number of other organisms become more important, some of which are
even more resistant than C. botulinum. All that remains is to determine the manner
of heat penetration into the product in the specific size container.

1. Install copper-constantan thermocouples into the sides of the can. The thermocouples
must be placed at the coldest point in the can. For heavy thick products, the coldest point
is the geometric center of the can. For very dilute water-like products, because of convec-
tion heating the cold point is below the geometric center of the can and is determined by
experimentation. As a general rule, with smaller cans (eg. 303 x 406) the cold point is
about 0.75 inch above the bottom, assuming the can is standing upright. For large
containers (like a No. 10) the cold point is about 1.5 inches above the bottom.

2. Fill two cans with each product, exhaust and seal in a closing machine. Place cans upright
into the retort and attach the thermocouple extension wires. Connect the other ends of the
wires to a data logger or multipoint recorder for temperature recording.

3. Set temperature controls on retort and begin the process. Note when steam was turned on
(mark on the chart paper or circle data logger time). Also note time when venting is
finished and when retort operating temperature RT is achieved, as measured by the
mercury-in-glass thermometer. [It is convenient to also use a stopwatch here to measure
the time between steam on and time when operating temperature is reached on the glass
therrmometer. This will be used later for determining adjusted 0.] Rapid heating products
should be scanned rapidly (every minute or so) while slower heating products can be
scanned at longer intervals. Continue heating until the can temperatures are within about
2 degrees of the retort temperature. Turn off steam (noting the time) and begin cooling

1
 cycle. When cans are about 100-120°F, open retort and remove.

4. Prepare a table of “time after steam on” versus can temperature in convenient time units.
For example, for conduction heated foods you might use 2, 4 or 8 minute increments. For
convection heated foods, you might use 0.5 or 1 minute increments. If there are two
samples of each product, just average the temperatures of the two samples at each time
reading. To determine the process timing points, you can use the times printed on the data
logger tape or, if using a multipoint recorder, you must determine the times using the chart
speed and the gage lines on the paper. For instance, if the chart speed was 15 inches per
hour and the chart gradations are 0.5 inch, then each gradation represents 2 minutes.
Time=0 is the point at which steam was turned on. The time at which the retort reaches
the operating temperature as indicated on the mercury-in-glass thermometer is the "come-
up time".

5. There are two ways of calculating the process time for a product: the graphical method;
and the formula method (SEE ATTACHMENT - for complete descriptions, and then
some!). We will use the formula method. The heat penetration data is plotted on 3 or 4
log cycle semi-log graph paper - 3 cycle paper is included as the last page of the
attachments or you may purchase semi-log paper at the book store - eg. National Brand
Engineering Form 12-183. Temperature (IN DEGREES F) is plotted on the log scale and
time (IN MINUTES) on the linear scale. Note: For plotting this data, the paper is inverted
(i.e. turned upside down) compared to the normal way semi-log paper is used. Start
numbering the log cycles on the Y-axis (on the left side) with the temperatures beginning
at the top line and continuing downward. See example listed as Fig. 1 in the attached
sheets. The very top line should be 1°F lower than the retort temperature. For example
if the RT=245/F then the first line would be 244/F. Proceed with temperatures downward
--- remember this is log paper so there will be a step change every 10 lines.
The lower linear time scale (X-axis) should begin in the lower left corner with time 0. On
the right hand side (Y2-axis), if not already printed for you[but upside down], number the
typical log values starting with 1.0 on the top line which represents 1°F below RT. Proceed
downward to 1000 for 3 log cycle paper. This axis represents degrees below retort
temperature. If the axes are labeled correctly then values on the left scale should be equal
to the retort temperature minus the values on the right scale directly across.
Plot the points from your table on the chart paper. Try to draw a line through the maze of
dots so that it is within 1 degree or so of all points. Hopefully the plot will be mostly a
straight line except for an initial lag in the first 5 minutes or so and a tail which trails off
upward or sideward near the end (you can disregard these points). You will need at least
6 to 10 points to get a reasonable estimate of the regression line. Some products exhibit
a broken curve heating in which two intersecting lines must be drawn through the points
(see Fig. 2 in attached sheets). Pray that this does not happen for your product.
We need to get two data points from this plot: j, the lag factor; and fh, the slope.

6. First determine "corrected 0 time". To do this you must find the total time it took for the

2
 retort to “come up” to the operating temperature from “time on”. Find the time on the X
axis which represents 0.60 of the total come-up time in the retort after steam-on (or
conversely 0.40 of the come-up time before steam-up). Draw a vertical line upward from
this point until it intersects the straight line you drew in step 5. The temperature at the
point of intersection can be read from the temperature scale at the left and this value is
subtracted from the retort operating temperature RT to get jI. Alternatively, jI can be read
directly from the scale on the right which is degrees below RT. The initial temperature of
the product in the can before retorting is IT. First calculate I = RT-IT, then calculate j = jI/I
from the jI of the graph and I from the previous calculation. The value j must be corrected
if cans are small and the product is a conduction heated type. To do this, multiply the
calculated value by the appropriate "Correction factors for j" found in the attached handout
= jcorrected.

7. To determine fh count the minutes required for the drawn regression line to pass through
one log cycle (change by a factor of 10 eg. from 10 to 100 or 5 to 50) of temperature on the
left scale. Remember this is 3 log cycle paper.

8. To calculate the processing time we will assume C. botulinum is the problem organism and
we will want a desired value F250 or Fo=2.45 min. Find Fi for the actual operation
temperature [if not 250°F] used from table 4 in handout. Then calculate

(fh/U) = fh/ (Fo x Fi)

with this value of (fh/U) go to table 3 and find the value of log g corresponding to the fh/U.

9. The processing time (BB) in minutes is found by

BB = fh [log (jcorrected x I) - log g]

SOME CAUSES OF UNRELIABLE HEAT PENETRATION DATA

The following is a partial list of some factors that have been associated with unreliable heat
penetration data.

1. Thermocouple readings not continued for a sufficient length of time to adequately

define heating rate or rates.
2. Heat penetration test conducted in a retort load of commercial production and
stopped at the end of the scheduled process for quality determinations, rather than
continued long enough to obtain sufficient data.
3. Frequency of readings not sufficient to obtain accurate heating rate or rates.
4. Erroneous temperatures received as a result of inadequate electrical grounding of
potentiometer.
5. No initial temperatures taken on the test cans.
6. No notation of retort come-up time, or a come-up time significantly different from

3
 that used in commercial practice.
7. Multiple thermocouples in small cans of product.
8. No coldspot study, or insufficient number of replicates at the coldspot
thermocouple location.
9. No time notation on temperature recorder.
10. No notation of "steam on" for test.
11. No free lead reference.
12. No mercury thermometer readings.
13. Erratic processing temperature control during test.
14. Critical factors associated with product and processing system not recorded and
controlled.
15. Large temperature disagreement between thermocouple free lead and mercury
thermometer.
16. Initial temperature of test cans significantly different from that used in commercial
production.
17. In agitating retorts, rotation speed incompatible with commercial production.
18. No complete can-position study in rotating-cage retorts.
19. Excessive delay in running test after containers are sealed.
20. Product for tests not prepared according to procedures used commercially for raw
product preparation or condition.
21. Large difference in processing temperatures between heat penetration tests and
commercial practice.
22. One unexplained abnormally-slow-heating can within a group of cans.
23. Erratic and illogical thermocouple readings.
24. No readings taken until processing temperature is reached.

DISCUSSION QUESTIONS:
1. What are some factors which influence thermal resistance of micro-organisms?
2. What are some factors which influence heat penetration into a canned product?
3. How is thermal resistance determined?

4
 ATTACHMENT
Plotting Heat Penetration Curve
Heat penetration data are usually plotted on three cycle semilogarithmic paper. Temperature is represented on the logarithmic scale
and time on the linear scale. If the graph paper is inverted, the temperatures can be plotted directly as shown in Figure 1 for a straight
line heating curve and in Figure 2 for a broken heating curve.
The temperatures should be numbered from the top down starting with 1E be low the retort temperature. The time divisions should
be numbered from left to right starting with 0 and ending with the time at which the test was ended.
Plot the temperatures for the corresponding time. Inspect the data plotted. Simple heating curves consist of a lower portion which
rises slowly in temperaturetime. This is the lag when the container outside is heating rapidly but the product in the cold zone is not
receiving heat. When the product in the cold zone begins to receive heat, the temperature rises logarithmically. For straight convection
or conduction heating products, a single straight line can be drawn to the data points. This fine is known as the heat penetration curve.

PROCESS CALCULATIONS
The symbols used here are consistent with those used in the industry for many years. it is assumed that time and temperature data
have been obtained by heat penetration tests or that heat penetration factors for the product involved are available. Values for the
parameters m+g and z have been taken as 180EF and 18EF, respectively. All tables and graphs are based on these values. See definition
of terms and symbols at end of this chapter.

Methods of Analyzing Data

After time and temperature data for a given product in a given can size have been obtained by heat penetration studies, these data
may be analyzed by either of two methods:
(1)The "general" or "graphical" method.
(2)The "formula" method.
The two methods of determining process times or levels are based on identical principles but the mechanics or procedures used are
different. Each method has its own advantages. The choice of methods may be governed by the following conditions:
The graphical method is used when it is desired to measure the exact sterilizing value of a process, when such conditions as come-up
time, cooling water temperature, or the holding time after processing but before water cooling are different from normal retorting
procedures. This method is also adapted to conditions when the heat penetration curve cannot be represented by one or two straight lines
within the lethal temperature range on semi-logarithmic paper. It is not readily adapted to the calculation of processes when the retort
temperature and/or initial temperature are different from those under which the heating data were obtained. Time and temperature data
during the cooling cycle as well as the heating cycle must be recorded in order to use the graphical method. The graphical method is
not applicable to air cooled products.
The formula method is used when the heat penetration curve can be represented by not more than two straight lines on semi-
logarithmic paper. The formula permits evaluating processes for retort and initial temperature conditions differing from those under
which the heating data were obtained. In the case of heating curves represented by one line only on semi-log paper, the heat penetration
factors can be converted to different can sizes. The various methods of calculating processes win be described in detail.
Standards
It is first necessary to set up a standard sterilizing value. The greatest interest in processing canned foods is with low-acid products.
With such foods, 250EF has been generally established as the reference temperature and the lethal heat expressed in terms of minutes
at 250EF. This reference temperature will be used here.

The Graphical or General Method

As mentioned above, the lethal heat of a process is expressed in minutes at 250 degrees F. One minute at 250 degrees F or an
equivalent amount of heat is defined as one unit of sterilizing value. The symbol for sterilizing value is Fo.
Temperatures other than 250EF have lethal heat. Under conditions used here. one minute at 250EF is equivalent to 10 minutes at
232EF or 100 minutes at 214EF. In other words. for each 18E drop in temperature the time necessary to obtain the equivalent bacterial
destruction increases ten times.
The lethal ratio (Fo/t) or the sterilizing value effective in one minute at other temperatures (T) can be expressed mathematically as:

1
F0 '
(250& T)
log& 1
(18)

Lethal rate values in the range 200EF to 260EF are shown in Table 1.

5
6
7
 Table 1
LETHAL RATES
(For z equals 18)
TEMP (tenths of degrees F)
°F. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

190 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.001 0.001
191 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
192 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
193 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
194 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

195 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
196 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
197 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
198 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
199 0.001 0.001 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002

200 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002
201 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002
202 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002
203 0.002 0.002 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003
204 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003

205 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.004 0.004
206 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004
207 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.005 0.005
208 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005
209 0.005 0.005 0.005 0.005 0.006 0.006 0.006 0.006 0.006 0.006

210 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.007 0.007 0.007
211 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.008 0.008
212 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.009 0.009
213 0.009 0.009 0.009 0.009 0.009 0.009 0.010 0.010 0.010 0.010
214 0.010 0.010 0.010 0.010 0.011 0.011 0.011 0.011 0.011 0.011

215 0.011 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.013 0.013
216 0.013 0.013 0.013 0.013 0.014 0.014 0.014 0.014 0.014 0.014
217 0.015 0.015 0.015 0.015 0.015 0.016 0.016 0.016 0.016 0.016
218 0.017 0.017 0.017 0.017 0.018 0.018 0.018 0.018 0.018 0.019
219 0.019 0.019 0.019 0.020 0.020 0.020 0.020 0.021 0.021 0.021

220 0.022 0.022 0.022 0.022 0.023 0.023 0.023 0.024 0.024 0.024
221 0.024 0.025 0.025 0.025 0.026 0.026 0.026 0.027 0.027 0.027
222 0.028 0.028 0.029 0.029 0.029 0.030 0.030 0.030 0.031 0.031
223 0.032 0.032 0.032 0.033 0.033 0.034 0.034 0.035 0.035 0.035
224 0.036 0.036 0.037 0.037 0.038 0.038 0.039 0.039 0.040 0.040

225 0.041 0.041 0.042 0.042 0.043 0.044 0.044 0.045 0.045 0.046
226 0.046 0.047 0.048 0.048 0.049 0.049 0.050 0.051 0.051 0.052
227 0.053 0.053 0.054 0.055 0.056 0.056 0.057 0.058 0.058 0.059
228 0.060 0.061 0.062 0.062 0.063 0.064 0.065 0.066 0.066 0.067
229 0.068 0.069 0.070 0.071 0.072 0.073 0.074 0.075 0.075 0.076

230 0.077 0.078 0.079 0.080 0.081 0.083 0.084 0.085 0.086 0.087
231 0.088 0.089 0.090 0.091 0.093 0.094 0.095 0.096 0.097 0.099
232 0.100 0.101 0.103 0.104 0.105 0.107 0.108 0.109 0.111 0.112
233 0.114 0.115 0.117 0.118 0.120 0.121 0.123 0.124 0.126 0.128

8
 234 0.129 0.131 0.133 0.134 0.136 0.138 0.139 0.141 0.143 0.145

235 0.147 0.149 0.151 0.153 0.154 0.156 0.158 0.161 0.163 0.165
236 0.167 0.169 0.171 0.173 0.176 0.178 0.180 0.182 0.185 0.187
237 0.190 0.192 0.194 0.197 0.200 0.202 0.205 0.207 0.210 0.213
238 0.215 0.218 0.221 0.224 0.227 0.230 0.233 0.236 0.239 0.242
239 0.245 0.248 0.251 0.254 0.258 0.261 0.264 0.268 0.271 0.275

240 0.278 0.282 0.285 0.289 0.293 0.297 0.300 0.304 0.308 0.312
241 0.316 0.320 0.324 0.329 0.333 0.337 0.341 0.346 0.350 0.355
242 0.359 0.364 0.369 0.373 0.378 0.383 0.388 0.393 0.398 0.403
243 0.408 0.414 0.419 0.424 0.430 0.435 0.441 0.447 0.452 0.458
244 0.464 0.470 0.476 0.482 0.489 0.495 0.501 0.508 0.514 0.521

245 0.527 0.534 0.541 0.548 0.555 0.562 0.570 0.577 0.584 0.592
246 0.599 0.607 0.615 0.623 0.631 0.639 0.647 0.656 0.664 0.673
247 0.681 0.690 0.699 0.708 0.717 0.726 0.736 0.745 0.755 0.764
248 0.774 0.784 0.794 0.805 0.815 0.825 0.836 0.847 0.858 0.869
249 0.880 0.891 0.903 0.914 0.926 0.938 0.950 0.962 0.975 0.987

250 1.000 1.013 1.026 1.039 1.053 1.066 1.080 1.094 1.108 1.122
251 1.136 1.151 1.166 1.181 1.196 1.212 1.227 1.243 1.259 1.275
252 1.292 1.308 1.325 1.342 1.359 1.377 1.395 1.413 1.431 1.449
253 1.468 1.487 1.506 1.525 1.545 1.565 1.585 1.605 1.626 1.647
254 1.658 1.690 1.711 1.733 1.756 1.778 1.801 1.824 1.848 1.872

255 1.896 1.920 1.945 1.970 1.995 2.021 2.047 2.073 2.100 2.127
256 2.154 2.182 2.210 2.239 2.268 2.297 2.326 2.356 2.387 2.417
257 2.448 2.480 2.512 2.544 2.577 2.610 2.644 2.678 2.712 2.747
258 2.783 2.818 2.855 2.891 2.929 2.966 3.005 3.043 3.082 3.122
259 3.162 3.203 3.244 3.286 3.328 3.371 3.415 3.459 3.503 3.548

260 3.594 3.640 3.687 3.734 3.782 3.831 3.881 3.930 3.981 4.032
261 4.084 4.137 4.190 4.244 4.299 4.354 4.410 4.467 4.524 4.583
262 4.642 4.701 4.762 4.823 4.885 4.948 5.012 5.076 5.142 5.208
263 5.275 5.343 5.412 5.481 5.552 5.623 5.696 5.769 5.843 5.919
264 5.995 6.072 6.150 6.229 6.310 6.391 6.473 6.556 6.641 6.726

265 6.813 6.901 6.989 7.079 7.171 7.263 7.356 7.451 7.547 7.644
266 7.743 7.842 7.943 8.046 8.149 8.254 8.360 8.468 8.577 8.687
267 8.799 8.913 9.027 9.143 9.261 9.380 9.501 9.624 9.747 9.873
268 10.000 10.129 10.259 10.391 10.525 10.661 10.798 10.937 11.078 11.220
269 11.365 11.511 11.659 11.809 11.961 12.115 12.271 12.429 12.589 12.751

270 12.915 13.082 13.250 13.421 13.594 13.769 13.946 14.125 14.307 14.491

At the slowest heating point within the container. there is a gradual rise in the temperature. the rate being dependent on the physical
characteristics of the product. There will be some lethal effect during each minute of the process; the amount during this interval is
dependent upon the temperature at that time. These values are obtained from Table 1 and they can be added to obtain the total effective
lethal heat of the process.
Heat penetration time and temperature data are usually recorded at some convenient time interval and can be set up in four columns
as shown in Table 2. In the third column is added the sterilizing value effective in one minute (lethal rate) at the temperature indicated.
The sum of Fo values in the third column will be the sterilizing value of the process if the temperature observation had been made of each
minute of the process. When temperature observations are not made each minute of the process. lethal rate values must be extrapolated
from the known Fo per minute values. as shown in the fourth column.

9
 TABLE 2 HEAT PENETRATION DATA
CONDUCTION HEATING - 211 x 304 CAN
Come-Up Time: 10 minutes Retort Temperature: 240EF
Heating time Temperature Lethal Rate 3 F0/min Cooling time Temperature Lethal Rate 3 F0/min
IT 160 0 71 237.8 0.21 0.21

6 164 0 72 235.9 0.165 0.165

12 174 0 73 232.7 0.109 0.109

18 195 0.001 0.003 74 228.7 0.066 0.066

21 201 0.002 0.006 75 223.8 0.035 0.035

24 208 0.005 0.015 76 218 0.017 0.017

27 214 0.01 0.03 77 212 0.008 0.008

30 218.5 0.017 0.058 78 206 0.004 0.004

33 222.5 0.028 0.084 79 199 0.001 0.001

36 225.5 0.041 0.123 80 192 0.001 0.001

39 228 0.06 0.18 85 157 0 0

42 230 0.077 0.231 90 132 0 0

45 232 0.1 0.3 95 115 0 0

48 233.5 0.121 0.363 100 102 0 0

51 234.6 0.138 0.414 105 94 0 0

54 235.3 0.153 0.459 0.616

57 236.4 0.176 0.528

60 237 0.19 0.57

63 237.6 0.205 0.615 Heating time F0 = 5.089

66 238 0.215 0.645 Cooling time F0 = 0.616

69 238.4 0.227 0.227 Process F0 = 5.705

70 238.5 0.23 0.23

70 steam off 5.089

The lethal rate figures can be plotted against time on coordinate paper to obtain a lethal rate curve as shown in Figure 3. Since the
vertical distance on this curve at each minute represents the F0 effective in that minute. it follows In other words. the sterilizing value
is proportional to the area under the curve. that the total sterilizing value is equal to the sum of all the vertical distances for every minute
of the process. It is necessary to measure the area under the curve in order to determine process sterilizing value. This can be done
by Simpson's rule. or with method of counting the small squares or with an instrument called a planimeter. The area in square inches
must be multiplied by a factor to be converted to Fo units. This factor is found by determining the area of a unit sterilization area such
as ABCD shown in Figure 3.
The product of the height and width of this area in terms of F0 per minute and time is unity. The factor to be multiplied by the
square inch area under the lethal rate curve is the reciprocal of the square inch area of the unit sterilization rectangle. This means that
if the area under the curve is 6.5 square inches. Fo equals 6.5 divided by 0.5 equals 13.
The procedure for determining the length of a process for a known sterilizing value is quite similar except that instead of measuring
area for a known length of process. the process is found to yield a known area under the curve. For example. suppose a process is wanted
having a sterilizing value of 10. previous experience having shown that this value gives satisfactory results. It is necessary then to find
the time that would yield an area of 5 square inches under the lethality curve. Inspection of the curve would lead us to believe that this
time would not be far from 65 minutes. We will. therefore. estimate the cooling curve from 65 minutes which we can do fairly accurately
by drawing it parallel to the actual cooling curve from 78 minutes. Now. we will measure the area under this 65 minute curve by one
of the methods previously described. and we find it to be 4.56 square inches. Since this process fails to give us 5 square inches. or 10
Fo units under the curve. we know that 65 minutes is not quite enough. Actually. we need not go further than this as it is almost a

10
certainty that the next higher practical process. i.e.. 70 minutes. would yield at least 5 square inches. We check these though. and find

the area under the 70 minute curve to be 5.85 square inches or 11.7 Fo units. We could of course. interpolate between 65 and 70 minutes
to get a more exact time. but for practical purposes we will select 70 minutes.
It should be emphasized again that the results obtained by this method are valid only when the initial and retort temperature
conditions are the same as those of the heat penetration tests. If the heat penetration curve can be represented by one or two straight lines
on semi-log paper. it is possible to make corrections for these factors. but in this case. the graphical method is not the recommended one.
Either the formula method or the nomogram method is better suited for such a calculation.

Effect of 3 Degrees F Errors in Retort Temperature on

Fo Value of Heating Phase of Typical Processes
for 303 x 406 Cans

Initial Process Retort

Product Temp. Time Temp. Fo
(°F) (min) (°F) (min)

Green beans 120 20 237 2.0

in brine 240 3.0
243 4.7

Cream-style 140 95 237 3.2

corn 240 4.4
243 6.2
The Formula Method
The first step in calculating processes by the formula method is to plot the time-temperature data on semi-log paper. time being
plotted as abscissae and temperature as the logarithmic ordinate. Zero time is the time at steam on. The time at which the retort reaches
processing temperature is noted as come-up time. Three cycle semi-log paper generally provides a convenient range for plotting the data.
Actually. the temperatures plotted are the retort temperature minus the can temperature. Instead of making these subtractions it is
more practical to turn the semi-log paper upside down and plot can temperatures directly. The temperature on the top line is one degree
below retort temperature. At the bottom of the first log cycle the temperature is 10 degrees below retort temperature and at the bottom
of the second log cycle. 100 degrees below.
Either one straight line (simple heating curve) or not more than two straight lines (broken heating curve) are drawn through the
points in the lethal temperature range (above 210EF). An attempt should be made to pass the straight lines within 1 degree of all the
points rather than fit them by any geometric mean method.
Having drawn the lines on the graph paper. factors must be determined that will describe the positions. Simple and broken heating
curves will be discussed separately.

11
Simple Heating Curve
A plot of a simple heating curve is shown in Figure 1. From this plot we obtain two factors used in calculating processes. These
factors are j (lag factor) and fh (slope).
In making a heat penetration test. some time is required in bringing retort to processing temperature. It will be obvious that the
come-up time does not have the heating value of the processing or holding temperature but that its heating value would be more than
0 minutes. Conventionally. the heating value of the come-up me is taken as 0.42 of the come-up time. This means the corrected
beginning of process is not when the retort reaches process temperature but 0.4 of the come-up time before steam-up or 0.6 of the come-up
time after steam-on. With a 10 minute come-up. the corrected 0 is at 6 minutes on the time scale. It is necessary make this correction
because retort come-up times will vary over comparatively wide limits and. unless means are provided for correcting these to the come-up
time will always have to be specified with the heat penetration curve. If because of the long come-up time it is necessary to make
allowance for come-up 0.4 of the come-up can be subtracted from the calculated process or the sterilizing value is the sought unknown
0.4 of the come-up time is added to process time.
Having determined the corrected zero time. a vertical line is drawn at this value on the time scale and crossing the extended straight
line drawn through the time-temperature plotted. The point where these two lines cross will be a certain number of degrees below the
retort temperature and this value is called "jI". A temperature value can be read on the left side temperature scale corresponding to the
point the lines cross and this value subtracted from the retort temperature. If a degree-below-retort-teperature scale is marked on the right
hand side of the graph paper, the value of "jI" can be read from this scale directly.
(1) I = RT-IT
The retort temperature (RT) is the retort temperature obtained during the heat penetration test. and the initial temperature (IT) is
the center temperature of a particular can for which the time_temperature data are plotted.
Then:
(2) j = jI/I
Thiss value of j remains constant for the given product; it does not change when converting the heating data to another can size.
With smaller cans of conduction heating products. a correction to the j value is advisable to compensate for heat conducted into the
product by the thermocouple wires and fittings. These corrections are discussed by Ecklund in his article. "Correction Factors for Heat
Penetration Thermocouples". (Food Technol. 10:43-44. 1956). The following table gives correction factors for j.

12
 Correction factors for “j”
Use on conduction heating products only
Can Size Multiply "j" factor by:

202 x 214 1.36

211 x 400 1.16
300 x 407 1.10
307 x 409 1.06

The second heat penetration factor obtained from the graph of a simple heating curve is fh. This factor is the time in minutes for
the straight line drawn through the time-temperature plots to pass through one logarithmic cycle. A log cycle is the distance between
any two points on the logarithmic ordinate in which the number of degrees below retort temperature increases ten times. For example.
the distance can be from 1 to 10. 3 to 30. 10 to 100 or 20 to 200 as read on the right hand side of the graph sheet.
With the values of j and fh obtained from the graph of the heating data. the sterilizing value (Fo) of a process can be determined or
the process time in minutes (BB) can be calculated for a desired Fo value.

To calculate Fo we use the following equations:

BB
(3) log g = log jI −
fh

fh
(4) Fo =
(fh / U)Fi

In equation (3) the values of j and fh have already been determined. BB (process time) is known and I = RT-IT. RT is a retort
temperature at which the product will be processed and IT is the initial temperature that will be encountered under commercial canning
conditions. These values are substituted in equation (3) and the value of "log g" calculated. The value of "g" is the number of degrees
below retort temperature at the slowest heating point in the container at the end of the process. In order to simplify calculations. the log
g is used in the equations.
For each value of log g there is a corresponding value of the term fh/U. This relationship is shown in Table 3. The term "Fi" is
related to the retort temperature. It can be calculated by the equation:

−1  ( 250 − RT) 
(5) Fi = log  
18

Values of Fi for various retort temperatures are listed in Table 4.

The proper value of Fi for the retort temperature is selected and substituted in equation (4) along with fh/U (found from Table 5 for
the corresponding value of log g) and fh. The Fo value obtained will be the sterilizing value of the process.

To calculate BB we use the following equations:

fh
(6) fh / U =
Fo × Fi

(7) BB = fh (log jI − log g )

In equation (6). fh is from the heat penetration curve. Fo is the desired sterilizing value and Fi is obtained from Table 4 for the
particular retort temperature involved. With these values. fh/U is calculated. From the relationship of fh/U and log g shown in Table 3.
the value of log g can be found which corresponds to the value of fh/U calculated in equation (6).
This value of log g is substituted in equation (7). The values of j and fh are from the heat penetration curve and I again is RT-IT.
The value of BB calculated would be the process time in minutes.

13
 TABLE 4
Fi VALUES FOR VARIOUS RETORT TEMPERATURES (°F.)
RT Fi RT Fi RT Fi
214 100.00 233 8.799 252 0.7743
215 87.99 234 7.743 253 0.6 813
216 77.43 235 6.813 254 0.5995
217 68.13 236 5.995 255 0.5275
218 59.92 237 5.275 256 0.4642
219 52.75 238 4.642 257 0.4085
220 46.42 239 4.085 258 0.3594
221 40.85 240 3.594 259 0.3163
222 35.94 241 3.163 260 0.2783
223 31.63 242 2.783 261 0.2449
224 27.83 243 2.449 262 0.2154
225 24.48 244 2.154 261 0.1896
226 21.54 245 1.896 264 0.1668
227 18.96 246 1.668 265 0.1468
228 16.68 247 1.468 266 0.1292
229 14.68 248 1.292 267 0.1136
230 12.92 249 1.136 268 0.1000
231 11.36 250 1.000 269 0.0880
232 10.000 251 0.8799 270 0.0774

13
1000

100

10

1
 HP_protocol

Institute For Thermal Processing Specialists

PROTOCOL FOR CARRYING OUT HEAT PENETRATION STUDIES

Various methods and equipment may be employed in order to collect accurate heat penetration data. The
overall objective of these guidelines is to recommend procedures for carrying out heat penetration studies
for establishing thermal processes necessary to produce commercially sterile foods packaged in
hermetically sealed containers. The following recommendations are to be considered voluntary guidelines.
While this does not preclude the application of other methods and equipment for collecting heat
penetration data, these guidelines have been developed by consensus of the Institute for Thermal
Processing Specialists and should be given serious consideration for adoption as methodology by
individuals performing heat penetration studies.

1. NOMENCLATURE

t - Time

tc - Retort come-up time is the time between the start of heating and the time when the retort
reaches processing temperature (at times referred to as CUT)

tp - Process time is the time from the end of the come-up period to the end of heating (at
times referred to as the operator's process time)

T - Temperature

Tc - Container center or coldspot temperature (at times referred to as CT)

Tr - Retort temperature (at times referred to as RT)

Tw - Cooling water temperature (at times referred to as CW)

2. TERMINOLOGY

2.1 Ballast Containers: Containers may be required to fill the retort during heat penetration
studies to simulate production retort conditions. Type, shape and size of containers should be
the same as used for the intended process. Material used for filling containers could be the

file:///C|/iftps/protocols/hp_protocol.htm (1 of 15)6/5/2004 8:27:21 AM

 HP_protocol

test product, or any suitable material having heating characteristics similar to that of the test
product, or in some circumstances, water.

2.2 Cooling Time: Time required following the introduction of the cooling medium to
decrease the internal temperature of the product to a specified value, commonly 35 to 45o C
(95 - 110o F).

2.3 Critical Factors: Physical and chemical factors that can influence the thermal response
of a product to a thermal process, the variation of which may influence the scheduled
process, including: container, product, retort and processing conditions.

2.4 Fill, Drain and Net Weights: Fill weight is the weight of solids prior to processing; drain
weight, the weight of solids after processing; and net weight, the weight of all product in a
container

2.5 Heat Penetration Curve: Plot of the logarithmic difference between either retort
temperature and product temperature (heating curve) or product temperature and cooling
medium temperature (cooling curve) versus time.

2.6 Mercury-in-Glass Thermometer (MIG): Generally used as the retort reference

temperature device and regulated for that application by government agencies in some
countries. Other temperature measuring devices may be calibrated against a MIG retort
thermometer which has been calibrated against a traceable temperature standard.

2.7 Resistance Temperature Detector (RTD): Thermometry system based on the positive
change in resistance of a metal sensing element (commonly platinum) with increasing
temperature

2.8 Temperature Measuring Device (TMD): Device used for measuring temperature,
including: thermometers, thermocouples, RTDs and thermistors.

2.9 Thermistor: TMD manufactured from semiconductor materials which exhibits large
changes in resistance proportional to small changes in temperature. Thermistors are more
sensitive to temperature changes than thermocouples or RTDs and are capable of detecting
relatively small changes in temperature.

2.10 Thermocouple: TMD composed of two dissimilar metals which are joined together to
form two junctions. When one junction is kept at an elevated temperature as compared to the
other, a small thermoelectric voltage or electromotive force (emf) is generated which is
proportional to the difference in temperature between the two junctions.

3. DESIGN OF A HEAT PENETRATION STUDY

The purpose of a heat penetration study is to determine the heating and cooling behavior of a
product/package combination in a specific retort system for the establishment of safe thermal

file:///C|/iftps/protocols/hp_protocol.htm (2 of 15)6/5/2004 8:27:21 AM

 HP_protocol

processes and evaluating process deviations. The study must be designed to adequately and
accurately examine all critical factors associated with the product, package and process which
affect heating rates. Numbers of containers per test run, and number of test runs to account for
statistical variability are important and discussed in sections 5.11 and 5.12. Before commencing a
heat penetration study, an evaluation of retort temperature and heat transfer uniformity, at times
referred to as a heat or temperature distribution study (IFTPS, 1992), should have been completed.
A goal in conducting these studies is to identify the worst case temperature response expected to
occur in commercial production as influenced by the product, package and process.

4. FACTORS AFFECTING HEATING BEHAVIOR

Several product, process, package and measurement related factors can contribute to
variations in the time-temperature data gathered during a heat penetration test.
Establishment of a process requires expert judgment and sound experimental data for
determining which factors are critical and the effect of changing those factors both within and
beyond established critical limits. The list of items addressed in this section is extensive, but
should not be assumed to cover all possible factors. Quantitative data on variability should be
recorded where appropriate and all pertinent data should be documented to better
understand and account for possible variations in heat penetration behavior.

4.1 Product:

4.1.1 Product formulation and weight variation of ingredients should be

consistent with worst case production values. Changes in formulation may
necessitate a new heat penetration study.

4.1.2 Fill weight used for heat penetration studies should not be less than the
maximum declared on the process schedule. Excess product may be expressed
as percent overfill.

4.1.3 Solids content should be measured for nonhomogeneous products both

before and after processing. Solids content deposited in a sieve should be
weighed and expressed as a percentage of total weight. Note: Addition of
compressed or dehydrated ingredients may result in increased drained weight.

4.1.4 Consistency or viscosity of semi-liquid or liquid components should be

measured before and after processing. Flow behavior will change with type and
concentration of thickening agent (starch, gums, etc.), temperature and shear
rate. Changes may be reversible or irreversible which may be important when
reprocessing product.

4.1.5 Size, shape and weight of solid components should be measured before
and after processing.

4.1.6 Integrity and size of solid component clusters may change during

file:///C|/iftps/protocols/hp_protocol.htm (3 of 15)6/5/2004 8:27:21 AM

HP_protocol

processing and affect temperature sensor placement in the product and

coldspot location.

4.1.7 Methods of product preparation prior to filling should simulate commercial

practice. For example, blanching may cause swelling, matting or shrinkage
which could influence heat penetration characteristics.

4.1.8 Product matting or clumping may change heat penetration characteristics

and influence coldspot location. Also caution should be exercised with sliced
products which may stack together during processing.

4.1.9 Rehydration of dried components, either before or during processing, is a

critical factor which may influence heat penetration behavior, as well as process
efficacy with respect to spore inactivation. Details of rehydration procedures
should be recorded during the heat penetration study.

4.1.10 Product may heat by convection, conduction or mixed convection/

conduction depending on its physical properties. Some foods exhibit complex
(broken) heating behavior. Product may initially heat by convection, then due to
a physical change in the product, change to conduction heating behavior. For
example, for products such as soups which contain starch, the change in
heating behavior may be due to starch gelatinization at a particular temperature.
Small variations in product formulation or ingredients may cause the transition
from convection to conduction heating to occur at a different temperature and
related time. Special care should be taken to identify and control specific
product and process variables related to the heating rates of these products.

4.1.11 Additional product characteristics such as salt content, water activity, pH,
specific gravity, concentration of preservatives, and methods of acidification
may influence heat transfer or microbiological resistance and should be
recorded.

4.2 Container:

4.2.1 Manufacturer and brand name information should be recorded in case

information related to filling, sealing or processing is required.

4.2.2 Container type (metal cans, glass jars, retort pouches, semi-rigid
containers), size and dimensions should be recorded.

4.2.3 Nesting of low profile containers can influence heating behavior. Heat
penetration studies on jumble loaded retorts (no racks or dividers) should
include tests conducted on stacks of nested cans as well as single cans.

file:///C|/iftps/protocols/hp_protocol.htm (4 of 15)6/5/2004 8:27:21 AM

HP_protocol

4.2.4 Container vacuum and headspace should be recorded for rigid containers.
For flexible and semi-rigid containers the volume of residual gases in the
container should be determined. Entrapped gases may create an insulating
layer in the container causing a shift in the coldspot location and a decrease in
the heating rate. Controlled overpressures during processing have been found
to reduce these effects.

4.2.5 Maximum thickness of flexible packages (pouches) has a direct

relationship to the coldspot temperature history with thicker packages heating
more slowly. Heat penetration studies should be carried out at the maximum
specified package thickness.

4.2.6 Container orientation (vertical or horizontal) within the retort may be a

critical factor for some product/package combinations and should be studied
where appropriate. Changes in container orientation may also influence vent
schedules and come-up time.

4.2.7 Postprocessing examination of test containers for abnormalities should be

conducted with special emphasis on the slowest and fastest heating containers.
It is strongly recommended that flexible packages be carefully examined
following processing to identify the thermocouple junction location. If the
intended sensing location has shifted, it is likely that heat penetration data
collected are not reliable.

4.3 Method of Fill:

4.3.1 Fill temperature of the product should be controlled. It will affect the initial
temperature which may influence some heat penetration parameters (lag factor,
retort come-up period). This may constitute a critical control point for a process,
particularly for products which exhibit broken heating behavior.

4.3.2 Fill and net weights may influence heating rates both in still and rotary
cooks. Information on variability may be found in statistical process control and
product quality control records.

4.3.3 In most cases, controlling headspace by determining net weight is not

sufficient due to possible variations in the specific gravity of the food product.
Care should be taken to avoid incorporation of air which would affect the
headspace vacuum. In rotary processes, container headspace is a critical
control point since the headspace bubble helps mix the product during agitation.

4.4 Closing or Sealing: Closing or sealing equipment should provide a strong, hermetic seal
which is maintained during the thermal process. Vacuum in cans and jars for most canned
foods is recommended to be between 35-70 kPa (10-20 in-Hg) measured at room
temperature. Vacuum is affected by variables such as: headspace, product temperature,

file:///C|/iftps/protocols/hp_protocol.htm (5 of 15)6/5/2004 8:27:21 AM

HP_protocol

entrapped air, and vacuum efficiency of the closing equipment. Some products such as
vegetables vacuum packed in cans may have a minimum vacuum as a critical control point.
For others packed in flexible or semi-rigid containers, vacuum setting will influence the
residual air content in the package, also constituting a critical control point.

4.5 Retort System: The type of retort system used may have a significant influence on
the heating rates of products processed in the retort. Results from a heat penetration
test should be reported with reference to the retort type and conditions existing at the
time of testing.

4.5.1 Retort come-up time should be as short as possible consistent with

obtaining satisfactory temperature distribution. Laboratory size retorts may be
used for development work on heat penetration behavior. Results will be
conservative when the smaller retorts have shorter come-up times and cool
more quickly than production retorts. After development, the thermal process
should, if physically possible, be verified in an appropriate production retort.

4.5.2 Racking systems may be used to separate layers of cans or jars; constrain
the expansion of semi-rigid and flexible containers; provide support and
circulation channels for thin profile containers; and ensure maximum pouch
thickness is not exceeded. Care should be taken to understand the influence of
a specific rack design on retort performance and heat transfer to containers.

4.5.3 Still batch retort systems vary in operation based on: type of heating
medium(steam, steam/air, water immersion, water spray); orientation of the
retort (vertical, horizontal); method of heating medium agitation (fans, pumps, air
injection); and other factors which may influence the heating behavior.

4.5.4 Rotational batch retort systems (axial, end-over-end) are designed to

rotate (or oscillate) entire baskets of product during processing. Container
agitation may provide faster rates of heat penetration to the container coldspot
as compared to still cooks. However, while this is true for some containers, it
may not be so for all containers within a load and caution must be exercised to
identify the slowest heating containers. This may entail a detailed can-position
study. It is recommended that during initial testing, data be collected at small
time increments (15 s) particularly for viscous fluids where the coldspot may
move in relationship to a fixed thermocouple during rotation, producing
erroneous results. Slip-ring connectors should be cleaned and thermocouple
calibration verified at regular intervals. Critical factors in these retorts include:
headspace, product consistency, solids to liquid ratio, initial temperature,
container size, rotational speed and radius of rotation.

4.5.5 Continuous retort systems may move containers through the processing
vessel along a spiral track located at the outside circumference of a horizontal
retort shell or be carried through a hydrostatic retort in chain driven flights.
Regardless of the configuration, it becomes difficult or impossible to use

file:///C|/iftps/protocols/hp_protocol.htm (6 of 15)6/5/2004 8:27:21 AM

 HP_protocol

thermocouples to collect heat penetration data in these systems. Data may be

obtained using self-contained temperature measurement and data storage
modules in the commercial vessel or by using process simulators.

5. TEMPERATURE MEASUREMENT AND DATA ACQUISITION

5.1 Data Acquisition System: Accuracy and precision of the data acquisition system
(datalogger) used for heat penetration studies will affect temperature readings. Dataloggers
are typically comprised of a multi-channel temperature measuring and digital data output
system. Calibration of a data acquisition system should include verification of the data
acquisition rate, since errors in the time base would result in erroneous data.

5.2 Type of Thermocouple: The most common TMDs used in thermal processing are
duplex Type T (copper/constantan) thermocouples with Teflon insulation. Common
configurations are flexible wires (20-, 22- or 24-gauge) and rigid needle types. Details on
thermocouples and connecting units are available in Bee and Park (1978) and Pflug (1975).

5.3 Type of Connectors and Associated Errors: Connectors used in a thermocouple

circuit are fittings attached to a thermocouple within which electrical connections are made.
Several types of connectors are available for specific applications and thermocouple type.
Caution must be exercised to avoid certain sources of error which may be associated with
the use of connectors and extension wires. These include: disparity in thermal emf between
thermocouples, connectors and extension wires; temperature differences between two wire
junctions; and reversed polarity at the thermocouple-extension wire junction. Thermocouple
connectors should be cleaned frequently with metal cleaner to assure good electrical contact
and prevent errors in thermocouple readings. Similar concerns should be addressed when
using RTDs and thermistors.

5.4 Thermocouple Calibration: Thermocouples should be calibrated against a traceable

calibration standard (thermometer, RTD, thermistor). Inaccuracies in temperature
measurements may result in errors in process evaluation; hence, frequent calibration is
essential to provide reliable data. Factors affecting calibration include: worn or dirty slip-rings,
improper junctions, metal oxidation, multiple connectors on one lead, and inadequate
datalogger cold junction compensation. As a consequence, thermocouples should be
calibrated in place as part of the complete data acquisition system. Some precautions when
using thermocouple based data acquisition systems include: minimizing multiple connections
on the same wire; cleaning all connections; grounding the thermocouples and recording
device; slitting thermocouple outer insulation outside the retort to prevent flooding of
datalogger or data recording device (see NFPA, 1985, or ASTM, 1988 for illustrations); and
using properly insulated thermocouple wires.

5.5 Positioning of Thermocouple in the Container: The method of inserting a

thermocouple into a container should result in an airtight, watertight seal which should be
verified after testing. Thermocouple sensing junctions should be positioned in the slowest
heating component of the food product and situated in the slowest heating zone within the
container. During insertion of the thermocouple, caution must be taken to avoid physical

file:///C|/iftps/protocols/hp_protocol.htm (7 of 15)6/5/2004 8:27:21 AM

HP_protocol

changes to the product. Also, the method employed for mounting the thermocouple into the
container should not affect the container geometry which could influence heat penetration
characteristics. Flexible or rigid thermocouples may be inserted into rigid, flexible and semi-
rigid containers using compression fittings or packing glands. For flexible containers, NFPA
(1985) provides illustrations of thermocouple positioning into a solid particulate and several
thermocouple positioning devices to ensure the thermocouple remains in a fixed position
within the container. The most appropriate device for a particular application will depend
upon the product, racking system, container type and sealing equipment. Leakage may be
detected by weighing the container before and after processing to determine changes in
gross weight. If there is leakage caused by improperly mounted thermocouples, data
collected for that container should be discarded. Note: Ecklund (1956) reported correction
factors for heat penetration data to compensate for errors associated with the use of
nonprojecting, stainless steel receptacles. While not reported in the literature, this may also
be a concern with other fittings.

5.6 Type and Placement of Containers: The type and size of container used in the heat
penetration study should be the same as that used for the commercial product. The racking
and loading of rigid (cans), semi-rigid (trays and cups) and flexible (pouches) containers
should simulate commercial practice. Test containers should be placed at the slowest heating
location in the retort, as determined by temperature and heat transfer distribution studies.

5.7 Temperature of the Heating Medium: TMDs should be positioned so as to prevent

direct contact with racks or containers and identified according to their specific location in the
retort. A minimum of two thermocouples is recommended for retort temperature
measurement: one situated close to the sensing bulb of the retort MIG thermometer, the
other located near the test containers. In addition, at least one thermocouple should be
placed near the sensor for the temperature controller when that location is remote from the
location of the MIG thermometer bulb.

5.8 Retort Pressure: Overpressure conditions during processing will influence package
expansion by constraining the expansion of headspace gases. This may be beneficial by
improving heat transfer to food in flexible and semi-rigid containers or detrimental by
restricting the size of the headspace bubble in rotary processes. For steam/air retorts,
overpressure conditions are also related to the steam content of the heating medium at a
particular processing temperature which may influence heat transfer conditions within the
retort. In addition, cooling without overpressure may result in depressurization within a
container upon collapse of steam at the end of a process, leading to accelerated decreases
in temperature for fluid foods.

5.9 Coldspot Determination: The location of the slowest heating or coldspot in a container
is critical to establishing a process. For a conduction heating product in a cylindrical can with
minimal headspace, the geometric center of the can is considered to be the slowest heating
spot. Generally, if a larger headspace is included, the coldspot may shift closer to the top of
the can due to the insulating effect of the headspace which may be significant if the height-to-
diameter ratio of the can is small. The coldspot location in vertically oriented cylindrical cans
containing products which heat by natural convection may be near the bottom of the

file:///C|/iftps/protocols/hp_protocol.htm (8 of 15)6/5/2004 8:27:21 AM

 HP_protocol

container. Products which exhibit broken heating behavior may have a coldspot which
migrates during heat processing as the physical properties of the product change. The use of
containers with different geometries or constructed from different materials may have
differing effects on coldspot locations. A coldspot location study should be completed to
determine the slowest heating location for a specific product/package/process combination.
Usually, the coldspot location will be determined from a series of heat penetration tests
employing several containers with thermocouples inserted at different locations. Alternatively,
more than one thermocouple per container may be used; however, multiple thermocouples
may influence heating behavior, especially for products in smaller containers. In all cases,
care should be taken to determine the "worst case" anticipated during production. Careful
judgment, based on a number of preliminary experiments, must be exercised to ensure the
coldspot location has been identified.

5.10 Initial Product Temperature: Measurement of initial product temperature should be

taken immediately prior to testing.

5.11 Number of Containers per Test Run: A heat penetration test should evaluate at least
10 working thermocouples from each test run (NFPA, 1985). If the retort cannot
accommodate this quantity, the number of replicate test runs should be increased.

5.12 Number of Test Runs: Replication of heat penetration test runs is important in order to
obtain results which account for run-to-run, product, container and process variability. After
initial coldspot determination tests are completed and all critical factors have been
determined, at least two full replications of each test are recommended. Should results from
these tests show variation, a minimum of a third test is recommended. Variation in the results
is expected and quite common, especially for products which are non-homogeneous or
exhibit complex heating behavior. Variability is generally evaluated based on plots of the
heating and cooling curves and/or lethality calculations and should be considered when
identifying or predicting the slowest heating behavior of a process.

6.0 SUMMARY OF DOCUMENTATION

The following provides a summary of details which may be incorporated in a checklist and
documented in their entirety or partially as deemed appropriate for a specific study. Other
factors not listed in this section may also be relevant.

6.1 Pre-test Documentation:

6.1.1 Product Characteristics 6.1.1.1 Product name, form or style, and packing
medium

6.1.1.2 Product formulation and weight distribution of components

6.1.1.3 Net weight and volume

file:///C|/iftps/protocols/hp_protocol.htm (9 of 15)6/5/2004 8:27:21 AM

HP_protocol

6.1.1.4 Consistency or viscosity of the liquid component

6.1.1.5 Size, shape and weight of solid components

6.1.1.6 Size of solid component clusters

6.1.1.7 pH of solid and liquid components

6.1.1.8 Methods of preparation prior to filling (ingredient mixing methods, special

equipment)

6.1.1.9 Matting tendency

6.1.1.10 Rehydration of components

6.1.1.11 Acidification procedures

6.1.1.12 Other characteristics (% solids, density, etc.)

6.1.2 Container Description

6.1.2.1 Container material (brand name and manufacturer)

6.1.2.2 Type, size and inside dimensions

6.1.2.3 Container test identification code

6.1.2.4 Maximum thickness (flexible container)

6.1.2.5 Gross weight of container

6.1.2.6 Container nesting characteristics

6.1.2.7 Slowest heating or coldspot location in container

6.1.3 Data Acquisition Equipment and Methodology

6.1.3.1 Identification of datalogging system

6.1.3.2 Thermocouple and connector plugs maintenance

file:///C|/iftps/protocols/hp_protocol.htm (10 of 15)6/5/2004 8:27:21 AM

HP_protocol

6.1.3.3 Thermocouples and connectors numbered

6.1.3.4 Electrical ground checked

6.1.3.5 Thermocouples placed in heating medium and readings compared with

a reference TMD

6.1.3.6 Type, length, manufacturer and identification code of thermocouples and

connectors

6.1.3.7 Thermocouple location in container

6.1.3.8 Positioning technique for thermocouple

6.1.3.9 Calibration data for each thermocouple

6.1.4 Fill Method

6.1.4.1 Fill temperature of product

6.1.4.2 Fill weight of product

6.1.4.3 Headspace

6.1.4.4 Filling method (comparison to commercial process)

6.1.5 Sealing Operations

6.1.5.1 Type of sealing equipment

6.1.5.2 Time, temperature, pressure and vacuum settings (if applicable)

6.1.5.3 Gas evacuation method

6.1.5.4 Can vacuum

6.1.5.5 Volume of residual gases in flexible containers

6.1.6 Retort System

file:///C|/iftps/protocols/hp_protocol.htm (11 of 15)6/5/2004 8:27:21 AM

HP_protocol

6.1.6.1 Retort system: still or rotary (end-over-end, axial, oscillatory)

6.1.6.2 Reel diameter (number of container positions) and rotational speed

6.1.6.3 Can position study data for batch rotary retorts

6.1.6.4 Heating medium (steam, steam/air, water immersion, water spray) and
flow rate

6.1.6.5 Circulation method for water or overpressure media

6.1.6.6 Temperature distribution records

6.1.6.7 Retort venting schedule

6.1.6.8 Retort identification number

6.1.7 Loading of Retort

6.1.7.1 Loading or racking system details

6.1.7.2 Location of test containers in retort (slowest heating zone)

6.1.7.3 Container orientation

6.1.7.4 Location of thermocouples for retort temperature

6.1.7.5 Use of ballast containers to ensure fully loaded retort (some retort
systems)

6.1.7.6 Selected time interval for data logging system

6.1.8 Additional Information

6.1.8.1 Date

6.1.8.2 Test identification

6.1.8.3 Processor and location

file:///C|/iftps/protocols/hp_protocol.htm (12 of 15)6/5/2004 8:27:21 AM

HP_protocol

6.1.8.4 Individual(s) performing heat penetration test

6.2 Test-Phase Documentation:

6.2.1 Test run identification

6.2.2 Initial temperature of product at the start of heating

6.2.3 Time heating starts

6.2.4 Time vent closed and temperature, if applicable

6.2 5 Temperature indicated on MIG thermometer

6.2.6 Time retort reaches set point temperature (tc)

6.2.7 Pressure from a calibrated pressure gauge or transducer

6.2.8 Time process begins

6.2.9 Time cooling begins (pressure cooling, if applicable)

6.2.10 Time cooling ends

6.2.11 Rotation speed (if applicable)

6.2.12 Cooling water temperature

6.2.13 Any process irregularities or inconsistencies

6.3 Post-Test documentation:

6.3.1 Container net and gross weight check for leakage

6.3.2 Thickness of container

6.3.3 Location of the thermocouple and whether or not it is impaled in a food

particle

6.3.4 Measurement of container vacuum (rigid metal and glass) or residual air

file:///C|/iftps/protocols/hp_protocol.htm (13 of 15)6/5/2004 8:27:21 AM

 HP_protocol

content (flexible and semi-rigid containers)

6.3.5 Post-processing product characteristics: syrup strength, appearance,

viscosity, headspace, drained weight, pH, consistency, shrinkage, matting,
clumping

6.3.6 Container location and orientation (jumble pack)

7. LITERATURE CITED

ASTM. 1988. Standard Guide for Use in the Establishment of Thermal Processes for Foods
Packaged in Flexible Containers. F 1168-88. American Society for Testing and Materials,
Philadelphia, PA.

Bee, G.R. and Park, D.K. 1978. Heat penetration measurement for thermal process design. Food
Technol. 32(6): 56-58.

CFPRA. 1977. Guidelines for the Establishment of Scheduled Heat Processes for Low-Acid Foods.
Technical Manual No. 3. Campden Food Preservation Research Association, Chipping Campden,
Gloucestershire, UK.

Ecklund, O.F. 1956. Correction factors for heat penetration thermocouples. Food Technol. 10(1): 43-
44.

IFTPS. 1992. Temperature Distribution Protocol for Processing in Steam Still Retorts, Excluding
Crateless Retorts. Institute for Thermal Processing Specialists, Fairfax, VA.

NFPA. 1985. Guidelines for Thermal Process Development for Foods Packaged in Flexible
Containers. National Food Processors Association, Washington, DC.

Pflug, I.J. 1975. Procedures for Carrying Out a Heat Penetration Test and Analysis of the Resulting
Data. University of Minnesota, Minneapolis, MN.

• Prepared by The Committee on Heat Penetration Institute For Thermal Processing

Specialists Approved for Publication Nov. 10, 1995

• The Institute for Thermal Processing Specialists is a non-profit organization established

exclusively for the purpose of fostering education and training for those persons interested in
procedures, techniques and regulatory requirements for thermal processing of all types of food or
other materials, and for the communication of information among its members and other
organizations.

file:///C|/iftps/protocols/hp_protocol.htm (14 of 15)6/5/2004 8:27:21 AM

HP_protocol

• Part of the mandate of the IFTPS Committees is to develop protocols to be used as guides for
carrying out the work of thermal processing specialists. This is the first such protocol prepared by
the Committee on Temperature Distribution and reviewed extensively by members of the Institute.
The protocol has been approved by the Board of Directors. This document may be photocopied
in its entirety for use.

• Single copies of the protocol, as well as information on membership in IFTPS may be obtained
from: Institute for Thermal Processing Specialists, 304 Stone Rd. W. Ste. 301, Guelph, ON N1G
4W4 Phone: (519) 824 6774 Fax: (519) 824 6642, E-Mail: info@iftps.org

file:///C|/iftps/protocols/hp_protocol.htm (15 of 15)6/5/2004 8:27:21 AM

 OPERATIONS IN THE THERMAL PROCESSING
AREA

OPERATING PROCESSES
9 CFR 431.5(a) requires that a LACF manufacturer post the operating processes and
venting procedures to be used for each product and container size being packed in a
conspicuous place near the processing equipment, or place the processes where they
are readily available to the retort operator and to the Consumer Safety Inspector (CSI).
During the CSI’s verification checks, it must remember that the firm’s operating
process may be different than the firms scheduled process for the same product. Many
firms employ an operating process of one to two degrees above their filed scheduled
process temperature and one to two minutes longer then the filed process time to
compensate for minor fluctuations in the steam supply and possible improper
employee setting or reading of timing devices. This process is called the firm's
operating process. If the operating process exceeds the scheduled process, a drop of
time or temperature below the operating process is not a process deviation if the drop
is not below the scheduled process. The firms scheduled process should be used to
evaluate the thermal process for that product.

INITIAL TEMPERATURE
Initial temperature (I.T.) is defined in 431.5(c) as the average temperature of the
contents of the coldest container to be processed at the time the thermal processing
cycle begins, as determined after thorough stirring or shaking of the filled and sealed
container.
The initial temperature of the contents of one container to be processed must be
determined with sufficient frequency to ensure that the temperature of the product is no
lower than the minimum initial temperature specified in the filed scheduled process.
The regulations do not require that the initial temperature of each retort load of product
be checked. The closer that a firm operates to the minimum initial temperature in the
filed scheduled process the more critical measurement of the initial temperature at
frequent intervals becomes.
When initial temperature is measured in those products which incorporate frozen
ingredients extra care may need to be taken to insure that the temperature reading is of
the (average) temperature of the contents of the container and not just the temperature
of the covering liquid. Initial temperature may have a significant effect on the thermal
process delivered to the product, and the effect may be determined only through the
analysis of process establishment data for that product.
Initial temperature is normally determined using a dial, electronic or other type of hand
held thermometer. Glass stem thermometers are normally not used to determine initial
temperature because of the potential risk of breakage. Firms have attempted to use
pyrometers to measure initial temperature with mixed results. The use of pyrometer's
to measure the outside temperature of a container to determine the initial temperature
of a process requires adequate studies by the firm to document a correlation between
outside container temperature and the actual product initial temperature in the
container.

When determining the initial temperature of containers being processed by steam, a

container is normally selected from one of the first containers going into the bottom
layer of the first retort crate. This container is then set aside where it is not subject to
extreme changes in temperature. At the time that the retort lid is closed and the steam is
turned on the initial temperature in the container is determined. This same procedure is
normally acceptable for all batch type retort systems except as noted. For those retort
systems using water to cushion the fall of containers into the retort, or where water is in
the retort prior to the addition of the containers, provisions must be made to insure that
the temperature of the water does not lower the initial temperature of the containers. In
those instances where water comes in contact with the containers prior to beginning the
thermal process, the initial temperature of the process may be either the temperature of
the contents of the container or the temperature of the water in the retort, whichever is
the lowest. In systems that use cushion water, such as the crateless retort system, the
initial temperature may be the temperature of one of the last containers to enter the
retort, if the cushion water is maintained at a high temperature. For continuous retort
systems a container should be obtained just prior to entry into the retort system for
initial temperature determination.

Line breakdowns and processing delays may cause the initial temperature in containers
to fall below the minimum scheduled initial temperature. During inspections of LACF
manufacturers the investigator should determine the firm’s procedures for handling
product in the event of thermal processing delays. When a product is placed into a retort
that has to be cooled to restart the process, or to move the product to a second retort for
processing, a new initial temperature may have to be determined.

CRITICAL FACTORS-MEASUREMENT EQUIPMENT

A variety of equipment is used to measure critical factors including: scales,

thermometers, gauges, and consistency-meters or devices. The accuracy of the
equipment must be documented by the LACF manufacturer. There is no specific
requirement in the LACF regulations that equipment used for the measurement of
critical factors be checked for accuracy and calibrated as necessary. Good
judgment however dictates that equipment used to measure critical factors be
accurate. The investigator can determine the accuracy of scales, thermometers and
gauges used to determine critical factors by making comparison measurements
during the factory inspection. It is suggested that the manufacturing firm also
make accuracy checks on their scales and thermometers on a routine basis and that
records of these checks be made. If a thermometer used to determine initial
temperature or a scale used to determine fill weight is found to be out of
calibration, the thermal process for the product for which the device was used may
be in question back to the date that the measuring device was last checked for
accuracy.
TIMING DEVICES
Devices used to time retort thermal processes must be accurate. Pocket and wrist
watches are not considered satisfactory for timing purposes. Even though wrist and
pocket watches may be accurate, one problem noted with the use of wrist watches is
that several people involved in separate portions of the thermal process may use wrist
or pocket watches with different times of the day. When this happens the thermal
processing records do not correspond to each other. A large wall clock which can be
read from all areas of the thermal processing room is the best method for timing
thermal processes. If more than one clock is used in the thermal processing area they
both should be set to the same time of day. During the inspection of LACF
manufacturers the accuracy of the timing clock should be checked with an accurate
stop watch.
431.5(d) states digital clocks may be used if the operating process and the venting
schedule have a 1 minute or greater safety factor over the scheduled process and venting
schedule. If the digital clock reads out to the second this requirement is not necessary.
When timing clocks are read, the method used must be conservative to insure that the
time of vent, come up time, the time of thermal processing, and other operations are
carried out for the required time interval. Except in those instances where automatic
equipment is used to record times, the operator normally records operations in the
thermal processing area in full minutes (e.g., 7:15). If time is not recorded to the
second that the operation takes place then the operator must record the time for the
beginning of the operation at the next full minute and the time for the end of the
operation to the last full minute to insure that the full required time for an operation is
achieved (e.g., if the retort vent is turned on at 07:10:15, the operator would record
07:11 and if the retort vent was turned off at 07:10:15, the operator would enter 07:10).
Operations in the retort room must be monitored during the inspection to insure that
timing of the operations are accurate. Use of a stop watch by the investigator insures
that accurate time intervals are measured.
CONTROL OF RETORT TRAFFIC
431.5(b) defines that traffic in the retort room and processing area must be controlled to
prevent unprocessed LACF from circumventing the thermal process. The retort area
should be designed so that product enters one end of the processing area and leaves the
opposite end. This can be done in several ways depending upon the retort system in use.
For batch retort systems a routine procedure should be designed by the firm to stage
unprocessed product in an area separate from processed product. When multiple vertical
retorts are arranged in rows or rings, the product should enter the row or ring at a
different location than product exits the ring or row. In systems using continuous
conveyors or chains to move the product through the retort system the entry and exit of
product should be physically separated if possible to prevent the mixing of processed
and unprocessed containers. Containers which are found to be on the floor or off of
normal conveying equipment should be destroyed.

Crates and containers of LACF products must be identified in a manner which will
readily identify the status of the product. One method of identifying the status of LACF
product containers is through the use of thermal indicators. Thermal indicators are
placed on the containers, on one container in a retort crate, or on the retort crate itself.
Thermal indicators may be impregnated onto a paper tag to be attached to a retort crate,
painted onto the surface of a container or crate, incorporated into a tape to be placed
onto a container or crate, or incorporated into an ink jet spray which is applied by the
can manufacturer or canning firm. Some container manufacturing firms incorporate
thermal ink into a container manufacturing code which is placed on each container.
Thermal indicators can be purchased to meet the temperature range of the thermal
process being used. Thermal indicators do not however indicate that an adequate
thermal process has been applied to the LACF product, only that the product has been
subjected to a heat source. The thermal indicators should be examined following
processing and written records of changes in thermal indicators should be made. In lieu
of thermal indicators the firm can use other effective means of visually distinguishing
between processed and unprocessed containers.

STEAM SUPPLY
Although other methods of heating LACF are being developed, steam is the
predominant heating medium used to process LACFs. The steam may be used to
directly or indirectly heat the products or containers. Steam in modern canneries is
normally produced in remote steam boilers. Two common types of steam boilers or
generators found in canneries are the fire-tube and water-tube. Smaller boilers of the
"packaged" boiler type are almost always fire-tube boilers, and in physical appearance
are unusually long and relatively low. Such boilers are often referred to as "scotch-
marine" or "marine" type boilers. Larger boilers which have been constructed in place
are almost always water-tube boilers, and are usually nearly square and quite high,
some times 4 or 5 stories high. The fire-tube boiler is operated at pressures normally
under 150 psi. One advantage of the fire-tube boiler is the large water storage capacity.
Because of this feature, wide and sudden changes in steam demand are met with little
change in pressure. Watertube units on the other hand are capable of considerably higher
overloads. Boilers may be fired using a variety of fuels including, natural gas, liquid
propane gas, fuel oil, coal and wood. The method of firing the boiler may have an
impact on the steam pressure supply and recovery time.
Boiler or steam generator capacities are normally listed in terms of horsepower or lbs of
steam per hour. The term horsepower is defined as the ability of the unit to change
approximately 34 lbs of water at 212° F to 34 lbs of steam at 212° F. If boiler capacity
is given in pounds of steam per hour it can be converted to equivalent number of horse
power by dividing by 34.5. The rated capacity of a boiler is not an absolute measure of
the amount of steam that can be generated. Fire tube boilers may be operated at 135 to
150% of the rated capacity and water tube boilers may be operated at 150 to 200% of
capacity. Operation of the boiler depends upon proper maintenance of the boiler. A
boiler with heavily encrusted scale in the tubes or one which is not properly fired may
not be able to even meet the rated capacity of the boiler. This is usually beyond the
ability of the investigator to determine.

Steam pressures in the main steam line (header) may vary depending upon the
operation of the boiler(s) and the demand upon the steam supply. Boilers are normally
operated by either of two methods, use of modulating burners, or on-off operation of
the boiler. Modulating control is normally used in larger installations. Small plants
usually operate by on-off operation of one boiler; if additional boilers are used they are
normally fired at a fixed rate. The pressure gauge on the main steam line should be
watched over a period of time to determine if there are large fluctuations in steam
pressure. Modulated systems will normally have only small variations in the steam
supply; however the variation in on-off systems can be quite large. A reserve steam
capacity is sometimes obtained by operating the boilers at a high pressure (150 psi) and
using a reducing valve to reduce the steam pressure to (100 psi) at the retort steam
supply header.

Steam header pressure at the retorts of 100 to 125 psi is recommended for best
performance. Lower steam pressures can provide for adequate operation of retort
systems if the steam supply valve and plumbing of the retorts is carefully selected.
Temperature distribution testing in the retort system should be performed on these
systems to document adequate operation under the highest plant steam demand. The
greatest steam demand for retort systems normally occurs when the maximum number
of steam retorts are being vented or during the heating or come-up period of other retort
systems. A standard three or four crate vertical still steam retort can require from 2,500
to 6000 lbs of steam per hour (depending upon the size of the steam inlet) during
venting. One-fourth to one-half of the total steam demand of the retort is required for
venting. The steam demand of the retort rapidly drops to 100 to 150 lbs per hour after
the vent is closed and the retort reaches processing temperature. Other retort systems
have similar peak demands during the initial heating phases of the retort and product.
The steam supply to the retorts must take into consideration the maximum number of
retorts to be vented or brought to processing temperature at one time and any other
equipment, such as blanchers, steam kettles, steam peelers, and steam exhaust boxes,
which may have a steam demand at the same time. The steam demand of the entire
plant should be taken into consideration during the establishment of venting and come-
up schedules for retort systems. Fluctuations in the header steam pressure should be
correlated with fluctuations in retort temperatures, long vent periods and long come-up
times in the retort systems.

Most boiler systems require the addition of water treatment chemicals to prevent the
buildup of scale on the boiler tubes and to prevent corrosion in the boiler system. When
the steam comes into contact with the LACF, through direct injection of the steam into
the food; during the exhausting of containers in a steam exhaust box; through injection
of steam into the headspace of containers to form a vacuum, or through any other
means, the boiler additives must be approved for use as a food additive and labeled for
that use as per 21 CFR Part 173.310, Boiler Water Additives.

THERMAL PROCESSING SYSTEMS INSTALLATION AND

INSTRUMENTATION

Although retort systems vary from still batch type retorts to more complex continuous
retorts, employ different heating mediums during processing, and may use control
systems ranging from operator to computer controls; there are still basic equipment
requirements specified in the LACF regulations 431.6 that are applicable to all retort
systems.

MERCURY-IN-GLASS (MIG) THERMOMETER

Each retort system used for the thermal processing of LACF(s) must be equipped with
a MIG thermometer as per 431.6(a)(1)(i). This is emphasized in the LACF regulations
by being repeated for each specific retort system covered
431.6(a)(1)(ii) allows other temperature-indicating devices, such as resistance
temperature detectors, used in lieu of mercury-in-glass thermometers, provided they
meet know, accurate standards for such devices when tested for accuracy.

The MIG thermometer is the reference instrument for all temperature readings,
including vent temperatures, come-up temperatures and process temperature during the
processing of LACF(s).

The regulations require that the MIG thermometer be graduated in divisions which are
easily readable to 1° F (1/2° C) and whose temperature range does not exceed 17° F (8°
C) per inch (2.54 cm). The thermometer may be graduated in 2° F (1° C) divisions as it
is possible to read a MIG thermometer graduated in this manner to the nearest 1° F
(1/2° C). The LACF regulations require that MIG thermometers be tested for accuracy
upon installation, and at least once per year after that. It is important that the MIG
thermometer be tested/calibrated at the operating temperature of the retort system (i.e.
240° F, 250° F, 260° F etc.) and if possible in the heating medium used in the retort. If
the retort is operated at more than one processing temperature or over a wide range of
temperatures the MIG thermometer should be checked at all of the temperatures
normally used for processing LACF(s). The MIG thermometers should be tested
against a thermometer that can be traced back to an NIST (National Institute of
Standards and Technology) Standard thermometer. The standard thermometer should
also be checked for accuracy on a routine basis. Documentation should be available for
the calibration of the standard thermometer used and its last check for accuracy. The
accuracy of the standard thermometer should be checked at least once every 3 years
depending upon how it is handled and stored.

One way that firms using steam for thermal processing can check their MIG
thermometers is to use a cross made of 3/4 inch pipe for holding the thermometers with
1/16 inch holes drilled in the fittings to provide for a flow of steam past the
thermometer bulb. The cross is then mounted on a retort or steam manifold with a
certified standard thermometer in the center and one MIG retort thermometer to be
tested in each of the two outside arms. The thermometers are then allowed to heat to
equilibrium for 10 to 15 minutes. If an adjustment is needed the face plate screws are
loosened and the face plate is adjusted on the MIG thermometers. After the adjustment
another reading is taken to insure that the thermometer is now reading the same as the
standard MIG thermometer.

The installation of the standard thermometer in the retort next to the MIG thermometer
to be checked and the use of a circulating laboratory oil bath are also acceptable
methods used to check MIG thermometers for accuracy.

Records should be kept of the accuracy check of all MIG thermometers which include
the date of the last check, the person performing the check, the standard used, the
method used, and the amount of correction needed to bring the thermometer back into
calibration. The regulations recommend that each thermometer be identified with a tag,
seal or through some other means that identifies the date on which the last accuracy test
was made. The MIG thermometer must at least be identified in a manner that will allow
the thermometer to be matched with the thermometer calibration records.

MIG thermometers that have a divided column, that are broken, or which can not be
adjusted must be repaired or replaced immediately.

The MIG thermometer must be installed in a manner that it can be easily read, without
the operator having to go to extraordinary measures, such as entering a steam flow,
touching hot equipment, or climbing a ladder to make the reading. If it is difficult for
the MIG thermometer to be read, the operator will be more likely to use the recording
chart or some other method to obtain temperature readings, not the MIG as required by
the regulations.

TEMPERATURE RECORDING DEVICE

The LACF regulations in 413.6(a)(2) require that each retort system be equipped
with an accurate temperature-recording device. This has been interpreted to mean that
the recording device provides a continuous record of the temperature in the retort
system during thermal processing. Common systems found use circular or strip charts
which are marked with ink pens, electrical sparks, pressure pins, or which are created
by graph plotters at the time temperature readings are received.

The regulations require that graduations on the temperature-recording device charts

must not exceed 2° F (1° C) within a range of 10° F (5.5° C) of the processing
temperature. A working scale of not more than 55° F per inch (12° C per Cm) is
required within 20° F (10° C) of the processing temperature. A ruler can be used during
the inspection to determine the firm’s compliance with this part of the LACF
regulations. The object of the chart specifications is to provide a chart which can be
easily read by the operator and record reviewer. The regulations require that the
temperature recording chart be adjusted as closely as possible to the reference MIG
thermometer but to be in no event, higher than the known accurate reference
thermometer. The working accuracy of most recording devices is at least 1 F (1-1/2ºC).
In most instances the recording chart can be adjusted to agree with the MIG
thermometer to within 1 F (1-1/2ºC).

The temperature recorder should provide a fine temperature recording line which can be
easily read to the nearest 1 F (1/2C). A conservative approach should always be taken

when reading a wide line on a temperature recording curve or line. The temperature
recorded should always be determined by reading the bottom of the recorded line on the
temperature chart.

The pen arm on a circular chart recorder should follow the time curve on the chart.
Failure of the pen arm to follow the time curve indicates that the pen is out of
adjustment, bent, or that the wrong chart is being used. It is evident that the pen is not
following the temperate curve on the circular chart when it is noted that the temperature
curve travels back in time as the pen arm moves up or down on the chart. Some of the
more common recorders found in use have a mark inside of the chart case for adjusting
the arc of the pen. The number of the chart to use with the recorder may also be
stamped inside of the recorder case.

Recorders are driven either by electrical or mechanical wind-up clock mechanisms. If

driven by a wind up clock the firm must insure that the clocks are wound on a daily
basis. The recorder chart should be adjusted at the beginning of the production day to
agree with the time of day. The majority of charts in use can be adjusted to agree at
least to within 15 minutes of the time of day. The accuracy of the timing mechanism
should be determined over a designated time interval through the use of stop watch. If
the timing mechanism is not accurate, the recorder will not provide accurate
temperature recordings of the thermal process.

A means of preventing unauthorized changes to the temperature recorder must be

provided by the firm. This can consist of a locked recorder box, and/or a posted notice
from management that only authorized persons are allowed to make changes.

The temperature recorder probe must be installed in the retort in a manner which will
provide a true recording of the retort temperature. The recorder sensing probe is
normally installed next to or in the same manner as the MIG thermometer. The recorder
is then adjusted to the MIG thermometer.

The LACF regulations recommend that each retort system be equipped with a pressure
gauge that is graduated in divisions of 2 lbs or less. A pressure gauge is necessary for
observing the pressure during pressure cooling, and processing over-pressure in those
systems using air or steam to create pressures higher than those created by the system
temperature. The pressure gauge is also an extra safety device which lets the operator
know if excess retort pressure is being created.

Vents are large pipes, located opposite the steam entry on steam retorts, used to expel
the air from the retort prior to beginning the thermal process. Retort systems other than
steam retorts sometimes identify a purge valve, used for removing air from the system
to allow for the addition of water to a processing drum or for the rapid introduction of
steam to a steam-air retort, as a vent valve. The valves on these systems do not serve
the same function as the vent valve on a steam retort. The operation of the vent or purge
valve may be critical to the thermal process achieved in the retort system. Bleeders are
small openings required on steam retorts to remove air from the retort during
processing, promote circulation, and remove condensate from specific retort systems. A
bleeder is also necessary to ensure adequate steam flow past thermometer bulbs. They
should be open at all times during venting, come-up and thermal processing. Bleeders
must be installed in a manner that allows the operator to observe that they are
functioning during operation of the retort.

Mufflers are mechanical devices placed on bleeders or vents of steam retorts to reduce
the noise of the escaping steam. If mufflers are used the LACF manufacturing firm
must have information on hand in the form of temperature distribution data or other
documentation, such as a letter from the manufacturer, that shows that the mufflers do
not impede the flow of steam.

STEAM CONTROLLERS

Automatic steam controllers are required by the LACF regulations 431.6(a)(3) for all
retort systems. The automatic steam controller may operate independently of or in
conjunction with the temperature recorder. Steam controllers are of two main types:
on/off or modulating. With an on/off system the steam valve is either fully open or fully
closed. In a system with an on/off steam valve you would expect to find fluctuations in
the temperature curve produced by the temperature recorder. Modulating systems control
the steam valve to proportionally supply steam to the system as needed.

One method of retort temperature control found prior to the current LACF regulations
in some U.S. LACF plants, and still found in LACF plants in foreign countries, is the
operator manually controlled steam valve. In these retort systems the operator observes
the steam pressure on a retort pressure gauge and/or the retort temperature on a MIG
thermometer, or on some other type of thermometer. The steam valve is then opened
and closed by the retort operator to maintain the required steam pressure or
thermometer readings. In some plants where this type of control has been used, it has
been noted that by assigning one operator to each retort, the steam supply to the retort
can be controlled to provide for a consistent temperature. The retort temperature control
is dependent upon the operator observing the retort steam pressure and/or temperature
constantly. This type of steam/temperature control does not meet the requirements of
this section of the regulation.

The temperature of saturated steam of high quality bears a fixed relationship to its
absolute pressure (psia). In most instance steam is measured as gauge pressure (psig),
which has its zero point at 14.7 psia (equivalent to atmospheric pressure at sea level).
15.1 psig (Pounds per Square Inch Gauge Pressure) of steam at sea level is equal to
250F. Attachment 1 is a table which provides the corresponding gauge pressure and
process temperatures at various altitudes. Gauge pressures above those listed for the
corresponding temperatures may indicate air pockets in a steam retort system.
One of the oldest methods of temperature control in steam retort systems is the use of
the relationship between steam pressure and temperature in the retort. In this type of
control system a pressure line is connected between the retort and a steam control
valve. The diaphragm on the control valve is opposed by a spring which pushes against
the valve stem and opens the valve. When the steam is turned on to the retort the steam
pressure in the retort is low and the steam control valve is forced open by the spring
tension. As the pressure/temperature in the retort rises, steam pressure against the
diaphragm forces the steam valve to close, and less steam is supplied to the retort. As
the pressure/temperature in the retort fluctuates the valves opens and closes to modulate
the steam supply to the retort. This type of controller may provide for adequate
temperature control if it is well maintained. You will normally see fluctuations in the
temperature recorder curve as the pressures changes in the retort and steam supply.
Firms using this type of controller normally operate several degrees above their filed
scheduled process temperature to account for fluctuations in the temperature in the
retort.

Control of steam supplies to retorts has been reported using valves which are connected
to the steam header. One type of valve is actuated in one direction by a lever arm with
adjustable weights, operating against an opposing fixed spring. In another type the
valve is set to open a fixed amount by adjusting the compression of a moveable spring,
operating against an opposed fixed spring. If the steam header pressure does not
fluctuate appreciably, these will perform satisfactorily. If the header pressure does vary,
the retort pressure/temperature will vary also; for these valves are essentially steam
pressure ratio valves.

For example: Assume that the header pressure is 105 psig when a valve of this type is
adjusted to hold 15 psig (250 F) in the retort. If the header pressure drops to 90 psig at
any time, the retort pressure will drop to 12.5 psig (245 F).

(P1-P2)/P2 = pressure ratio therefore (105-15)/15 = 6

and (90-15)/X = 6, or X = (90-15)/6 = 12.5 psig

For this reason in those systems which use these types of controllers it is important to
observe the retorts operate through several cycles to determine if temperature
fluctuations are being caused by fluctuations in the steam supply. Using this type of
steam controller to supply steam to more than one retort would not meet the
requirements of 431.7(a)(3). Fluctuations in temperature control should be documented
during the inspection. Records should be reviewed to determine if process deviations
have occurred because of fluctuations in steam supply to the retorts.

Self-actuated steam supply/temperature control valves which operate directly off of the
pressure generated in a liquid/vapor filled temperature sensing tube are available for
temperature control in industrial situations. In this type of control system the vapor
generated by the heating of the liquid in the temperature sensing bulb is used to exert
pressure on the diaphragm of the steam control valve. The pressure on the diaphragm is
opposed by a spring. As the liquid heats up in the sensing tube the gas pushes on the
valve diaphragm causing the valve to close. As the temperature drops the spring forces
the valve open. Different liquids are used to fill the sensing tube depending on the
temperature range to be controlled. The system temperature would be adjusted by
adjusting the spring tension on the steam control valve. This type of temperature
control is not normally found on retort systems.

One of the most common types of retort temperature control systems found in the U.S.
is the pneumatic (air to open) steam control valve (Attachment 2). This valve is opened
by supplying air to a diaphragm which is connected to the valve stem. The valve is
closed by spring pressure on the valve stem. The valves are air-to-open for safety
reasons. If the power or air supply fails, the loss of air to the system results in the steam
valve closing and the retort pressure/temperature falling. These valves are commonly
connected to a mechanical recorder/controller which controls the supply of air to the
valve (Attachment 2) when using the mechanical recorder/controller a temperature bulb
in the retort is connected through a thermal tube to a Bourdon tube located in the
control panel. The temperature changes in the retort cause the Bourdon tube to expand
and contract.

Expansion/contraction of the Bourdon tube causes the recording arm to move which
also controls the amount of air to the control valve. As the temperature in the retort
rises, the supply of air to the valve diaphragm would be reduced, the spring would force
the valve partly closed and less steam would be supplied to the retort. As the
temperature in the retort starts to fall, more air is supplied to the valve diaphragm and
the valve is forced open, with more steam being supplied to the retort.

Pneumatic air controlled valves are also common in many advanced computer
controlled retort systems. In these systems the air supply to the steam control valve is
usually controlled through an electronic solenoid.

With any retort using air for control of the system it is very important that the air supply
to the instruments and control valves be kept clean and free of oil, water, rust and other
contaminants. It is ideal for the air supply to the instruments to be separate from the air
supply to the rest of the plant. This air supply should be equipped with devices for
keeping the air clean, such as air filters, condensate traps, water drains and oil traps.
Maintenance of the air supply system on a routine basis is essential to the continued
accurate operation of pneumatic air controls.

A simple mechanical/electrical control system for an electronic solenoid operated steam

control valve may consist of a temperature dial to set the selected retort temperature, a
temperature sensing element in the retort which is connected to a Bourdon tube or some
other type of expanding gas or liquid sensor, and a steam supply valve which is
controlled by air, an electric solenoid or rotary motor. These systems act much the same
way that a thermostat in your house would be used to control the temperature. As the
set temperature in the retort is reached the expansion of the liquid/gases in the
temperature sensing element causes the Bourdon tube to expand, expansion of the tube
causes electrical contacts to open or close, depending upon the design of the control
mechanism. As the electrical contacts close an electrical source is supplied to an
electronic solenoid or motor to operate the valve. This type of system may supply steam
in an on/off fashion instead of proportionally.

A similar type system would replace the Bourdon Tube with a solid state electronic
temperature controller using a thermocouple or resistance temperature devices (RTD) to
sense the temperature in the retort. The solid state electronic circuits would then be set
to control the retort at the selected operating temperature through the use of an
electronic solenoid, solenoid/air or electric motor operated steam control valve. The
solid state circuits may provide for on/off or proportional operation of the steam valve
depending upon the control system and manufacturer.

In systems using RTDs or thermocouples a low level electrical signal is sent to a

control mechanism. It is important not only for a firm to properly calibrate the
RTD/thermocouple but to insure that the electrical signal sent to the sensor is not
interfered with. The circuits (wires) used to transmit the signal to the signal convertor
or sensor must be designed and installed to prevent electrical interference on the circuit.
Electrical interference on the circuit can cause false readings to be received from the
RTD/thermocouple. The firm should have in place a system for routine calibration and
maintenance of RTD's and thermocouples including the complete control circuit.

MECHANICAL/ELECTRICAL TIMED RETORT CONTROL SYSTEMS

Addition of a manually set electrical/mechanical clock to the pneumatic air/electrically

controlled valve systems mentioned above provides for timing of the retort thermal
process. An additional mechanical/electrical clock for the timing of the vent cycle on
steam retorts further automates the system. These systems are designed so that both a
time and temperature must be reached for venting; the process timing does not start
before the process temperature is reached, and the process ends after the set process
time has been reached. These systems still require the observation and manual recording
of MIG thermometer readings and processing times.

In 1948 Taylor Instrument Co. supplied the LACF industry with the first fully
automatic controlled retort systems. Other manufacturers have introduced similar
systems since that time. These systems use electronic/mechanical clocks, stepping
switches electronic relays, pressure switches, solenoid valves and temperature sensors
to provide for automatic/pneumatic control of vent valves, bleeder valves, cooking
times, over-pressure, cooling water, cooling times, and draining of the retort. The
operators function is to set the process time, the thermal process temperature, and the
vent times to meet those of the operating thermal process. In order to start the process
the operator only has to push a start button. The control of the retort thermal process is
then through the controller. The system may be equipped with a series of lights which
indicate when the steam is turned on, when the process is up to temperature (start of
thermal process) and when the retort is in the cooling phase. The operator is still
required to observe and manually record MIG thermometer temperature readings,
processing times, vent times and other factors critical to the process. At the end of the
process the timing clocks are automatically reset to the preselected times. The system is
then ready for the next thermal process.

Because these systems are fully automatic, including the operation of the bleeder
valves, maintenance of the system is often neglected. Failure to adequately maintain the
system can result in failure of bleeder valves, vent valves and system controls to
operate properly. When these types of retort control systems are encountered the
investigator must observe the operation of the system through several cycles to insure

that all control valves are operating properly, that bleeder valves are fully open and
functional during the venting and thermal processing cycles, and that scheduled process
time and temperature parameters are being met.

Cam operated control systems have been used by U.S. and European equipment
manufacturers to automatically control retort processing including processing
temperature, pressure, processing times and cooling times. In these systems a cam is cut
out of plastic, metal or some other durable material. As the cam is turned by an
electrical/mechanical clock a cam follower rides upon the cam and operates a series of
electrical sensing switches. The electrical switches are used to operate electrical and/or
pneumatic control valves which supply steam and air to the retort or serve other
functions such as venting of the retort. Care has to be taken to cut the correct profile in
the cam to provide the correct thermal process. As the cam wears the profile may
change, changing the thermal process.

European manufactures such as LaGarde and Stock have used card readers to control
retort temperature, retort pressure and process timing. In these systems a card made of
plastic, metal or paper is either cut or punched to a certain profile for each thermal
process. The card is then placed in a card reader. In the LaGarde system the card is read
by a light source. As the card passes through the reader the light source activates limit
switches. In the Stock system the card comes into contact with the limit switches as is
passes through the card reader. The limit switches control the signals sent to the control
valves which may be either electronically or pneumatically controlled. The profile of
the cards are very important. Care has to be taken to punch or cut the correct profile for
each thermal process. If the profile is not cut correctly for the process the correct
process will not be provided. The cards also become worn or damaged during use and
care must be taken to maintain the cards in good working condition.

DIGITAL ELECTRONIC CONTROLLERS

In recent years digital electronic controllers have replaced the relays and sensing
switches of mechanical/electrical control systems. Digital control systems may range
from the single-loop controller to complex high-end computer systems.

If the process to be controlled consists of numerous sequential (logical) steps, the

controlling device can be a first-level computer device called a logic controller. The
logic controller may be set up as a single loop controller.

A single loop controller would be responsible for controlling one function such as
temperature in the retort. The controller loop would be programmed to control the retort
temperature within set temperature parameters. The loop would consist of the
microprocessor controller, a sensor, and actuator for the steam valve and a
digital/analog signal converter. The simple single loop controller contains Read Only
Memory (ROM) which is manufactured into the controller or programmed into the
controller by using Programmable Read Only Memory (PROM), Erasable
Programmable Read Only Memory (EPROM), or Electronically Erasable
Programmable Read Only Memory (EEPROM). PROM is field programmable by the
manufacturer or customer one time only by burning out fuses in the PROM
microprocessor chips. EPROM is electronically programmed by the manufacturer or
user. EPROM microprocessor chips can be reprogrammed by exposing the chip to an
ultraviolet light source which resets the original chip configuration. EEPROM
microprocessor chips can be reprogrammed by electronically erasing the memory on
the chip. ROM is normally used to control processes where the options of the customer
or operator do not need to be changed.

Random Access Memory (RAM) using battery backed volatile memory components is
another type of memory component. This memory requires a power supply but lends
itself to modification and reprogramming. Advanced microprocessor or computer
systems would normally use a combination of ROM and RAM to program control of
retort functions.

A more advanced system would use a programmable logic controller (PLC) which
would allow the operator or firm to alter the control limits of the controller. This type of
controller would use algorithms (a programmed procedure for solving a problem) to
control the loop. Algorithms are written to provide the microprocessor with a logical
sequence of events for solving a problem.

Control of multiple parameters such as temperature, pressure, rotation, etc may be

controlled by installation of several loop controllers controlled by one PLC,
microprocessor or computer.

With the advancement of technology, defining the differences between

microprocessors, minicomputers and mainframe computers has become more difficult.
Size is usually the distinguishing factor. The size of the computer needed for control
depends upon the number of loops to be controlled and whether the system is set up as
an independent (each retort control system is self standing), centralized (one computer
controls all retorts), or a distributed system (two or more computers talking to each
other).

In the independent system each retort would be controlled by its own PLC or
microprocessor. If one of the retort control systems failed the remainder of the systems
would continue to operate.
In a centralized system all data would be collected and analyzed by a central
computer. This provides for quick capture of all processing information and for control
from a central location. Failure of this control system would mean that all processing
systems would be down.

In the distributed system a PLC or microprocessor can be used for independent control
of each retort system. The retort microprocessor is then used to supply information to a
systems computer which captures all retort data for storage and printing. The systems
computer in turn is used to store process programs and to program the logic controls of
the microprocessor.

Computer controlled retort systems may be marketed with one or more peripherals
added to the basic PLC or microprocessor. Peripherals may include: keyboard or key
pads for programming and entering information, printers for printing stored and
captured in-process information, personnel computers for programming the PLC, CRT
(touch screens) for monitoring the process and entering information, and modems
which allow for connections to remote computers for programming or trouble shooting.

During inspections of LACF manufacturers using computers to control thermal

processes or to control other factors critical to the process the investigator must
determine the functions of the computer system.

In many cases LACF manufacturing firms will not have on hand detailed information
covering the development and validation of the software and microprocessors used on
their retort systems. Many firms buy the microprocessors as black boxes from the
equipment vendor. The investigator must then determine the functions of the control
system in as much detail as possible. It is important to remember that computer
controlled retort systems must function to provide for control of the thermal process,
the same as any other type of control system. The mercury-in-glass thermometer is still
the reference thermometer as per the LACF regulations. The operator is required to
read and record mercury-in-glass thermometer readings the same as for any other
control system (these may be entered into a computer record). Each retort system is still
required to be equipped with a temperature recorder as per the LACF regulations. This
recorder must provide a continuous record of the thermal process; must meet the
specifications of the LACF regulations; and must not record a temperature higher than
the MIG thermometer reading. It is important to determine that the system is
controlling the retort to meet the requirements of the firms filed scheduled processes for
time and temperature; that critical factors such as rpm's in agitating retorts and come up
time in water immersion retorts are being controlled; and that vent times and
temperatures for steam retorts are being adequately controlled. If the firm has a
schematic drawing of the control system this should be obtained or the investigator may
prepare a simplified schematic drawing, which will be helpful in explaining the system
operations. If the firm does not have detailed information on the microprocessor control
system the investigator should obtain any limited information that is available. At a
minimum this would include the vendor and model numbers of the computer control
system and the functions performed by the computer control system. Observation of the
system as it operates can be used to determine if critical factors such as RPM, vent
times, temperatures, pressures, and thermal process times are being adequately
controlled by the microprocessor. This may require observation of the system through
several thermal process cycles. The investigator should determine who is responsible for
programming the system, how the system is programmed, the name and number of
programmable functions, if the programming functions are password or otherwise
protected and who is responsible for record review and process verification.

It is also important to determine if the operator has the ability to override any of the
computer control functions. If operator override of computer functions are possible,
details on how this is done, what overrides are possible, and how this is reflected in the
thermal process record should be determined.

The investigator should determine how the system handles process deviations during
thermal processing. If the computer system is able to calculate new processes or chose
alternate pre-programmed processes the investigator must determine the parameters for
computing or selecting the alternate process.

During inspections where microprocessor or computers are being used to control thermal
processes in retorts the CSI should determine at a minimum:

1. The equipment specifications for software and hardware.

2. The critical factors that are controlled by the system.
3. How the critical factors are controlled.
4. How does the firm ensure that the microprocessor or computer is indicating the
correct information (validation).
5. How, and how often is the equipment calibrated and/or checked for accuracy.

The references "Guide to Inspection of Computerized Systems in Drug Processing"

Feb. 1983, U.S. Dept. of Health and Human Services, Food and Drug Administration
and "Software Development Activities" July, 1987, U.S. Department of Health and
Human Services, Food and Drug Administration, should be used as guides to inspecting
firms using complex computer controlled retort systems (these guides are currently
undergoing revision). DEIO also has in process 'Guide to Inspection of Computerized
Systems in the Food Processing Industry.

An example of a parameter that could be under digital electronic control is pressure in a

retort, which is normally controlled by adding or releasing air from the retort. A
common method for pressure control is the use of a pressure sensor to transmit a signal
to a pressure controller. The pressure controller will then send signals to position the air
supply and pressure release valves. Control of pressure through addition and release of
air allows for a more uniform pressure control in the retort. The valves used in pressure
control may be pneumatic, electric or a combination of these types. Control of other
factors critical to the proper operation of the retort system, such as water level in water
immersion retorts, water circulation in cascading & spray water systems, and RPM's in
agitating retorts may be monitored and controlled by a variety of methods, including
mechanical, electrical and combination systems.

It is important to remember that the system used must provide assurance that the retort
system is operating in a manner that the scheduled process will be delivered to the
LACF product.

RETORT VALVES

A variety of valve types may be used on retort systems including:

PLUG COCK VALVE - This valve consists of a tapered plug with a vertical slot which
fits into a tapered valve body. Full flow is obtained when the opening in the tapered
plug faces in the direction of flow. When the plug is rotated a quarter of a turn, flow is
stopped. Opening and closing the valve is usually accomplished by using a wrench or
lever applied to the valve stem. Plug cock valves are noted on retort bleeders and may
be used on retort vent lines.

GATE VALVE - Gate valves are full flow valves normally used to start or stop flow. A
gate (sliding shut-off wedge) within the valve body is raised and lowered through a set
of threads on the valve stem. The valve is operated by turning the valve stem counter
clockwise to open the valve and clockwise to close the valve. These valves are usually
either fully open or fully closed during service. When fully open the gas or fluid flows
through the valve in a straight line with very little resistance to flow. This feature
makes the valve ideal for use in the vent lines of steam retorts, where rapid removal of
air may be important to proper temperature distribution. A gate valve can normally be
recognized by a long stem, by the number of turns of the valve stem that it takes to
close the valve (more turns are needed for a gate as compared to a globe valve), and
sometimes by the appearance of the outside of the valve body (more square when
compared to a rounded globe valve). If the gate valve cannot be identified in this
manner the valve stem may have to be removed to identify the type of valve.

GLOBE VALVE - Globe valves are extensively used for the control of flow and where
positive shut off is required. A globe valve employs an internal seat within the valve
body. Hand operated globe valves are operated by turning the valve stem counter
clockwise to open the valve and clockwise to close the valve. Threads on the valve
stem cause the seal on the valve stem to mate with or move away from the valve seat.
Close control over flow is readily accomplished. As the fluid or gas moves through this
type of valve it must change direction. This results in increased resistance to flow. For
this reason this type of valve is not ideal for venting of steam retorts. Globe valves are
ideal for use on water and air lines where close control over flow is required. Globe
valves have a positive shut off feature which can prevent leakage of air and water into
retorts during processing.

BALL VALVE - Ball valves are quick opening, full flow valves, needing only a quarter
of a turn to be fully open. A ball with a non-restricting port rides in a valve body on
plastic non-sticking seats. Ball valves can provide a bubble tight seal. The ball valve
can be used for full flow (venting), and control (water and air supply) functions on
retorts.

BUTTERFLY VALVE - Butterfly valves are quick opening, full flow valves which
employ a metal disk which when rotated on a shaft seals against seats in the valve body.
Butterfly valves are normally used as throttling valves to control flow. Butterfly valves
may be found on some of the newer retort systems

DIAPHRAGM VALVE - Diaphragm valves contain a moveable diaphragm within the

valve body which fits against a valve body seat. When the diaphragm is raised or
lowered by the valve stem flow is increased or decreased through the valve. Diaphragm
valves may be found on some of the newer retort systems.

Valves may be operated by hand, pneumatically (by air, steam or other gas), electrically
(by a solenoid or motor) or by a combination of these methods.

Free flow valves such as the gate or ball valve are normally used on steam retort vent
lines. The use of globe or other type valves on steam retort vent lines is not prohibited
by the LACF regulations. If these types of valves are used, temperature distribution
studies are required to document adequate temperature distribution in the retort prior to
the start of the thermal process.

Valves which provide a tight seal, such as the globe or ball valve must be used on air
and water lines to prevent leakage into the retort during thermal processing. Valve seats
and seals must be maintained to prevent the valves from leaking. During a LACF
inspection the retort should be examined for evidence of leaking water and air valves.
Some firms may employ the use of double valves on air and water lines to insure that
no air or water is leaked into the retort during processing.

TEMPERATURE DISTRIBUTION

Temperature distribution is the work performed to ensure that the retort instrumentation
accurately reflects that adequate temperature distribution has been achieved throughout
the retort at the time that the sterilization cycle begins. This is accomplished by
distributing an adequate number of thermocouples or other temperature measuring
devices (TMDs) throughout the load (external to the containers), and making several
runs or tests to ensure that temperature differences have been minimized. The number
of thermocouples (TMDs) to be used is normally limited by the equipment available. A
minimum of 12 thermocouples has been suggested by The Institute for Thermal
Processing Specialists. With large retort systems and numerous retort crates a greater
number of thermocouples may allow for a more extensive test to be completed. At least
one thermocouple is placed next to the MIG thermometer and used as a reference
during the study. The worst case situation for temperature distribution normally occurs
when heat flow to the product is the greatest. The heat absorption rate of a convection
heating (heat currents are formed in the container) is much higher than a conduction
heating (heat must penetrate through the material) product. It is normally suggested that
a convection heating product in the smallest container processed or a special cold water
pack be used to test temperature distribution in still retorts. Other conditions may
present the worst case for temperature distribution in a specific retort system or for a
specific product or container type. This must be documented in the temperature
distribution study. In some retort systems temperature distribution tests must be
performed for each container type (e.g. glass, metal, plastic), for each container size, for
each container racking system, for each container shape, for each product produced and
for each individual retort system.

Acceptable temperature ranges in the retort at the time that the process begins varies
with retort systems and products. Normally you would expect to find all thermocouples
(TMDs) within 1ºF of the processing temperature at the time the process timing begins
for still steam retorts. For water immersion retorts you would normally expect to find
all thermocouples (TMDs) at or above the set point temperature and no greater than a
2ºF degree difference between the minimum and maximum TMD. Other conditions
may be acceptable to meet the requirements of adequate temperature distribution in a
particular retort system. These conditions should be documented in the temperature
distribution study. Equipment and procedures which fail to provide adequate
temperature distribution in a retort system prior to start of the process must be modified
to provide adequate temperature distribution.

There must be documentation on hand at the LACF plant, from the processing
authority, which specifies the come-up procedures (e.g. venting, cut-up time) to be
employed to ensure adequate temperature distribution is achieved at the time that the
thermal process or sterilization cycle begins. The firm must employ the same
procedures during production as were used to establish the temperature distribution in
the retort.

Among the factors which may affect temperature distribution are:

Initial temperature of the product

Loading configuration (retort crate and retort)
Retort geometry
Steam spreader design
Type of heating media (steam, water immersion, cascading water, water spray,
steam air etc.)
Circulation of heating medium
Use of agitation
Size, type and location of vent valve in steam retorts
Steam header pressure

In some foreign countries LACF manufacturers attempt to establish the effectiveness of

the retort by performing heat penetration tests in various areas of the retort, or by
performing numerous heat penetration tests using a limited number of containers placed
in different areas of the retort during several different process cycles. This method of
retort temperature validation has not been accepted by FSIS as being a valid method for
performing temperature distribution studies. Variations in such things as retort load,
retort cycles, product fill, and initial temperatures can cause temperature readings
obtained from thermocouples inside of the containers to vary by several degrees.

A good reference for temperature distribution protocol for steam still retorts has been
published by the Institute for Thermal Processing Specialists.

Heat penetration, in contrast to temperature distribution, is designed to measure the rate

of heating of the food product under consideration. In these tests thermocouples or
other temperature measuring devices are inserted into the containers to measure the
product heating rate. Not only should the slowest heating container in the test be
identified, but also the slowest heating zone within any given container. Thus it may be
necessary to do a preliminary "cold-spot" study to identify the slowest-heating zone
within the container prior to doing the actual heat penetration test on several containers.
In addition, the performance of heat penetration work must be based upon adequate
knowledge of the heat resistance of the microorganism(s) of concern in the specific
product to be processed. Finally, the heat penetration test must cover all the variables
expected to be encountered during the course of commercial operation in the plant.

Among the factors which may affect heat penetration results are:

Container position, geometry and heat transfer characteristics.

Type of heating medium
Product factors (e.g. fill weight, viscosity, particle size, percent solids, method
 of preparation)
Equipment factors (e.g. filling method, head space, rotational speed)

The information developed during the heat penetration test is then used along with
other information such as the heat resistance of the microorganism(s) in question (this
can be effected by the food being tested), and the numbers of microorganisms expected
to be present in the product, to calculate a theoretical process.

The theoretical process may be confirmed by using an inoculated pack. In an inoculated

pack a known amount of an organism with a known heat resistance is placed into each
container. The containers are then processed at various calculated process times and/or
temperature(s) and examined for surviving organisms. The objective of the inoculated
pack method is to determine the time/temperature combination that will kill all of the
spores added to the product. A similar method called the count reduction method uses a
procedure which relates the decrease in the numbers of spores from the initial number
to some final number with process Fº value. Processes may also be established using
other procedures such as chemical indicators to provide Fº values.

The process should be established by qualified persons having expert knowledge of the
thermal processing requirements of LACF, and having adequate equipment and
facilities to make such determinations. All critical factors, including the establishment
of venting or other come-up procedures to ensure adequate temperature distribution,
must be investigated by the processing authority. There must be some form of
documentation on hand at the factory; at least a letter or other similar transmittal from
the processing authority, which details all factors critical to the delivery of the
scheduled process.

Should no documentation exist at the plant, every effort should be made to determine
whether such documentation exists at any location, before leaving the plant.

Should the documentation for the scheduled thermal process be more extensive than a
letter or other similar document, a preliminary review should be made to determine if
any of the procedures are questionable (it may not always be possible to accomplish
this at foreign plants if the documentation is not in English).

The information from the processing authority should be compared with the operations
at the firm and with the information which the firm submitted with their scheduled
thermal process.

The LACF regulations require that crates, trays, gondolas etc. for holding containers
must be made of strap iron, adequately perforated sheet metal or other suitable material.
When perforated sheet metal is used for the bottoms, the perforations should be
approximately the equivalent of 1 inch holes on 2 inch centers. If divider plates are
used they should be perforated as above.

Other arrangements can be used as long as there is temperature distribution

documentation on hand for the equipment in use. It is important for good temperature
distribution to use a crate with as much open area as possible. The percent open area of
the crate bottom and the divider plate can be calculated by dividing the total open area
of the holes by the total area of the bottom or divider plate x 100. A divider plate which
meets the specification of the regulations (1 inch holes on 2 inch centers) has
approximately 27% open space. Tightly packed small round containers may cover over
90% of the divider plate. The holes in divider plates must be carefully designed to
provide for the maximum heating medium flow between the containers. By using
closely spaced smaller holes the percent open space can be dramatically increased. The
crates and divider plates in use should at least be no more restrictive than those used to
establish the retort operating procedures. When a firm changes the type or design of
divider plates the effect of the new divider plates must be evaluated by the firms
processing authority.

If dividers, racks, trays, or other means are used to position flexible containers in place
they must be designed and employed to ensure even circulation of the heating medium
around all containers.

Discuss equipment and procedures as they apply to each of the various types of retort
systems. In addition to the common types of retort systems discussed there are other
less common types which may be encountered.

When inspecting these systems always review the LACF regulations to determine
compliance of equipment installation and operation.
 RETORT SYSTEMS
FOR THERMAL PROCESSING OF LOW-ACID, CANNED FOOD
(LACF)

Equipment and procedures common to all retort systems has been previously discussed.
The following section will discuss equipment and procedures as they apply to each of the
various types of retort systems. In addition to the common types of retort systems
discussed, there are other less common types which may also be encountered.

Always review regulations 9 CFR 431.1-431.12 to determine requirements for equipment

installation and operations when inspecting these systems.

STILL STEAM RETORTS

Equipment and procedures for pressure processing in steam in still retorts are covered by
9 CFR 431.6(b)(1) of the LACF regulations.

Still steam retorts (Figures 1 and 6) are identified as vertical, in which the crates are
lowered by hand or overhead hoist into the retort; horizontal, in which the crates are
pushed or conveyed into the retort; or crateless (Figure 3), in which the containers drop
into cushion water in the retort. Vertical retorts vary from small one crate, to retorts
holding several crates. Vertical retorts are commonly found to be approximately 42
inches in diameter and to hold 3 or 4 crates of product. Horizontal retorts vary from small
one crate, to large retorts holding 12 or more crates of product. Retort size normally
depends upon the size of the firm, the amount of product to be processed at one time, the
length of the thermal process and the closing capacity of the firm.

Still steam retorts were one of the first types of retort systems used to pressure process
LACF. Steam under pressure provides a number of advantages for processing LACF
products in metal containers:

- It is an excellent medium for heat transfer

- Its temperature is easily regulated
- The steam pressure required in the retort in order to achieve the required
processing temperature serves to counter-balance the pressure built up inside of
the container during processing.
- Steam can be easily manufactured and held in reserve for immediate use.
- The stored energy property of steam makes it a superior heating medium as
compared to water or steam-air. The stored energy results from the fact that in the
manufacture of steam considerable heat (970 B.T.U.'s) is required to change one
pound of boiling water to one pound of steam at the same temperature. When the
steam condenses on the containers during processing this latent heat is given up to
the container. It is important in the operation of still steam retorts to remove air
from the retort prior to starting the process. Air in the retort acts as an insulator
around the containers which prevents steam from contacting the container. Air in

1
 the presence of high heat may also cause the containers to rust. Small amounts or
pockets of air in the retort can cause containers in those areas of the retort to be
under processed.

2
Air is removed from the retort prior to processing through the retort vent and bleeders. 9
CFR 431.6(b)(1) describes vent plumbing and operating procedures for various vertical
and horizontal still steam retorts. As long as the equipment is installed and operated
exactly as per the regulations, the vent times and temperatures given are adequate to meet
the requirements of the regulations for containers in jumble stack (containers randomly
dropped into the crates) or off-set stack arrangements.

The Grocery Manufacturers Association Bulletin 26L recommends venting schedules

similar to those found in the regulations. The recommendations found in Bulletin 26L do
not, however, apply to retort systems which utilize divider plates. Bulletin 26L suggests
that the venting schedules for still steam retorts using divider plates be obtained from a
process authority.

Each retort system must be equipped with a steam inlet large enough to provide sufficient
steam for proper operation of the retort. Steam may enter either the bottom or top portion
of the retort, but must enter that portion of the retort opposite the vent. This is important
to provide for adequate circulation of steam and removal of air during the venting of the

3
retort. It is recommended that the automatic steam control valve be of the same size or
larger than the steam inlet. This allows the use of the automatic steam controller during
retort venting. If an automatic steam controller valve of a size smaller than the steam inlet
line is used, a steam by-pass may be needed during venting and come-up to provide
enough steam to the retort to rapidly vent the retort. The steam by-pass may be manually
operated by the retort operator or automatically operated through the retort control
system. At the time that the retort reaches processing temperature the by-pass valve
would be closed. Control of retort temperature during processing would be through the
smaller automatic steam control valve. Use of a smaller automatic steam control valve
provides for more accurate control of processing temperature with less temperature
fluctuation.

Steam spreaders which are continuations of the steam inlet line inside of the retort should
not be larger than the steam inlet line. Steam spreaders are required in horizontal retorts.
In horizontal retorts, the steam spreader must extend the entire length of the retort. The
steam spreader should have perforations along the top 90º (that is within 45º on either
side of top dead center of the spreader). Horizontal retorts over 30 feet long should have
two steam inlets connecting to the steam spreader. In vertical still steam retorts, a steam
spreader is not required, however if one is used it should be operational. When used, the
spreader should be in the form of a cross with perforations along the center line of the
pipe facing the interior of the retort or along the sides of the pipe. The steam should not
flow directly onto the retort bottom (this erodes the metal) or directly onto the containers.

Vertical steam retorts are required to have crate supports to prevent the crate from sitting
upon the steam spreader.

The number of perforations in steam spreaders should be such that the total cross
sectional area of the perforations is equal to 1.5 to 2 times the cross sectional area of the
smallest restriction in the steam inlet. The following table can be used for guidance:

Number of Holes in Steam Spreaders of Steam Inlet Pipe Size

SIZE 1” 1-1/4” 1-1/2” 2” 2-1/2”

HOLES* PIPE PIPE PIPE PIPE PIPE
(INCHES)

3/16 47-62 81-108 111-148 183-244 260-346

1/4
27-36 45-60 62-84 102-137 147-196
3/8 2 1-28 28-37 45-60 66-88

1/2 11-15 15-20 26-36 36-48

*Inside Diameter

4
Vents must be installed in such a way that all air is removed from the retort before timing
of the process begins. Vents are normally controlled by a gate, plug cock or ball valve,
which must be fully open during venting. Vents must be installed so that a back pressure
is not created during venting. Vents must not be connected directly to a closed drain
system. Vent pipe(s) exits cannot be submerged under water during venting. On those
retort systems where more than one retort vent pipe from a single retort connects to a
manifold, the manifold must be of a size that the cross sectional area of the manifold is
greater than the cross sectional area of all of the connecting vents. The manifold may be
controlled by one free flowing valve. Where vents from more than one retort or manifold
pipes are connected to a header, the header must have a cross sectional area at least equal
to the cross sectional area of the connecting pipes from the maximum number of retorts
to be vented at one time. The header must not be controlled by a valve. Vent installations
may differ from the above specifications if the firm has evidence in the form of heat
distribution data that adequate venting of air is accomplished.

Bleeders are openings in retorts used to remove air entering the retort with the steam, and
to promote circulation of the steam in the retort. The LACF regulations require that all
retort bleeders, except thermometer well bleeders, have an inside diameter of no less than
1/8 inches when fully opened. Thermometer well bleeders are required to have an inside
diameter no less than 1/16 inch when fully opened. Bleeders must be wide open and emit
steam continuously during the entire process including the come-up time. The operator
must be able to observe the operation of the bleeders during processing. If the retort has
the steam entry in the top of the retort, a bleeder of adequate size must be installed in the
bottom of the retort to remove the condensate from the retort during processing. The
condensate bleeder has to be installed in a manner that allows the operator to observe its
function.

Vertical still retorts are required to have at least one bleeder opposite the steam entry.
Horizontal retorts are required to have at least one bleeder opening within one foot of the
outermost location of containers at each end of the retort, and at intervals of no less than
8 feet along the top of the retort.

As previously noted, each retort system must be equipped with a mercury-in-glass (MIG)
thermometer, a temperature-recording device, and an automatic steam controller. The
sensing bulbs for the MIG thermometer and the temperature recording device may be
installed within the retort shell or in an external well attached to the retort. External wells
or pipes must be connected to the retort through at least a 3/4 inch diameter opening, and
be equipped with at least a 1/16 inch diameter bleeder to provide for a free flow of steam
past the thermometer sensing bulb.

Air may be supplied to the still steam retort to provide overpressure during the water
cooling of containers in the retort. Considerable pressure is built up in the container
during thermal processing. To prevent buckling (the container ends become permanently
distorted) of the container overpressure from air or steam is provided during cooling. Air
overpressure is more easily controlled because the steam tends to collapse in the retort
headspace. The overpressure must be controlled within limits. Too great a pressure or

5
cooling for too long will panel (permanently distort the side panels) the containers. The
air supply line must be equipped with a tight fitting valve (e.g., globe or ball) to prevent
air leaking into the retort during thermal processing. Generally pressure cooling is needed
when processing container sizes with diameters above 401 (4 1/16 inches) at
temperatures greater than 240° F. Smaller containers processed at higher temperatures
may also require pressure cooling.

CRATELESS RETORTS

Equipment and procedures for crateless retorts, which are still steam retorts (see above),
are covered by 9 CFR 431.6(b)(1)(ix)(d) of the LACF regulations.

Crateless retort systems are manufactured by Malo Inc., by the FMC Corp. and by others.
Crateless retort systems are still steam retorts in which the containers are fed directly into
the retort from a continuous belt (Figure 3). Crateless systems are normally operated in a
series of from 2 to 6 or more retorts depending upon the firms requirements. One operator
can normally operate several crateless retorts at one time. Crateless retorts may be up to 8
feet high and 6 feet in diameter. The capacity of the retort is several times that of the
normal 3 crate vertical retort (over 10,000 cans for some smaller containers). Container
size is not limited by the retort design. Prior to filling the retort with containers, the retort
is filled to approximately half full with preheated cushion water at a temperature which
will not lower the product temperature below the minimum temperature specified in the
process schedule. When used, the automatic conveyor system is set to feed the preset
number of containers (depending upon can size) into the retort through the top sliding
door. A counter counts the number of containers added to the retort. The product
containers fall into the water to limit container damage. The containers are jumble
stacked in the retort. When the preset number of containers have entered the retort the
containers are automatically diverted to the next retort to be filled. The hydraulic push
button operated top sliding door of the retort is then closed. Steam is admitted to the
retort through a spreader in the top of the retort, forcing out the cushion water which is
normally collected, reheated, and reused. In some plants the cushion water is gravity
drained before venting. The drain is left open until all cushion water has been removed
from the retort and venting conditions met. Newer models of crateless retorts are
normally equipped with a false bottom door at the exit end (bottom) of the retort. The
false bottom door is perforated with holes which allow for a flow of steam between the
false bottom door and the discharge door. The false bottom door also prevents containers
of product from contacting the condensate which may build up in the bottom of the retort.
Condensate is removed from the bottom of the retort through a condensate bleeder
(normally 3/8" or larger) normally located in the bottom door of the retort. A 1/8" bleeder
is recommended between the false bottom door and the condensate bleeder to provide
visual assurance to the operator that there is no condensate buildup in the retort during
thermal processing. Some older systems may still be encountered which do not use a
false bottom and/or employ a second 1/8" bleeder. These systems should be carefully
evaluated to determine that the condensate is being removed from the retort during
thermal processing.

6
After the cushion water has been removed from the retort using the steam forced method,
the retort is vented for a short period of time (this must be established by a processing
authority). The processing of the product normally starts when the retort reaches
processing temperature, but not before a free flow of steam is noted from the 1/8 bleeder
located between the false bottom door and the discharge door. Failure of condensate
bleeders to function properly in these retort systems has caused several instances of
improperly processed LACFs. Condensate buildup in the bottom of the retort may contact
only a few cans in the bottom of the retort, causing underprocessing of those containers.
Such a situation can result in a very few cans of underprocessed product in a large lot of
containers. After the product has been processed cooling water is normally brought into
the retort to partially cool the product. In some systems, the product is dumped from the
bottom of the retort into a cooling canal. The discharge door on some systems is below
the level of the water in the cooling canal. This causes a vacuum to be formed in the
retort and the cans drift slowly out of the retort into the cooling canal. A chain in the
cooling canal then moves the container through the cooling water to the unscrambling
station. In some of the older crateless retort systems, containers were dropped into the
cooling canal through a vibrating basket on the retort or directly onto a chain conveyor.
Excessive container damage was sometimes noted in those systems.

Figure 3

7
STILL WATER IMMERSION RETORTS

Equipment and procedures for pressure processing in water in still retorts are covered by
9 CFR 431.6(c)(1) of the LACF regulations. The requirements for still water immersion
retort systems (Figures 2 and 4) would also apply to those agitating systems used in the
still non-agitating mode.

Figure 2

Thermal processing of glass, plastic, laminated pouch, and large profile metal containers
require that an overpressure greater than the pressure created by the retort temperature be
provided to maintain container integrity. Pressures in the range of 20 to 32 psig are
normally used for glass containers. When the product in a container is heated to high
temperatures, pressures exceeding those of the retort can be created in the container. This
higher pressure is due to the combination of increased vapor pressure and expansion of
the contents in the container. In the case of small metal cans, the metal can may be able to
withstand these pressures without permanent distortion of the metal in the can. In the case
of glass jars and other less durable containers, an overpressure must be used to prevent

8
the container from venting the contents, or becoming permanently distorted or destroyed.
The water immersion still retort was first designed for use in processing glass jars. Water
immersion still retorts are now used to process a variety of containers requiring an
overpressure. In some cases, the water immersion retort may be used to process small
metal containers as well. If the water immersion retort is used to process metal containers
there is some concern with the rusting of containers caused by the addition of air to the
processing water.

Basically there are four principle differences in a still retort equipped for pressure
processing in water as compared to a still steam retort:

- Compressed air must be provided to the retort to create the overpressure during
processing and cooling.
- A pressure control valve must be added to the retort.
- The temperature of the retort must be controlled independently of the pressure.
- The containers are processed and cooled under water.

Figure 4

9
The water level in the retort must be maintained to provide water above the top level of
the containers at all times. It is recommended that the containers be covered by at least 6
inches of water. If the water level falls below the level of the top containers those
containers exposed to the steam/air mixture in the top of the retort must be identified and
set aside for reprocessing or evaluation by a processing authority. A water level indicator
is required on all water immersion retorts. This can be in the form of a water glass sight
tube, pet cocks, or mechanical indicator. A low-water alarm (visual & audible) is
suggested. The operator must observe the water level during processing to insure that the
water does not drop below the level of the top containers. At a minimum, observations
should be made and recorded at the start of the process and at the end of the thermal
process prior to the addition of cooling water to the retort. A non-clogging water tight
drain valve is required to prevent leakage of water from the retort during processing. It is
suggested that this valve be screened to protect the valve from being clogged with broken
glass and other debris.

Heating and circulation of the water to provide for uniform thermal processing
temperatures in the retort system is important.

Steam introduction into the bottom of vertical retorts can be accomplished in one of
several satisfactory ways. One way is by using a steam spreader equipped with six pipes
radiating out from the center with "fish tail" nozzles which direct the flow of steam up
along the sides of the vertical retort outside of the crates. A second acceptable method is
to use a 4 legged cross steam spreader in which each pipe is perforated with holes
directed 15° below horizontal along one side only. The legs are arranged in opposing
pairs so that the holes face each other to give alternate live and dead quadrants. This
arrangement provides for circulation of the water in the retort. In horizontal retorts, the
steam distributor should run the full length of the retort with perforations distributed
uniformly along the pipe. Several still water immersion retorts of European design inject
steam directly into the water circulation line to maintain the processing temperature. Any
of the above, or other methods, are appropriate as long as there is documentation in the
form of temperature distribution data or other documentation from a processing authority
that supports the method of heating the water.

Circulation of the water is important to provide uniform temperature throughout the

retort. Adequate circulation of the processing water by air or pump must be established
through procedures recognized by a processing authority.

Air is added to the steam supply line prior to the steam spreader in vertical retorts to aid
in the mixing of the water. As the air is added with the steam, it also prevents steam
'knock" or "chatter" (a loud bumping sound) in the retort which happens when live steam
is introduced into water. The air and steam mix to form bubbles out of the steam
distributor. As the bubble moves up through the water the heat from the steam is lost to
the water. The air that remains reaches the top of the vertical retort to provide the air
overpressure. Excess pressure is released through the pressure control valve. A large flow
of air (15 to 18 cubic feet per minute) is needed during the initial heating and come-up
phases of the retort. This may be provided through an air bypass line. When the retort

10
processing temperature is reached the flow of air can normally be reduced to (4 to 5
CFM). Air flow is normally regulated by placing an orifice in the line which provides a
certain air flow at a regulated pressure. The air flow to vertical retorts should be
documented during establishment of the temperature distribution in the retort. The air
flow should be verified by the establishment using a flow meter at intervals sufficient to
insure that the retort is operating under the parameters used to establish the temperature
distribution in the retort.

For horizontal retorts, a water circulation system is recommended. This system uses a
pump to draw water out of the bottom of the retort through several screened openings
(suction manifold) and to discharge the water over the entire length of the top of the retort
through a water spreader. The pump should be capable of circulating the entire volume of
retort water at least every 4 to 5 minutes. A pilot light is normally used to indicate that
the pump motor is running. Even though the light indicates that the pump motor is
running, it does not insure that the water circulation is adequate. Plugged lines, bent
impellers on the pump and other mechanical problems may not be indicated by the pilot
light. A flow meter on the circulation line is recommended to provide a true indication of
water flow in the circulation line. Air must still be added to the horizontal retort to
provide for the overpressure during processing.

Vertical still water immersion retorts are required to have centering guides, which should
be installed so as to insure that there is a clearance of approximately 1 1/2" along the side
of the retort to provide for circulation of the water during thermal processing and cooling,
in addition to crate supports.

Containers are normally added to vertical retorts that contain water at or near the same
temperature as the initial temperature of the product. If product in glass jars is subjected
to water which is too cold, thermal shock may break the containers. If the water in the
retort is more than 15° F above the temperature of the container, the glass container
closure may vent product. Water must be added to horizontal retorts after the containers
are loaded. A separate warm water supply at or near the initial temperature of the product
which can be used to fill the retorts aids in more rapid production of glass containers. If
the water added to the retort is below the initial temperature of the containers, measures
must be taken to insure that the initial temperature in the container is not lowered, or that
the temperature of the water is used as the initial temperature. Several retort systems use
hot water storage tanks located above the processing shell. The temperature of the stored
water is dependent upon the container to be processed, and may range from several
degrees above the thermal processing temperature for metal cans to only a few degrees
above the initial temperature of glass containers. Following processing, a portion of the
processing water is forced back into the upper storage drum and reheated for processing
the next batch.

Cooling water is normally added to the circulation pump line on horizontal retorts or
through a cooling ring above the containers in a vertical retort. It is important that glass
containers are not subjected to a severe thermal shock to prevent glass breakage.
The overpressure must be maintained in the retort until the pressure in the container falls

11
to levels which do not cause container failure. Overpressure may be critical to the thermal
process for large profile half steam tray metal container and retortable flexible pouches.
The overpressure maintains the container profile and holds the container against the
product allowing for more efficient heat transfer from the container to the product. When
overpressure is listed as a factor critical to the thermal process, a record of the process
pressure must be made. The overpressure used during thermal processing should be the
same as that used during establishment of the thermal process or as recommended by the
firms processing authority.

It is recommended that the temperature probe in water immersion retorts be located next
to the MIG thermometer, except in vertical retorts which are equipped with a
combination recorder/controller. The controller bulb in these vertical retorts must be
located in the bottom of the retort beneath the lowest crate rest in such a position that the
steam does not strike it. This should be the coldest spot in the vertical retort. In a
horizontal retort the recorder/controller probe should be located between the water
surface and the horizontal plane passing through the center of the retort so that there is no
opportunity of direct steam impingement on the control bulb.

Some water immersion systems may be set up to process in both steam and water. Those
systems must be carefully evaluated to insure that they meet the mandatory provisions of
both sections of the LACF regulations.

CONTINUOUS AGITATING STEAM RETORTS

Equipment and procedures for processing in continuous steam retorts are covered by 9
CFR 431.6(b)(3) of the LACF regulations.

These systems provide for continuous container handling with intermittent product
agitation. Continuous agitating steam retorts are manufactured by FMC (Sterilmatic) in
the U.S. and Europe and by Stork (Steristork) in Europe. The basic design of both
systems is similar (Figure 5).

The retort systems are made up of a series of processing vessels called shells. The
arrangement and number of shells is dictated by the product, production capacity, and
space limitations in the establishment. Common arrangements found include: Two-shell:
one pressure cooker and one pressure cooler; three-shell: one pressure cooker shell, one
pressure cooler shell and one atmospheric cooler shell; and four-shell: preheater shell,
one pressure cooker shell, one pressure cooler shell and one atmospheric cooler shell.
Specialized systems may have up to seven shells. The shells can be arranged side by side
or offset end to end depending upon the available establishment space.

Containers are fed mechanically through the series of at least one heating and one cooling
shell. Within each processing shell is an open, closely fitting rotating reel which runs the
length of the vessel. Cans are carried horizontally in channels made up of angles, usually
of stainless steel, welded around the perimeter of the reel. A spiral T-track is welded to

12
the inside of the shell spaced at intervals slightly larger than the can length. As the reel
turns the containers are forced against the spiral T which causes the cans to move down
the length of the retort while being carried by the reel. The containers are fed into the
processing shell or preheater through a pocket valve; a rotary transfer valve which is
timed to the reel and designed to prevent loss of steam from the retort (Figure 7).

Figure 5

Figure 7

There is a wheel at the exit end of the retort and into a second transfer valve which
transfers the cans to the next processing or cooling shell while maintaining processing

13
pressure if needed. All of the shells are driven by one variable speed motor or drive
mechanism through a series of interconnecting gears to insure that the reels are timed to
each other. The drive mechanism is required to be locked or protected by a sign that
states that only authorized persons are to make adjustments.

Because of the physical limitations of the reel and spiral T these retort systems are
normally limited to a narrow range of can sizes. The length of the can going into the
retort can not be longer than the maximum distance between the spirals in the T. The
diameter of the can is limited by the distance between the steps in the reel. The number of
steps (number of cans around the diameter of the reel) is determined by the can size and
the diameter of the reel. For the FMC systems these steps are standardized for can sizes
(unless the system has been altered or custom built). The number of steps can be used
along with other information to calculate process time.

STEPS PER TURN OF REEL FOR STERILMATIC CONTINUOUS AGITATING

RETORTS

Steps per
Can Size Turn of Reel
211 56
300-303 47
307-401 42
404 36
603 24

The container capacity is normally stamped on the end of the shaft of the processing
shell.

The length of the process is controlled by the capacity of the retort and the speed at which
the reel is turned. The capacity is determined by the length of the retort shell and the
number of steps in the reel.

By knowing the retort capacity, the number of steps in the reel and other processing
information the following formulas can be used to determine reel speed or process time:

Seconds for 10 reel revolutions = (10 rvs) x (60 secs) x reel steps x process time/capacity
Example: (10x60x47x10)/4136 = 68.18 seconds for 10 revolutions

Containers per minute = Capacity/Process Time

Example: 4136/10 = 413.6 seconds

Revolutions = Capacity/(reel steps x cook time)

Example: 4136/(47x10) = 8.8 revolutions per minute (RPM)

Seconds for 10 revs = (10 revs x 60 secs x reel steps)/(cans per minute)

14
or (10 revs x 60 sec)/RPM
Example: (10x60)/8.8 = 68.18

The actual process time is determined by using a stop watch and timing 10 revolutions of
the retort reel. One arm on the retort reel is selected and observed to pass a stationary
mark on the retort shell for the required number of revolutions. Reel speeds that are too
fast will cause the product to move through the retort at a faster rate shortening the
process time. A reel speed that is too slow increases the process time but may reduce the
agitation of the product and reduce the thermal process given to the product. The process
is normally designed with the slowest reel speed (minimum agitation) taken into account.

The rotational speed of the retort shall be specified in the process schedule. The speed
shall be adjusted as specified, and recorded by the establishment when the retort is
started, and checked and recorded at intervals not to exceed 4 hours to ensure that the
correct retort speed is maintained. Alternatively, a recording tachometer may be used to
provide a continuous record of the speed. If a recording tachometer is used, the speed
shall be manually checked against an accurate stopwatch at least once per shift and the
results recorded. A means of preventing unauthorized speed changes on retorts shall be
provided. For example, a lock or a notice from management posted at or near the speed
adjustment device warning that only authorized persons are permitted to make
adjustments are satisfactory means of preventing unauthorized changes.

The standard continuous agitating retort systems are designed to operate over a wide
range of temperatures up to 275° F (135° C), with custom designs operated at
temperatures of up to 294° F (146° C).

Steam is fed into the bottom of the sterilizer through a steam manifold to a steam trough
in the bottom of the retort. The condensate that forms in the bottom of the retort from
cold containers continuously entering the retort must be removed to prevent the
condensate from building up and touching the containers. This not only cools the
containers but may prevent agitation of the product in the containers. Condensate is
normally removed during venting by opening the drain valve in the bottom of the retort.
After the retort is up to processing temperature, continuous draining of the condensate is
through a 3/4 inch drain valve left partly open or through an automatic condensate trap. A
1/8 inch (minimum) bleeder is required in the bottom of the steam trough to provide
visual assurance to the operator that there is no condensate buildup in the retort.

Venting of the retort takes place at the beginning of the production period and need not
be performed again as long as the retort is not cooled. Venting should be performed as
per the retort manufacturers or processing authority’s instructions. The FMC continuous
retort is normally vented for 7 minutes to 220° F through the two 2-inch vents located in
the top portion of the retort shell. If the retort shell has to be cooled for repairs or is
stopped and cooled for any other reason, the retort must be vented when it is brought
back up to processing temperature.

Air is removed from the retort during processing by the continuous operation of bleeders

15
which are located within one foot of the outermost product at each end of the retort and
not more than 8 feet apart along the top of the retort.

Agitation in this system is intermittent axial agitation. The container rotation can be
divided into three phases (Attachment 7) consisting of fixed reel, sliding rotation, and
free rotation. The headspace bubble, provided by the gases in the headspace, moves
through the product to provide agitation and increased rates of heating in the product
during periods of rotation. Maintaining the headspace filed as part of the process schedule
insures a headspace bubble. In the fixed reel portion of rotation the container is carried by
the reel through the top 260° of rotation. During this phase no or little agitation of
products occurs. As the container approaches the lower 140° of rotation in the retort shell,
it starts to contact the spiral "T" welded to the interior of the retort shell and begins to
turn. This sliding rotation transition phase lasts for approximately 20° of rotation and
provides some product agitation. As the container enters the lower 100° of rotation (free
rotation phase), the container contacts the retort shell and rotates freely. The majority of
agitation occurs in this phase. As the container starts up the side of the retort, sliding
rotation takes over and changes to the fixed reel phase. Agitation is dependent upon
control of factors such as: headspace, consistency, reel speed and fill weight which must
be controlled during processing.

Intermittent agitation will increase the heating rate of the product only if the headspace
bubble is free to move. Solid pack products will normally not benefit from an agitated
process. Some manufactures will still use the continuous retort to process products based
on a non-agitating process because of the convenience of the container handling in the
continuous system. For products where agitation is not taken into consideration during
establishment of the process, headspace may not be critical to the process.

When checking reel speed there are usually two speeds of concern. During process
schedule establishment, the minimum reel speed is studied. Then process schedules are
recommended to the manufacturer. When the manufacturing firm sets the retort to meet the
process schedule, the reel speed may need to be different to meet the process. For example,
the RPM for meeting a time of 15 minutes may be 4.2 RPM whereas the minimum RPM is
3.5. The actual RPM should never be less than the minimum RPM and the actual RPM
should assure that the process schedule time is achieved.

Following thermal processing in the processing shell, the containers are transferred through
a pressure transfer valve to either a pressure cooler or an atmospheric cooler depending
upon process temperature and can size. Some containers can be cooled in a Micro-cool
valve, where water is sprayed on the containers, to a low enough temperature to allow for
atmospheric cooling. The pressure cooler and or Micro-cool valve must be operated at a
pressure at least 2 lbs below that in the processing shell to prevent air and water from being
forced out of the cooling shell or valve into the thermal processing vessel. The closed
cooling shell is approximately 2/3 full of water to provide flood cooling of the containers.
Some systems also use an atmospheric open or half-shell cooler where water is sprayed
over the containers. The cooling water normally enters the can exit end of the cooling shell
and flows to an overflow on the can entry end of the cooling shell. This provides for

16
counter flow cooling of the containers. Additional cold water is added to control the water
temperature and to maintain the water level in the cooling shell. The temperature of the
cooling water at the can entry end of the cooler is normally at a very high temperature (>
200° F) as the hot cans enter the water.

The heating of the cooling water as it passes over the containers tends to drive off chlorine
if it is used to sanitize the cooling water. A measurable level of chlorine may not be found
in the cooling water at the water discharge point of the cooler shell. If the quality of the
water in the cooling shells is not maintained by good sanitary practices such as; sanitation
of the cooling water, routine draining and replacement of the cooling water, and cleaning
of the cooling shell, excessive microbiological growth in the cooling shells may cause
post processing contamination.

If the retort jams or breaks down during processing operations, necessitating retort
repairs, the retort must be operated in a manner that ensures commercial sterility of the
product. The retort can be operated as a still retort per 431.9(c)(1)(vi)(A)(1). All
containers can be given a still emergency process using a process supplied by the firms
processing authority. Any containers in the intake transfer valve and any containers in
transfer valves between processing shells have to be removed, given a still process,
opened and reprocessed or destroyed. Complete records of the still process must be
maintained.

If a temperature drop occurs in the retort the temperature drop should be handled per
431.9(c)(1)(vi)(A)(2). The retort should be equipped with an automatic device to stop the
reel when the temperature drops to below the specified process temperature.
If the temperature drop was 10ºF or more the reel must be stopped and all of the
containers must be given a still process as above, discharged and reprocessed, repacked
and reprocessed or discarded. If the temperature drop was less than 10ºF, an authorized
emergency still process may be used prior to restarting the reel, or container entry to the
retort can be stopped and authorized emergency agitating process used. Complete records
of the handling of temperature drops must be made.

These systems may be installed with modifications which will allow unique processing to
take place. Known system modifications include: the addition of dual spiral construction
which allows for the processing of two container sizes at the same time using the same
processing conditions; the use of metal carriers to hold and transport glass containers
through the system; the use of steam air mixtures to thermally process LACF; and the use
of the continuous retort system as a water immersion retort with steam over-pressure.
When modified continuous cookers are encountered, the inspector must insure that the
retort installation and operation meets the requirements of the firm’s process schedule
and the LACF regulations.

DISCONTINUOUS AGITATING STEAM RETORTS

Equipment and procedures for pressure processing in steam in discontinuous agitating

retorts are covered by 9 CFR 431.6(b)(2) of the LACF regulations.

17
These retort systems are batch systems which provide for either continuous axial
agitation of the product or end over end agitation of the product during thermal
processing and cooling of the containers. The most common axial agitation batch retort in
the United States is the FMC Orbital (Orbitort) Sterilizer. This system was designed to
process large institutional size (603 X 703, #10) cans of medium viscosity products such
as cream style corn. Other sizes of cans can be processed with modifications to the
system.

The orbital sterilizer does its pressure processing and cooling in one shell. The sterilizer
consists of a horizontal retort shell which contains an outer reel to which a spiral has been
attached, and an inner reel which contains the container channels or steps.

During loading, cans are fed into the retort through a large air-operated gate valve located
high on the retort wall. The outer spiral reel is locked to the retort shell. The inner reel is
turning during loading causing the containers to move toward the exit end of the
sterilizer.

A counter keeps track of the number of containers loaded into the retort. A second
counter advances the cans two turns separating processed and unprocessed cans by two
spiral turns. This is a safety factor to keep unprocessed and processed cans separate. At
the same time that containers are being loaded, processed containers are being unloaded
through an air-operated gate valve located low on the exit end of the retort shell. When
the retort is full the loading/unloading gates are closed, the outer "spiral" reel is locked to
the inner "channel" reel holding the containers in place during thermal processing and
cooling.

The retort is vented per the processing authority or equipment manufacturers’

recommendations. Documentation that adequate venting is achieved must be kept on file
by the processor. At the time that steam is turned on, the drain must be left open for
sufficient time to remove the steam condensate from the retort, and provision should be
made for continuing drainage of the condensate during the retort operation. It is important
to remove the condensate so that the containers do not contact condensate build up in the
bottom of the retort which could cool the containers during thermal processing.

During thermal processing any air coming in with the steam is removed from the retort
through bleeders located within one foot of the outermost container on each end of the
retort and no more than 8 feet apart along the top of the retort or through some other
arrangement proven to be satisfactory by temperature distribution studies.

At the conclusion of the thermal processing cycle, cooling water is introduced into the
retort while the containers are still being agitated. When the product is cooled the retort is
ready for emptying and reloading.

The product agitation in this retort system is produced by forcing the head space bubble
through the product at very high (approximately 35 RPM) reel speeds (Figure 8). High
speed rotation is possible because the containers are locked in place. The speed of the

18
retort must be adjusted as necessary to agree with the speed of the retort listed in the
process schedule. The rotational speed as well as the process time must be recorded for
each retort load. A recording tachometer may be used to provide a continuous record of
retort rotational speed. The accuracy of the recording tachometer shall be determined and
recorded at least once per shift by checking the retort or reel speed using an accurate
stopwatch. A means of preventing unauthorized speed changes on retorts shall be
provided. For example, a lock or a notice from management posted at or near the speed
adjustment device warning that only authorized persons are permitted to make
adjustments are satisfactory means of preventing unauthorized changes.

Figure 8

Factors critical to obtaining the induced agitation in these systems include: maintaining
the correct headspace, product consistency, minimum machine vacuum in vacuum
packed products, maximum fill-in or drained weight, and percent solids as specified in
the process schedule.

DISCONTINUOUS AGITATING WATER IMMERSION RETORTS

Equipment and procedures for processing in discontinuous agitating water immersion

retorts are covered by 9 CFR 431.6(c)(2) of the LACF regulations.
These are batch retort systems which provide for continuous product agitation by
movement of the head space bubble during thermal processing. Agitation in these
systems is normally induced through end over end rotation of the container (Figure 8) as
opposed to the axial rotation of the container in the FMC continuous and orbital retorts

19
previously discussed. Because of the rotational axis of various containers in the baskets
during processing, the containers against the outside walls of the basket may receive
more agitation than those in the center of the basket.

Discontinuous agitating water immersion retorts are manufactured by AlIpax Products

Inc. in the United States under an agreement with the Maskinfabrikken Phoenix
subsidiary of the Klinge group in Denmark. Known manufacturers of these systems in
Europe include: Herman Stock in Germany, Lubeca in Germany, and Phoenix in
Denmark. All of these systems are or have been available for installation in the United
States through U.S. distributors. The Stock Rotomat is one which has been distributed for
a number of years, with numerous installations in the U.S. and world wide.

The majority of these systems operate in a similar manner. These systems can be found
with a wide variety of valve types and plumbing arrangements. The valves and plumbing
may be changed for custom installation by the manufacturer or installer of the equipment
to provide additional functions or for better operation of the system. Many of the early
Rotomat retorts were equipped with on/off steam control valves which have been
replaced with modulating steam control valves to provide for better control of the retort
temperature. Retort systems now entering the U.S. are often modified to meet the U.S.
requirements for MIG thermometers and instrumentation, and to replace the control
valves on the retort. The configuration of the retort must be carefully reviewed during
inspection of these systems.

Discontinuous agitating water immersion retorts can be used for the processing of
numerous container types including: metal cans, glass jars, and plastic containers and
unusual container shapes such as semi-rigid plastic bottles, flexible pouches and half-
steam table trays.

The processing system consists of two pressure shells or drums, one sitting on top of the
other. The top drum is used to store and preheat the processing water. The lower drum is
the processing drum (Figure 9).

Containers are loaded into crates or specially designed racking systems depending upon
the container type. The crates are then loaded into a reel within the lower retort shell and
locked into place during processing.

Water in the upper drum is heated by steam prior to processing. The temperature of the
stored water is dependent upon the type of container to be processed, and may range from
several degrees above the thermal processing temperature for metal cans to only a few
degrees above the initial temperature of glass containers. Storage drum temperature may
be critical to achieving adequate temperature distribution. To achieve correct temperature
distribution in the retort, the firm must meet the minimum temperature requirement.

20
 Figure 9

Processing in the Rotomat retort system is designed to proceed through a series of

programmed phases which may consist of several steps within each phase. The steps
normally encountered include:

- Heating of the upper storage drum

- Sterilization I - in older models this includes dropping the heating water and
heating the water to processing temperature, in later models this involves only
dropping the processing water.
- Sterilization II – in earlier models this is the sterilization (hold) phase, in the later
models this is the heating phase to process temperature.
- Sterilization III – this is the sterilization phase in later models.
- Pressure cool I – this is the initial cooling phase where the process water is
recaptured
- Pressure cool II – this is the final cooling stages.
- Open door – retort is ready for unloading

The phases and steps used may vary with the make of retort system used, the model of
the retort used, the control system used, and the product being processed. It is important
to determine the retort steps and sequencing during the inspection. This information
should be compared to the information in the process schedule.

These retorts may be equipped with a wide range of control systems depending upon the
manufacturer, model and customer specifications including: manual controls, semi-

21
automatic electronic relay controls, electronic card readers, electronic pre-programmed
logic controls and microprocessor controls.

At the beginning of the sterilizing cycle, water from the pressurized upper drum is
dropped into the lower processing drum through a connecting pipe and valve. At that
time, the circulation pump begins to circulate the water by drawing the water out of the
bottom of the retort through a suction manifold (also called the "circulation channel") and
returning the water through a distribution manifold in the top of the lower drum. The
returns located in the bottom of the retort shell should be screened to prevent debris from
entering the water circulation system. As the water is circulated, it passes through a steam
injection chamber where live steam is injected into the water to maintain processing
temperatures.

When water enters the lower drum, air must be expelled to make room for the water. This
is done through a purge valve (some times called a vent valve by the firm). If the purge
valve is not open for a long enough time period, air will remain in the lower drum and the
lower drum will take a longer time to fill with water. If the purge valve is open too long,
the hot water will flash to steam, and water and steam will be lost out of the purge valve
lowering the temperature in the processing vessel. This may cause the come-up period to
be extended to reach processing temperature, and has been reported in some cases to
affect temperature distribution in the retort system. The length of time that the purge
(vent) valve is open is determined by the processing authority and normally programmed
into the retort controls as a set time period.

The come-up time (CUT) prior to processing is very important in this type of retort.
During the CUT the retort is brought up to processing temperature and the water
temperature throughout the retort is stabilized at or above the process schedule
temperature. This may require a CUT which extends beyond the time when the
processing temperature is first reached, as indicated by the retort instrumentation. Usually
both a time and temperature are required to be met to fulfill CUT requirements. If CUT is
used in establishing the process schedule, it must be part of the process and controlled as
a critical factor. If CUT is only critical based on the temperature(s) and time(s) required
to achieve adequate temperature distribution, it is not part of the process but still must be
controlled and recorded as part of the processing record. CUT varies by retort model and
make, and for different products.

In the sterilization (hold) phase, the product is held for at least the minimum time at the
minimum temperature specified in the process schedule.

When the thermal process is complete cold water is introduced into the lower drum
through the water distribution system or through a separate pump. This cold water forces
a portion of the hot processing water back up into the top storage drum where it is
captured and reheated for the next process.

The water circulation pump is the principle device for insuring adequate temperature
distribution in the retort. Temperature distribution and heating programs are normally

22
established at the maximum flow rate. If the water distribution system becomes clogged
or the pump is damaged or worn, the flow rate may decrease. Severe drops in flow rate
may be indicated by temperature drops in the retort. However, this may not be the case
for less severe flow rate changes. Most of the systems are equipped with at least a pilot
light that indicates that the pump is in operation. Some of the newer systems also
incorporate a pressure differential alarm, which measures the difference in pressure from
one side of the pump to the other, and alarms if the pressure differential falls outside of
preset limits. Neither of the above methods measures the actual water flow in the system.
A flow-indicting device is recommended for this purpose.

Rotation in the retort may be fixed at one speed, allow for selection of several speeds, or
may be variable over a wide range of speeds. The newer systems may allow for rotation
to be in either direction, to provide a rocking motion agitation, and provide for the
baskets to be in different positions during come-up and processing. The systems are
normally operated between 6 and 46 RPM. For those systems which do not take agitation
into consideration when establishing the process, it is still recommended by some
authorities that the reel be rotated at a minimum speed to enhance mixing of the
processing water and to maintain proper temperature distribution. Temperature
distribution must be documented for those systems operated in the still mode. Timing of
the rotation is done either through the use of a stopwatch and observation of rotation of
the driving mechanism on the rear of the retort, or through the use of a recording
tachometer. The accuracy of the recording tachometer shall be determined and recorded
at least once per shift by checking the retort or reel speed using an accurate stopwatch.
The rotational speed of each retort load must be recorded.

Overpressure during processing (to maintain container integrity) is supplied to the

majority of these systems by using compressed air. The majority of the retorts are
equipped with both a valve for supplying additional air and a valve for releasing excess
pressure (small vent or purge valve). This allows for more uniform control of
overpressure processing. The Stock systems normally use steam pressure in the upper
drum to provide over-pressure through a connecting valve to the lower drum. Stock
systems can also use air for overpressure if requested by the customer. Stock claims that
when steam is used in the lower shell to provide an over-pressure that deviations are not
normally caused by lower than normal water levels in the processing shell of agitating
retorts, as the head space will provide a steam processing medium. There is some
question as to whether the head space is pure steam or a mixture of steam/air which may
not provide a uniform temperature. When lower than normal water levels are noted, the
manufacturer should treat the process as a processing deviation; requiring the
reprocessing of the product, the destruction of the product or the review of the thermal
process by a processing authority unless there is documentation on hand to support
processing with lower than normal water levels.

The majority of the systems noted have been equipped with a water sight glass or
mechanical indicator of water level in the retort as well as being equipped with electronic
alarms for low-water levels.
Adequate temperature distribution in the batch agitating water immersion retort is

23
dependent upon such factors as the proper functioning of the centrifugal pump, rotation
of the reel, and the number of cages in the retort. A minimum number of cages full of
containers (e.g. 3 cages in a 4 cage retort) is required to maintain the water level in the
retort. The number of cages also affects the CUT (come-up time) to the processing
temperature. If the minimum number of product filled crates are not available the firm
may use ballast (e.g. containers filled with water) to fill the additional crates required. In
addition, the open area provided by divider plates or spacers, as well as the cages or racks
themselves, can have an affect on adequate temperature distribution. Any change to a
more restrictive-to-flow design in any of the above must be validated by new temperature
distribution studies. Temperature distribution may be affected by container type,
container size, racking configurations, number of containers in the retort, product being
produced and many other variations in thermal processing. Because of the many variables
that can influence temperature distribution in these retorts in some cases each retort, each
containers type, each racking system and each container size will have to be evaluated to
determine their effect on temperature distribution.

Delivery of the process schedule is also dependent upon the control of critical factors
such as: headspace, product consistency, fill-in or drained weights, vacuum in vacuum
packed products, minimum net weights, percent solids and other critical factors identified
in the process schedule.

HYDROSTATIC RETORTS

Equipment and procedures for pressure processing in steam in hydrostatic retorts are
covered by 9 CFR 431.6(b)(4) of the LACF regulations.

Generally the hydrostatic retort can be thought of as a still steam retort operated at a
constant temperature through which containers are conveyed by a continuous carrier
chain at a constant rate designed to provide the correct process time (Figure 10).

Figure 10

24
Hydrostatic retorts are manufactured by the FMC Corporation in the U.S. and by Stork
and others in Europe. Newer designs now offer end over end or axial agitation of the
product; the use of overpressure for the maintenance of container integrity; the ability to
process glass and flexible pouches; and water as a heating medium in addition to steam.
The systems are used for high volume products which need long cook times such as
condensed soups and pet foods.

The name hydrostatic is derived from the fact that the pressure in the steam dome is
counter balanced by water in the entry and exit legs of the retort. The higher the water
level, the higher the pressure and temperature obtained in the steam dome. For example,
the water height in the water legs must be 37 feet high at sea level to counter balance a
processing temperature of 250° F (121° C). Operating at temperatures above 250° F will
require a higher water level. The retorts can be operated below the maximum temperature
as long as the pressure remains high enough to prevent water contact with the containers
in the steam dome.

Start up procedures for a hydrostatic retort requires venting of the retort and bringing the
water in the feed legs up to temperature. This procedure takes a longer period of time
than the venting of still steam retorts. The hydrostatic retort is normally operated for
periods of up to several weeks and may be shut down and cooled only when required for
maintenance or repairs.

These retort systems are very large and normally extend several stories into the air.
Containers are loaded into a horizontal carrier on the continuous chain and conveyed up
to the inlet leg of the sterilizer. The inlet leg is filled with water which counter balances
the pressure in the steam dome. The temperature of the water increases as the container
moves from the top of the inlet leg down toward the steam-water interface at the bottom
of the leg. Water temperature in the inlet leg may range from ambient to boiling. The feed
leg may contribute to the process lethality by increasing the initial temperature of the
product. If process lethality is claimed for the inlet leg of the retort, the water temperature
in the inlet leg must be carefully controlled. The container is conveyed through the steam
water interface into the steam dome. The number of times that the carrier passes through
the steam dome as well as the speed of the carrier determines the process time. Traveling
from the top of the steam dome to the bottom, and vice-versa, is referred to as one pass.
Hydrostatic retorts with 2, 4, 6, and 8 passes are common. After traveling through the
steam dome the containers are conveyed into the exit water leg where the temperature
decreases as the container passes up the leg. The cans leaving the steam dome are heated
to a high level and give up their heat to the water in the discharge leg. This results in
several situations depending upon the design of the retort:

- The water in the discharge leg ranges from 215° F near the steam-water interface
to 212° F near the top of the leg, and the water quietly boils and steam is
discharged from the top of the leg.

- Cross circulation pumps are used to pump the hot water from the base of the exit
leg to the base of the inlet leg and from the top of the inlet leg to the top of the

25
 exit leg, stabilizing the temperatures in the legs.

- Water is pumped from the base of the exit leg through a heat exchanger with the
cooled water being returned to the top of the exit leg.

Any of the above three methods of operation are acceptable.

As the container exits the leg it is exposed to atmospheric pressure, and it may pass
through a series of water spray coolers to further cool the product. The conveyor chain
carries the containers back to near the loading station where the processed product is
unloaded from the continuous carrier. Because the container inlet and exit are close
together, care must be taken to insure that unprocessed containers do not become mixed
with processed containers. Containers found on the floor or elsewhere whose status is
questionable should be destroyed.

Control of the water levels in the feed and exit legs are important to maintain the
hydrostatic pressure in the retort. The water level is normally controlled through a
differential pressure controller which adds water when it is needed and dumps excess
water from the legs. Water level fluctuation in the feed and exit legs may be caused by
fluctuations in the feeding and discharge of containers. As more containers are fed into
the container conveyor more water is displaced from the legs, a lack of production results
in a lack of containers in the legs and the water level falls.

Hydrostatic retorts have been installed with up to 3 carrier chains operating in the same
steam dome. This allows for the production of different can sizes at the same temperature
by adjusting the process time through the speed of the conveyor. Carrier chains designed
for cans can normally be used to process a number of different diameter cans within
limits (e.g., 211 - 303, 404 - 603).

Steam is fed into the steam dome, depending upon the manufacturer, either in the center
or top of the steam dome. Standard temperature or pressure controllers are normally used
to control the retort temperature. The control of retort temperature through the use of a
water level float has been used on some European systems.

9 CFR 431.6(b)(4)(i) requires that the MIG thermometer be installed in the retort steam
dome near the steam-water interface. This should be the coldest spot in the retort dome. If
the thermal process is based on lethality gained in the feed or exit water legs, a MIG
thermometer is required to be installed near the bottom temperature recorder in each
water leg (Figure 11).

9 CFR 431.6(b)(4)(i) requires the installation of additional temperature recorders near the
top and bottom of each hydrostatic water leg if the process schedule specifies
maintenance of particular temperatures in the water legs.

9 CFR 431.6(b)(4)(iv) requires the hydrostatic retort to be equipped with at least one
bleeder 1/4 inch or larger at the top of the steam chamber or chambers at the opposite end

26
of steam entry. In addition, all bleeders must be arranged in such a way that the operator
can observe that they are functioning properly.

The carrier conveyor in the hydrostatic retort may be numbered so that the location of the
carriers can be determined during processing. Carrier location becomes important if the
retort temperature/pressure falls to a level where the containers contact the water. The
retort should be equipped with an automatic stop if the temperature drops below the
minimum process schedule temperature. If the retort is stopped at that point, the operator
can identify those carriers in contact with the water. The containers in the affected
carriers can then be set aside for reprocessing, destroyed or held for evaluation by a
processing authority.

The carrier speed is controlled for each container conveyor through a variable speed
motor. Carrier conveyor speed may be measured by the number of flights per minute
using a stop watch or electronically by a sensing probe. Electronic measurement of the
conveyor speed should be verified by using a stop watch on a routine basis. The correct
container-conveyor chain speed can be determined in the following manner.

1. The desired carriers-per-minute is determined by dividing the desired process

time into the number of carriers in steam. Number of carriers in steam = Carriers-
per-minute Process time in minutes
2. Calculate the actual carriers-per-minute rate by timing 50 carriers with a stop
watch. Divide this time in seconds into 3,000 to get actual carriers per minute.
3,000/Second for 50 carriers = Carriers-per-minute

Figure 11

27
CASCADING WATER RETORTS

Equipment and procedures for processing in cascading water retorts are covered by 9
CFR 431.6(c)(1)(2) of the LACF regulations.

Cascading water retorts are known to be manufactured by the Food Processing

Machinery Division of FMC U.S.A. (Universal and Convenience sterilizers), Lubeca in
Germany (Lubeca Model LW406 and LW402 G), Herman Stock in Germany (Autovap
and Rotovap), Phoenix A/S a division of the Klinge Corporation in Denmark (Phoenix)
and by Barriquand in France (Steriflow). Copies of these retort systems may be made in
other countries. Custom built cascading water systems may also be encountered.

Figure 12

Cascading water retorts may be either still or end over end agitating batch type retorts.
They are normally operated with an air over-pressure and may be used to process a wide
variety of container types including glass, metal, plastic, and flexible pouches.

The Barriquand Steriflow has been the cascading water system most often encountered
by FSIS.

28
 Figure 13

The Steriflow is an over-pressure retort designed to operate at high temperatures, at or

above 130ºC (265° F), at pressures of up to 84 psig (5.9 kg/cm2), with very short cook
times. The overpressure is supplied by compressed air and controlled separate from the
retort temperature. The Steriflow uses less water for processing when compared to a
water immersion retort, (e.g., 100 liters per basket in the standard 1300 mm model retort).
At the start of processing, the process water is added to the bottom of the retort shell. A
gate in the bottom front of the retort shell prevents the loss of processing water when the
retort door is opened. During processing, this water is drawn from a trough in the bottom
of the retort by a centrifugal pump capable of recirculating the water in the system
approximately once every 9 seconds. The processing water passes through an indirect
heat exchanger where steam is used to heat the water to processing temperature. The
processing water then exits the heat exchanger and enters a water distribution manifold
above the crates and containers. The processing water is forced through a series of small
holes (e.g., 4 mm (5/16") on 21 mm (13/16") centers) in the manifold and cascades down
over the crates and containers. At the conclusion of the thermal process, cold water is
introduced into the heat exchanger to cool the processing water. The same water used to
process the containers is used to cool the containers. The cooling water in the heat
exchanger is never in contact with the containers. This provides for the use of low quality
water (such as sea water) in the heat exchanger as the cooling medium.

29
Water entry into the water distribution manifold has been noted to be at the center or the
end of the manifold in different models of the Steriflow. Location of the manifold water
entry may be important. Temperature distribution studies have indicated that the cold
zone in the retort may be affected by the location of the water entry.

Process water is normally used throughout a production shift prior to being replaced.
Small amounts of water may be added prior to each cycle to replace water lost when the
door is opened and product is removed.

In the standard 1300 mm retort, solid sided, perforated bottom 33" x 34" x 30" high retort
carts are normally used with perforated dividers [19 mm (3/4") on 25 mm (1") centers]
between layers. Container orientation is normally vertical. Container orientation, size,
shape and loading configuration may have an effect on temperature distribution.

Temperature and pressure may be controlled either by a cam programmer on older

systems, by a microprocessor/computer on newer systems, or by manual control.
Temperature is normally controlled through a Resistance Temperature Device (RTD)
located at the exit end of the heat exchanger. A second RTD located at the entry to the
circulation pump is used to drive the temperature recorder. A MIG thermometer should
be installed at this location. The entry to the water circulation pump has been selected as
the location of the coldest water being circulated in the retort during thermal processing.
Pressure is controlled separately through feed back from a pressure transducer and
operation of compressed air entry and pressure relief valves.

The production programs for some systems are designed to bring the coldest spot in the
retort up to thermal processing temperature through a series of time/temperature steps to
insure that the temperature in the retort is at or above the filed thermal processing
temperature at the time that the retort thermal process begins. An example of a stepped
program is as follows:

- Preheat water to 115° C (2390 F).

- Heat from 115° C (239° F) to 137° C (279° F) 6 minutes (must meet both time
and temperature).
- Heat for 136° C (277° F) 1 minute (time and temperature). This over-shoot
temperature is used to help achieve adequate temperature distribution in the retort.
- Heat for 135>° C (275° F) 1 minute (time and temperature).
- Heat for 134>° C (273° F) 5 minutes (scheduled operating process temperature).
- Cool

To obtain adequate temperature distribution the system is normally operated with a

temperature overshoot of at least 1°C above the process schedule temperature.

The stepped program varies with the retort, product and container. This program should
be part of the firm's process schedule. Documentation that the steps in the come up
portion of the retort program take place may be difficult. The come-up temperatures
sensed by the microprocessor may not be the same temperatures displayed by the MIG

30
thermometer and the temperature recording chart.

There are several areas of concern unique to the water cascade retort systems which
should be addressed when inspecting these systems.

- The come-up portion of the process must be designed to provide for adequate
temperature distribution (all parts of the retort are at or above retort temperature at
the start of the thermal process hold time). The come-up requirements may differ
from one product to another in the same retort, and from one container type to
another in the same retort. Ideally temperature distribution studies should be
performed on each retort model, each product produced, each container type used,
and on each individual retort installation to determine the come-up procedures.
The firm should have documented by temperature distribution studies that their
come-up procedures result in adequate temperature distribution in the retort prior
to the start of the timing of the process schedule.

- Care should be taken to determine the location of the control and recording
RTD5. The recording RTD has been noted to be installed in the exit end of the
heat exchanger. This may provide a recorded temperature higher than the coldest
temperature in the retort. At least one manufacturer now recommends that the
control RTD be located after the heat exchanger, with a feed-back RTD located at
the entry to the circulation pump. The latter RTD also drives the temperature
recording instrument. Both RTD5 should read at or above the process schedule
temperature prior to beginning the thermal process timing.

- FDA has noted that the Steriflow is not always equipped with a MIG
thermometer. When modified for a MIG thermometer, the MIG thermometer
should be installed in the inlet line of the circulation pump, next to the recorder
RTD, to monitor the temperature of the return cold water, which is the average
coldest spot in the retort. MIG thermometer lag will normally be observed during
the come-up steps.

- Water flow is not normally controlled as a critical factor. A pressure differential

may be measured between the pressure on the entry and exit ends of the water
circulation pump. This pressure differential alarms the control system if the set
limits are exceeded. The pressure differential is a measurement of the differences
in pressure on the two sides of the pump and may not measure a true water flow.
The pressure differential will indicate failure of the water pump but may not
always indicate a clogged water distribution system. A flow measuring device is
recommended to provide a more accurate measurement of actual water flow in the
system. Water flow in the system must be the same as that used during
temperature distribution studies in the retort.

- The holes in the water distribution manifold may become plugged with product or
mineral deposits. There should be a program in place for routine maintenance and
cleaning of return ports, the water distribution manifold, and water filter screens if

31
 present. During inspection of these systems, the water distribution manifold
should be examined to determine if the holes are plugged or have been reduced by
mineral scale buildup.

- The processing records maintained by the firm must document that operating
steps required to attain uniform temperature distribution in the retort during
thermal processing are being met. These steps should be listed as critical factors
on the firm's process filing form.

The Phoenix cascading water retort operates in a manner similar to the Steriflow. The
Phoenix retort system is offered in the U.S. by AlIpax Products Inc. Mandeville, La.
under the name Spray-Pax in still and rotational models.

Cascading water retorts manufactured by Lubeca and Stock in Germany differ from the
Steriflow in that they offer heating by direct steam injection into the water, or by plate
heat exchanger as a customer option. Cooling is by addition of cooling water to the retort
or by indirect cooling through a heat exchanger. A method of recovering process water
may be provided if cooling water is added to the retort.

The FMC Universal and Convenience Food sterilizers differ from the other cascading
water retorts in that they utilize a weir arrangement (a small dam used to direct water
flow) in the container basket to force the heated water to flow over the containers in a
uniform manner from top to bottom or from one side to the other depending upon the
container type. The water then overflows the basket and falls back into the bottom of the
retort where it is picked up by a circulation pump and recirculated through a steam
injector to reheat the water.

When any of these systems are encountered, it is important to determine if the retort
system is being operated under the same conditions used during temperature distribution
testing. The areas of concern for these systems are similar to those for the Steriflow
including the control probe location.

SPRAY WATER RETORT SYSTEMS

Equipment and procedures for processing in spray water retorts are covered by 9 CFR
431.6(c)(1)(2) of the LACF regulations.

Spray Water retort systems are known to be manufactured by the Food Processing
Machinery Division of FMC U.S.A. (FMC Surdry), Surdry S.L. in Spain (Surdry
Convac) and in Japan by Hisaka Works Inc. The Hisaka retort is sold in the U.S. by
Advanced Retort Systems, Inc.

32
 Figure 14

Spray water retort systems may be either static or rotary batch, (end-over-end) systems,
depending upon the make or model (Figure 14 and 15). These retorts are designed to
process a wide variety of packages including: glass, metal, rigid plastic and flexible
pouches. They are normally operated with a compressed air over-pressure to maintain
container integrity during thermal processing.

Spray water retorts differ from the cascading water retort (in which the water falls or is
sprayed over the top of the containers) in that the water is sprayed over the containers,
from several different angles to atomize the air used for over-pressure.

In the Surdry retort the spray nozzles are located on four to six manifolds on the top and
along the sides of the retort. A small amount of water in the bottom of the retort is heated
by the addition of steam through two steam spreaders located in the bottom of the retort.
The water is pumped through the system by a high capacity pump. The water sprays
circulate the steam/air mixture in the retort. The containers are cooled after processing by
the addition of cooling water to the retort. Instrumentation is normally located in the shell
of the retort. The MIG thermometer and the temperature recorder probe are located to
sense the temperature of the steam/air/water mixture in the retort.

33
 Figure 15

In the Hisaka retort, spray nozzles are located on manifolds along the sides and in the top
of the retort. The spray nozzle banks in these retorts can oscillate (back and forward and
up and down). The water in the retort is heated by means of a heat exchanger using
steam. When the thermal process has been completed the water and condensate in the
retort is cooled by the external heat exchanger to cool the product.

The areas of concern with spray water retort systems are similar to those for the water
cascade type retort system.

1. The process must be designed to provide for adequate temperature distribution.

The cold spot in the retort must be determined. This may vary with container type
and arrangement in the retort. Temperature distribution studies should be
performed on each retort model, each product produced, each container type used,
each crate or racking configuration used and on each individual retort installation.

2. Care should be taken to determine the location of the control and recording
instruments. The recording sensing probe must be located where it will provide an
accurate record of the thermal process. The MIG thermometer must be installed
where it will indicate the true thermal processing temperature in the retort.

3. Water flow may not normally be directly controlled as a critical factor. A water

34
 flow measuring device is recommended to provide a more accurate measurement
of actual water flow in the system. Water flow in the system must be the same as
that used during temperature distribution studies in the retort.

4. The holes in the water distribution sprays may become plugged through clogging
with product, and through the buildup of mineral deposits. There should be a
program in place for routine maintenance and cleaning of the water sprays and
water filter screens if present. During the inspection of these systems the water
distribution sprays should be examined to determine if the holes are plugged or
have been reduced by mineral scale buildup.

5. The records maintained by the firm must document that operating steps set-up to
provide uniform temperature distribution in the retort during processing are being
met.

When spray water retort systems are encountered, it is important to determine if the retort
system is being operated under the same conditions used during temperature distribution
testing.

STEAM-AIR RETORTS

Equipment and procedures for processing in steam-air retorts are covered by 9 CFR
431.6(d) of the LACF regulations.

Steam-air retorts are normally batch type static or rotary, end-over-end, retorts. Steam-air
has been used as the heating medium in the Hydrolock (a horizontal continuous feed
water lock retort) manufactured by the Rexham Corporation, and in at least one
hydrostatic retort in Japan. These retorts are however the exception and not the rule.

Known manufacturers of batch type steam retorts include: J.L. LaGarde in France
(Distributed in the U.S. by Stork Food Machinery), Lubeca in West Germany, Marrodan
in Spain, and Barriquand in France (Steristeam). At one time the Container Machinery
Corp. built the Truxton Steristar in the U.S. The Steristar steam-air retort is now built by
Malo. Custom installations of steam-air retorts have been reported and other
manufacturers may exist. An example of the steam-air retort system is the LaGarde
steam-air retort (Figure 16).

The steam-air retort uses a mixture of steam and air, which is added to create an over-
pressure in the retort. The air overpressure allows thermal processing of a wide variety of
containers including: glass, metal cans, rigid plastic, and flexible pouches. Steam-air
mixtures, although in a gaseous state similar to 100% steam, when used as a heating
medium behave more like water. The heat capacity of the steam-air is very small when
compared to pure steam. As the steam condenses and gives off heat, the air remains.
Because the retort uses air in the steam mixture, there must be a method of mixing the air
and steam to prevent the formation of air pockets in the retort and to provide for the rapid

35
movement of the heating medium over the container surface. Air may provide insulation
around the container preventing the heat from reaching the container walls in an efficient
manner. A large fan is normally used to rapidly mix the steam-air mixture and to force
this mixture to flow through the retort and containers during processing.

Figure 16

It is very important to maintain the correct steam-air ratio in this type of retort. The
steam-air ratio should be the same as that used during studies to determine temperature
distribution in the retort.

Steam-air retorts are normally operated at steam-air ratios ranging from 75% steam/25%
air to 95% steam/5% air, depending upon the air over-pressure in the retort. The steam-air
ratio is normally determined by the processing temperature and the type of package being
processed.

The pressure in a steam-air retort must be maintained at the correct pressure to prevent
container distortion and to maintain the correct steam-air ratio. If the amount of steam in
the steam air ratio drops to too low a level, the energy available to heat the product is
reduced. If the temperature is maintained by the steam controller, the partial pressure of
the steam remains constant throughout the process. The pressure of the system is
controlled by releasing over-pressure through a small purge valve and adding compressed
air as needed.

The percent steam can be calculated using the following formula:

36
Steam pressure PSIA (pounds per square inch actual) = % steam Total system pressure
psia

Steam pressure PSIA is determined by determining the amount of steam pressure

generated at a certain temperature [e.g. 240° F generates 10 PSIG (pounds per sq. inch
gauge)] plus 14.7 PSI (atmospheric pressure at sea level) equals 24.7 PSIA. The total
system pressure is determined by taking the gauge reading and adding 14.7 PSI. A steam
air system having a total gauge pressure of 15 lbs operating at 240° F would have 83%
steam and 17% air mixture.

14.7 PSI atmospheric + 10 PSIG (steam at 240°F) = 24.7 PSIA

15 PSIG + 14.7 PSI atmospheric = 29.7
24.7/29.7=83% steam and 17% air

The LaGarde retort is offered in static or rotational end over end agitation models. The
LaGarde is normally operated in the following manner:

- Product is placed into the retort in either standard rectangular baskets or crates for
metal, glass and rigid plastic containers. Special racking trays are used for flexible
and other containers needing support during processing.

- The retort is purged for 1 to 2 minutes through a large purge (vent) valve, the
bottom drain or by vacuum to remove excess air from the retort and to enhance
the steam entry into the retort. Steam is introduced into the retort through steam
spreaders in the bottom of the retort.

- The fan is turned on to circulate the steam-air mixture. The retort is brought up to
temperature during a 3-10 minute come-up period. The maximum amount of
steam is injected at this time. The retort may use a steam bypass valve to provide
a large flow of steam to the retort.

- A process hold period during which the retort temperature is maintained at the
correct temperature by the addition of steam through an automatic steam control
valve. This may be a small steam supply valve used to maintain a more uniform
temperature. Excess pressure is released through a small purge (vent) valve in the
retort shell. Compressed air may be added to the rear of the retort to maintain the
retort over-pressure.

- Pre-cool, at the end of the thermal process a small amount of water may be
injected into the retort steam-air channels to condense the steam or in some
models cold water coils located in the retort are used to condense the steam.

- Cooling is then completed by adding water to the retort through top or bottom
water spreaders. In some of the newer systems plate heat exchangers may be used
to cool products through indirect cooling.

37
The steam-air mixture is forced through the LaGarde retort by a fixed speed fan located
at one end of the retort. The steam-air mixture is normally drawn through the basket by
the fan (an automotive type blade fan in the LaGarde and a squirrel cage type in some
other systems) and pushed back up along the sides of the retort through channels created
by welding metal sheets to the top and bottom at each side of the retort. The plates are
generally referred to as "directional baffles". The space between the plates and the retort
shell is sometimes referred to as the steam-air "plenum". The flow rate is fixed at
approximately 30 cubic feet per second. LaGarde states that a temperature overshoot,
(where the temperature of the retort is operated at several degrees above the required
product temperature for the first part of the process and as the internal package
temperature begins to achieve the desired temperature the temperature of the retort is
reduced) can be used to produce a superior product. This process is reportedly designed
to achieve shorter processing times and better heat transfer without stressing the container
by causing high pressure within the containers. If the temperature overshoot is used, it
must be filed as part of the process schedule.

The Lubeca LW3003 steam-air retort is offered in both static and rotational models. The
Lubeca differs from the LaGarde in that in addition to using a large fan to mix the steam-
air mixture this system also pumps the condensate from the bottom of the retort and
distributes the condensate over the top of the containers. At the beginning of the process,
a small amount of water is added to the bottom of the retort. This water is heated by the
addition of steam through steam spreaders in the bottom of the retort. A large squirrel
type ventilator fan pulls air along the bottom of the retort and pushes the air along the top
of the retort and back through the crates of product. Instrumentation is located in the shell
of the retort. The temperature of the condensate and water may not be measured or
recorded during production. Following the thermal process the containers are cooled by
the addition of cooling water to the retort.

The Barriquand Steristeam retort differs from the LaGarde in that each basket has it own
circulation fan. The fans are mounted on the side of the retort and circulate the steam-air
mixture up over the basket and back through the containers. Cooling of product is
normally through an external heat exchanger or by the addition of cooling water to the
retort shell at the customer’s option.

The Truxton Steristar is a modified version of the LaGarde. The Steristar may use a
squirrel cage or an automatic type fan, heavier components, proportional control valves,
preheated compressed air and a number of other modifications to the LaGarde system.
Operation of the system is similar to the LaGarde.

Air flow in the steam-air retort system is very important to the maintenance of proper
temperature distribution during processing. Changes in the container, crate or loading
configuration can change the air flow in the retort. Steam-air retorts are normally
operated with a full load of product or with dummy crates of product to fill out the retort
during the processing of partial loads. In some systems, a baffle may be used to block off
the retort at the last crate and allow for processing with less than a full retort load.

38
Temperature distribution studies or other documentation should be on hand to
demonstrate that adequate temperature distribution is achieved under less than full load
conditions and with the container/crate configuration being used.

There should be some method for determining that the fan in a steam-air retort is
operating. A visual inspection of the fan operation should be made on a routine basis.
Inspection of operation of the fan should be documented.

DURING THE INSPECTION OF ALL THERMAL PROCESSING SYSTEMS, BE

CERTAIN TO REFER TO THE APPLICABLE SECTIONS OF THE MEAT AND
POULTRY CANNING REGULATIONS.

39
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Institute For Thermal Processing Specialists

GUIDELINES FOR CONDUCTING THERMAL PROCESSING STUDIES 
The following recommendations are to be considered voluntary guidelines.  These recommendations 
do not preclude the application of other methods and equipment for conducting thermal processing 
studies.  These guidelines have been developed by consensus of the Institute for Thermal Processing 
Specialists and should be given serious consideration for adoption as methodology by individuals 
performing thermal processing studies. 

The Institute for Thermal Processing Specialists is a non‐profit organization established exclusively for 
the purpose of fostering education and training for those persons interested in procedures, techniques 
and regulatory requirements for thermal processing of all types of food or other materials, and for the 
communication of information among its members and other organizations. 

This document is a compilation and re‐structuring of previously published IFTPS guidance documents.  
Prior documents were modified to follow a common format and were also updated to reflect current 
practices.  Common sections amongst previously published documents, such as Retort Survey, were 
placed into separate chapters.  Information was added to Chapters on Temperature Distribution, Heat 
Transfer Distribution, and Heat Penetration to provide recommendations regarding Data Analyses, 
Success Criteria, and Risks, Issues and Other Considerations. 

Hyperlinks have been embedded throughout the document to assist the reader in navigating between 
different chapters.  Hyperlinks may be identified as underlined, blue text. 

Instructions for following hyperlinks in documents 
To follow a link to the point being referenced – Press CTRL key + left click on the mouse to move to 
referenced item.  Note that the instruction to CTRL + click will also show when the cursor is placed 
within a hyperlink. 

To return to the place in the document where you were reading – Press ALT key + back arrow(Alt + ←) 
(note that using the “backspace” key will not work). 

   
Issue Date: March 13, 2014 
Supersedes Date:  New    i 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

This document was approved for publication in March, 2014 by the IFTPS Board of
Directors.

Institute For Thermal Processing Specialists

304 Stone Rd. W., Ste. 301, Guelph. ON N1G 4W4
P: 519 824 6774 F: 519 824 6642 info@iftps.org
www.iftps.org

   

Issue Date: March 13, 2014 
Supersedes Date:  New    ii 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

TABLE OF CONTENTS

Chapter 1 – Definitions

Chapter 2 – Test Equipment and Standardization/Calibration

Chapter 3 – Documenting Processing Equipment and Test Conditions

Chapter 4 – Conducting Temperature Distribution Studies

Chapter 5 – Conducting Heat Transfer Distribution Studies

Chapter 6 – Conducting Heat Penetration Studies

Appendices –
A. Literature Cited 
B. Documenting Processing Equipment and Test Conditions
C. Temperature Distribution – Data Monitoring/Collection Points by Retort Type
D. Heat Penetration Documentation Checklist
 

   

Issue Date: March 13, 2014 
Supersedes Date:  New    iii 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

1 DEFINITIONS 
This chapter provides definitions commonly used for thermal processing studies. 

TERM  DEFINITION 
These are containers used to fill the retort during thermal processing studies to 
simulate production conditions.  Typically, ballast containers for heat penetration, 
temperature distribution and heat transfer distribution studies are the same type, 
shape and size of containers as used for the intended process.  In some retort 
Ballast Containers  systems, e.g., multi‐basket batch retorts, ballast containers may not need to be the 
same in baskets not containing heat penetration and heat transfer distribution 
probes.  Material used for filling containers may be the test product, or any suitable 
material having heating characteristics similar to that of the test product, or in some 
circumstances, water (e.g., temperature distribution). 
Heat transfer characteristic of some foods, particularly those with starches, where 
the heat transfer rate changes due to a change in the product as a result of product 
Broken Heating 
heating.  The change in heat transfer rate may represent a change from heating 
primarily by convection to heating by conduction. 

To check, adjust, or determine by comparison with a traceable standard the 
Calibration 
graduations of a quantitative measuring instrument. 

A means by which filled packages are held/carried in a retort.  Cassettes/trays/racks 
Cassettes/Trays/Racks  may be loaded into cubes, baskets, or other means to convey filled packages into 
and out of a retort. 
The cold spot for heat penetration studies is determined experimentally and 
represents the slowest heating location within the container.  In the case of non‐
Cold Spot – Heat Penetration 
homogenous foods, the slowest heating food particle in the slowest heating location 
within the container would be considered to be the cold spot. 
The cold‐spot for temperature distribution is generally that area of the retort which 
Cold Spot – Temperature 
is the last area in the retort to reach a minimum processing temperature during 
Distribution 
come‐up. 
The slow/slower to heat location(s) for Heat Transfer Distribution is generally the 
Cold Spot – Heat Transfer 
location(s) in the retort where heat transfer into the product is the slowest.  This is 
Distribution 
indicated by the location with the largest fh value. 
Come‐up time (CUT) is defined as the time requirement for the reference TID to read 
Come‐Up Time (CUT)  at or above the minimum process temperature AND all TMDs to read within 1F° 
(0.5°C) of minimum process temperature within 1 minute of starting the hold time.  
Commercial sterility is defined as the condition achieved by application of heat, or 
other treatments that renders the product free of viable microorganisms having 
Commercial Sterility  public health significance as well as microorganisms of non‐health significance 
capable of reproducing in food under normal non‐refrigerated conditions of storage 
and distribution. 

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐1 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Computer used for automation of electromechanical processes.  Also referred to as a 
Computer Control System 
Programmable Logic Controller (PLC). 

A type of heat transfer that may be characterized as one where agitation of the 
Conduction 
package with the food does not impact the heat transfer rate. 

A type of heat transfer that may be characterized as one where agitation of the 
Convection 
package with the food does impact (positively) the heat transfer rate. 
A non‐agitating (i.e., still) batch retort wherein cans are sterilized in saturated steam 
as a “jumble pack”, without baskets, trays or cassettes. Loading is by dropping cans 
Crateless Retort 
from the retort top into a cushion of water and cans are unloaded by gravity 
dropping out the bottom into a water canal with a drag chain to drying and packing. 
US‐FDA 21CFR Part 113 defines critical factors as – “any property, characteristic, 
condition, aspect, or other parameter, variation of which may affect the scheduled 
Critical Factors  process and the attainment of commercial sterility”.  Critical factors may include 
physical and chemical aspects/parameters associated with the container, the 
product, the retort and processing conditions. 

The time for the heat penetration curve to traverse one log cycle. Also referred to as 
fh 
the heating rate index. 

Fill Weight means the weight of solid product in the container before processing and 
does not include the weight of the package or cover liquid (if applicable); Drained 
Fill, Drained, and Net 
Weight is the weight of solids after processing; and Net Weight of a product refers to 
Weights 
the weight of all product in the container including any cover liquid minus the weight 
of the container. 
Flow Meter  An instrument/device/sensor that measures fluid flow rate. 
Studies conducted to determine and establish a Scheduled Process.  Heat 
Heat Penetration  Penetration studies are typically conducted under “worst case” conditions for 
product, package, location, and retort parameters. 
Heat transfer distribution studies are used to establish the ability of a retort process 
Heat Transfer Distribution  to uniformly mix and distribute the heat transfer medium especially when the heat 
transfer into product may be rate limiting. 
Appropriate material such as a polymer, clay, or food product with 
Heat Input Unit(HIU)  repeatable/definitive thermo‐physical properties, and capable of being used for heat 
transfer distribution studies. 
Plot of the logarithmic difference between either retort temperature and product 
Heat Penetration Curve  temperature (heating curve) or product temperature and cooling medium 
temperature (cooling curve) versus time. 
The condition which excludes the ingress of microorganisms, filth or other 
Hermetic Seal  environmental contaminants that could render the product unfit for consumption or 
which could reduce the quality of the product to a level less than intended. 

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐2 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

The average temperature of the contents of the coldest container to be processed at 
Initial Temperature 
the time the sterilization cycle begins. 
Any food, other than alcoholic beverages, with a pH >4.6 and a water activity (aw) 
Low‐Acid Canned Food 
greater than 0.85 packaged in a hermetically sealed containers that are thermally 
(LACF) 
processed and stored at ambient temperatures. 
A depiction showing locations of probes and/or probed containers (e.g., temperature 
Loading Pattern/Map 
distribution, heat penetration, and heat transfer distribution) within a retort load. 
Condition that occurs when more than one container is stacked fully or partially on 
Nesting/Shingling  top of another container.  In the case of pouches, this is referred to as shingling.  
Nesting/shingling may negatively impact heat transfer/heat penetration. 
Pressure in excess of that corresponding to saturated steam vapor pressure at a 
Overpressure  given temperature and when corrected for altitude.  Overpressure may be necessary 
to maintain package integrity during the process. 
Soft rubber or other material that is used to create a tight seal around TMDs/PMDs 
Packing Gland (Stuffing Box)  that assists in providing a means to penetrate the retort shell without allowing 
process media to leak to atmosphere (if applicable). 
A measure of acidity or alkalinity.  Chemically, pH is defined as the negative log of 
pH 
the hydrogen ion concentration. 

Piping and Instrumentation  Diagram which shows the piping of the process flow together with the installed 
Diagram (P&ID)  equipment and instrumentation. 
In a steam/air retort, the plenum/shroud is the space between the retort shell and 
the portion of the retort holding the baskets/cassettes.  The function of the 
Plenum/Shroud 
plenum/shroud, usually in conjunction with a fan, facilitates movement of steam/air 
through the retort and retort load. 

Pocket space  Space within a cassette/rack/tray to hold a package. 

Pressure Control Sensing 
Instrument used to control pressure inside the retort. 
Device 
Pressure Indicating Device  Instrument used to monitor pressure inside the retort, e.g., pressure gauge or 
(PID)  pressure transmitter with electronic display. 
Pressure Measuring Device  Pressure sensor placed within (or mounted on) the retort to accurately monitor 
(PMD)  pressures attained and maintained throughout the applied process. 
A change in any critical factor of the scheduled process that reduces the sterilizing 
Process Deviation  value of the process, or which raises a question regarding the public health safety 
and/or commercial sterility of the product lot/batch. 
Scientific procedure to determine the adequate process time and temperatures 
Process Establishment 
required to produce commercially sterile canned products. 
Resistance Temperature  Thermometry system based on the positive change in the resistance of a metal 
Detector(RTD)  sensing element (commonly platinum) with increasing temperature. 

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐3 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Any closed vessel or other equipment used for thermal processing.  May also refer to 
the act of applying a thermal process to a canned food in a closed pressurized vessel.  
Retort 
May also be referred to as a “sterilizer”.  The terms “retort” and “sterilizer” are often 
used interchangeably. 
In Continuous Rotary/Reel and Spiral Cooker Cooler retorts, cans enter and exit the 
processing vessel through mechanical pressure locks. Once in the vessel, cans move 
Retort – Continuous  through a spiral track mounted on a reel that is rotating inside a horizontal 
Rotary/Reel and Spiral  cylindrical shell. In one revolution of the reel, cans roll by gravity along the bottom 
Cooker/Cooler Retorts  part of the arc (approximately 90‐120°), which provides most of the product mixing 
within the can. The cans are essentially static as they pass through the remainder of 
the arc (approximately 240‐270°). 
A retort in which total pressure in the sterilization section is determined and 
Retort –Hydrostatic  maintained by the hydrostatic pressure of inlet and outlet water columns.  Packages 
are continuously conveyed through the machine. 
Separator/divider sheets are used to separate layers of packages in a basket/crate.  
These typically contain perforations/holes to help facilitate free movement of the 
Separator/Divider Sheet 
heat transfer medium.  Materials of construction can vary – metal/stainless steel, 
rubber, plastic, and so forth. 
The process defined by the processor as adequate under the conditions of 
Scheduled Process 
manufacture for a given product to achieve commercial sterility. 
Should is used in this document to indicate a recommendation or option for 
Should 
consideration. 
Heat transfer characteristic of some foods where the heat transfer rate is relatively 
Simple Heating 
constant during product heating.  
A device that allows for transfer of the thermocouple voltage signal from a rotating 
Slip Ring 
environment to a stationary electrical contact outside of a retort. 
Indicator located in the retort shell to determine the direction and to measure flow 
Steam/Air Flow Indicator 
(cubic feet per minute ‐ cfm) of process media. 
The steam/air ratio (for isothermal/isobaric conditions of the cook segment) is 
calculated by volume by determining the amount of steam pressure at a certain 
temperature plus the atmospheric pressure at sea level and dividing that value by 
the total absolute Total Pressure of Steam and Air/Nitrogen as indicated by the 
retort gauge pressure plus the atmospheric pressure.  For example, using the steam 
tables, at 240°F (115.6°C), the absolute saturated steam pressure at sea level is 
Steam/Air Ratio  24.968 psia/1.722 bar (or 10.272 psig and 0.708 bar gauge).  For a process with a 
gauge pressure of 15psig (1.034 bar gauge), the absolute pressure at sea level is 
29.696 psia (2.048 bar).  This would equate to a steam/air mixture that is 84% 
saturated steam (i.e., 24.968/29.696 X 100% or 1.722/2.048 X 100%) and 16% 
overpressure air (i.e. 29.696‐24.968/29.696 X 100%).  Note that the altitude of the 
processing facility should be considered when converting gauge pressure to absolute 
pressure. 
Steam/Air Retort  A steam/air retort is a batch retort that uses air/nitrogen to provide overpressure. 

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐4 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

In a forced‐flow retort, a mixing fan induces a forced convection of the process 
Steam/Air Retort – Forced  heating media by drawing the steam/air mixture through the product and circulating 
Flow Steam/Air Retort  it through a return plenum.  Steam is introduced between baskets while air over‐
pressure is introduced into the return plenum cavity. 
In this type of retort, small vent valves on the retort remain open after desired 
temperature and pressure are achieved and provide continuous venting of the retort 
Steam/Air Retort – Air 
during the heating period.  Air is re‐introduced into the retort as needed to satisfy 
Make‐up Steam/Air Retort 
over‐pressure requirements while steam is simultaneously added to maintain 
temperature. 
In this type of retort, a continuous flow of steam and air are passed through the 
Steam/Air Retort – Positive   vessel to create a homogeneous mixture throughout the retort.  This creates an 
Flow Steam/Air Retort  overpressure condition in the retort and results in continuous venting of the 
steam/air mixture thus creating flow past the containers. 

Sterilizer  See definition above for Retort. 

As used in this document, sufficient sampling frequency is determined by the 
Sufficient Sampling 
processor and should be frequent enough to confirm that the measured parameter 
Frequency (Data Collection) 
is within control. 

Temperature Control 
Device used for controlling temperature in a retort. 
Sensing Device 

Device used for monitoring temperature, including thermometers, thermocouples, 
Temperature Indicating  RTDs and thermistors and generally referred to as the “official” or “reference” 
Device(TID)  temperature monitoring device on a retort system.  A Mercury‐in‐Glass (MIG) 
thermometer is an example of a TID. 
Temperature Measuring  Device used for measuring temperature, including thermometers, thermocouples, 
Device (TMD)  RTDs, wireless data‐loggers, and thermistors. 

Temperature Uniformity and  Verification of temperature across/within the retort load (uniformity) and over time 
Stability  (stability) of the process particularly during Cook/Hold. 

TMD manufactured from semiconductor materials which exhibits large changes in 
resistance proportional to small changes in temperature. Thermistors are more 
Thermistor 
sensitive to temperature changes than thermocouples or RTDs and are capable of 
detecting relatively small changes in temperature. 
TMD composed of two dissimilar metals which are joined together to form two 
junctions. When one junction is kept at an elevated temperature as compared to the 
Thermocouple 
other, a small thermoelectric voltage or electromotive force (emf) is generated 
which is proportional to the difference in temperature between the two junctions. 

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐5 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Studies conducted in a sterilizer (retort)using distributed temperature measuring 
devices (TMD) to establish venting procedures, venting schedules, come‐up 
requirements, and temperature stability and uniformity, which are necessary to 
Temperature Distribution 
establish heating and cooling performance (i.e., temperature uniformity) throughout 
the retort.  Temperature distribution studies are typically performed using actual 
production retort conditions or parameters. 

Tray/Rack  See Cassette/Tray/Rack above 

There are multiple definitions of the word “validation”.  In the context of this 
Validation  guideline document, validation is assumed to mean at least two successive and 
successful replicate studies that meet established success/acceptance criteria. 
A vent is a device/valve through which air is removed from a retort.  Venting is the 
Vent/Venting 
process by which air is removed. 
In the context of this guidance document, verification is assumed to mean replicate 
studies that are intended to confirm a process.  Verification may also be used to 
Verification 
indicate confirmation of the calibration status of process measurement devices used 
to collect thermal process data. 
Water activity (aw) is defined as the ratio of the partial pressure of water above a 
Water Activity (aw) 
food to the water vapor pressure of pure water at a given temperature (aw= p/po). 
A water cascade retort is defined as one where a small amount of process water is 
drawn from the bottom of the retort by a high‐capacity pump and distributed 
through metal plate(s) or manifold(s) in the top of the retort.  This process water 
cascades down over the retort cassettes, cages or racks in a rainwater or “shower” 
Water Cascade Retort  fashion, passing over the product containers on the way back to the bottom of the 
retort where it is re‐circulated through the heating and distribution system.  
Processing water may be heated using one or more direct or indirect heating 
methods including heat exchangers, direct steam injection, or via steam distribution 
pipes or spreaders. 
A water immersion retort is defined as one where process water is sometimes 
heated in a separate vessel and once the process water reaches the desired 
processing temperature, is dropped into the processing vessel.  Water is re‐
Water Immersion Retort 
circulated during processing.  Sufficient water to completely cover the packages may 
be used.  In other cases, packages may only be partially covered with water during 
processing. 
A water spray retort is defined as one where a controlled amount of process water is 
drawn from the bottom of the retort by a high capacity pump and distributed 
through spray nozzles located along the top and sides of the retort.  This process 
water is sprayed over the retort cassettes, cages or racks in a high‐pressure “mist” 
Water Spray Retort  fashion passing over the product containers on the way back to the bottom of the 
retort where it is re‐circulated through the heating and distribution system.  
Processing water may be heated using one or more direct or indirect heating 
methods including heat exchangers, direct steam injection, or steam distribution 
pipes or spreaders. 
  A sensor/measuring device that is self‐contained (i.e., does not require wires).  These 

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐6 
 
 IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Wireless Data‐logger  devices typically require programming prior to use and collected data are then 
downloaded or transmitted for analyses after use. 
The coefficient of variance is mathematically calculated by dividing the standard 
%CV  deviation of a set of numbers by the average of the same set of numbers and then 
multiplying that quotient by 100.  (%CV = standard deviation/average * 100) 
 

   

Issue Date: March 13, 2014 
Supersedes Date:  New     1‐7 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

2 TEST EQUIPMENT AND CALIBRATION OF TEST EQUIPMENT 
SCOPE 

2.1. The guidelines in this chapter apply to equipment used to collect thermal process data in any 
retort system.  The guidelines apply to both internal and external measuring and data collection 
systems.   Test equipment used for collecting thermal process data should be suitable for the 
purpose of the studies being conducted.  Devices to collect temperature distribution, heat 
transfer distribution, and heat penetration data, in general, should be calibrated relative to the 
expected test conditions and ranges prior to conducting thermal process studies.  Ideally, 
devices should also be calibrated upon completion of thermal process studies.  Process efficacy 
and success criteria of thermal processing studies may not be met if sensors and measuring 
devices are inaccurately calibrated. 
2.2. Biological indicators are not addressed in this chapter.
 
OBJECTIVE 
 
2.3. The objective of this document is to provide guidance with regard to calibration of test 
equipment used to collect thermal process data. 
 
TOOLS, EQUIPMENT, INSTRUMENTATION 
 
2.4. Data Acquisition System – The data acquisition system should be calibrated prior to use.  It 
should also be equipped with sufficient channels to accurately monitor and record 
temperature/pressure within the process delivery system.  Manual recording of data may be 
used if a sufficient sampling frequency can be maintained. 
2.5. Temperature Measuring Device (TMD) – TMDs may be thermocouples, wireless data‐loggers, or 
other similar devices.  All TMDs must be of sufficient accuracy, size, and length, and in sufficient 
quantity, to adequately and accurately monitor the process environment. 
2.6. Pressure Indicating Devices – Operational gauges, electronic indicators, and/or wireless data‐
loggers may be used to monitor pressures associated with the retort operation during a test.  
These devices should be calibrated prior to the start of data collection.  Typical pressure 
measurements could include: retort vessel pressure, steam line pressure, and other line 
pressures that may be critical to the process. 
2.7. Reference Temperature Indicating Device (TID) – This may be a retort Mercury‐In‐Glass (MIG) 
thermometer or other valid reference temperature measuring device including a digital 
thermometer of sufficient accuracy and precision. 
2.8. Packing Gland (Stuffing Box) – This is needed for entry of lead wires into the retort when wired 
data collection devices are used.  Materials used should be soft enough to provide a tight seal 
without over‐tightening and damaging the TMDs.  Examples include Neoprene or other 
synthetic materials. 
Issue Date: March 13, 2014 
Supersedes Date:  New     2‐1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

2.9. Slip Ring – This allows for transfer of thermocouple outputs from a rotating environment to a 
stationary electrical contact outside of the retort. 
2.10. Flow Meters – Where applicable, flow meters may be used to measure flow of process water 
during come‐up, heating, and cooling in those systems using circulating pumps.  Flow meters 
may be used to measure volume or velocity of air flow in those systems using air for agitation 
of heating and cooling media. 
2.11. Stopwatch – This is needed to verify rotation rate/speed in systems that have agitation and/or 
continuous container handling. 
2.12. Heat Input Unit (HIU) – An appropriate material to simulate the product being studied in heat 
transfer distribution studies.  Packaged product may also be used as an HIU.

METHODS FOR TEST EQUIPMENT STANDARDIZATION 
 
2.13. Retort Temperature Indicating Device (TID) – The reference temperature measurement device 
must conform to applicable regulations.  For example, US‐FDA regulation 21 CFR Part 113 
establishes the requirement that temperature indicating devices and reference devices must be 
tested against a reference device for which the accuracy is traceable to a National Institute of 
Standards and Technology (NIST), or other metrology institute.  The reference device is typically 
calibrated for accuracy against a known certified reference device at least annually.  The 
preference is to have the Retort TID calibrated near to the time data are collected.  The last 
calibration check date should be included in the study documentation. 
2.14. Measurement System(s) – Measurement systems include as applicable: thermocouples/TMDs 
(with extension wires as applicable), data acquisition system, pressure measurement devices, 
and flow meters. The recommendations of the datalogging equipment manufacturer should be 
followed or an instrument professional should be consulted regarding the correct grounding 
technique to use. 
 
TMD Standardization/Calibration 
2.14.1.Prior to conducting thermal process studies, standardization or calibration of test 
equipment should be performed.  Thermocouples ideally would be calibrated in the test 
retort(s).  All thermocouples, extensions, connections and the specific data logger should 
be assembled as they will be used under the actual test conditions. Consideration for 
conducting duplicate calibration studies prior to conducting critical thermal processing 
studies is recommended. 
2.14.2.An acceptable method of calibration is to bundle all TMDs and locate them in close 
proximity to the known accurate reference TID, taking care not to inhibit flow of the heat 
transfer medium across the reference TID.  The retort is brought up to the same 
sterilization set‐point temperature and pressure as defined for the test and the retort is 
allowed to equilibrate.  Equilibration time may be dependent upon the specific retort 
and/or retort type.  The temperature differences between the reference TID and TMDs are 
then calculated and documented.  These differences may be applied as correction factors 
for each TMD.  A typical range of correction factors for thermocouples is usually not more 
Issue Date: March 13, 2014 
Supersedes Date:  New     2‐2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

than 1‐2F° (0.6 – 1.2C°).  Large correction factors may indicate an issue with the TMD that 
merits investigation and corrective actions prior to use in thermal processing studies.   
Non‐thermocouple TMDs such as wireless data‐loggers should be within manufacturer’s 
specifications at the time of their use provided those specifications are consistent with 
conditions of intended use of the TMD.  
2.14.3.Alternatively, TMDs may be calibrated off‐line in an established calibration program 
within the temperature range to be used during data collection.  The difference between 
the TMDs against the known accurate reference device should be calculated and 
documented as part of the study data.  This difference may be applied as correction 
factors for each TMD. 
2.14.4.Verification of the calibration of all TMDs after completing thermal processing studies is 
recommended.  Off‐sets which are substantially different than the pre‐study values should 
be evaluated relative to the data that were collected. 
 
Pressure Measurement Devices – Various methods are available to calibrate pressure 
measurement devices.  Traditional calibrated and traceable dead weight testers (or their 
electronic analogs) are recommended to be used as the primary reference standard against 
which pressure gauges, transmitters and data logging devices should be calibrated.  
Regardless of method used, standardization results should be documented as part of the 
overall study data package where pressure is part of the process.  Accuracy of pressure 
measurement systems should preferably be ≤1% of the calibrated and traceable pressure 
reference standards used, in the planned working or operating pressure range of the 
processes in which they are to be used.  In addition, the accuracy should satisfy the 
applicable following considerations: 
2.14.5.For steam/air retort processes, the accuracy of pressure measurements should not result 
in calculated intrinsic (unsafe) Steam Air Ratios ≥1% (i.e. richer in steam) for the actual 
process value. 
2.14.6.For non‐overpressure retort systems (primarily saturated steam), the accuracy of 
pressure measurements should not result in an overestimate (unsafe) error of the 
equivalent saturated steam temperature (corrected for sea level) of ≥0.2Fo (0.1Co), if 
process temperatures are planned to be calculated from pressure values for any 
evaluation or consideration. 
 
Flow Meters – A number of methods may be used to calibrate flow meters.  Regardless of 
method used, standardization results should be documented as part of the overall study 
data package.   
2.14.7.Fluid flow rates are often determined by flow meters or indirectly by revolutions per 
minutes (RPM) of fans, pumps or motors for known/fixed cross section flow areas. 
2.14.8.Flow meters (usually mechanical or electronic), direct contact or non‐contact, have 
become increasingly specialized and complicated and manufacturers have set up 
specialized flow test benches to provide calibration services for their flow meters. 
Issue Date: March 13, 2014 
Supersedes Date:  New     2‐3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

2.14.9.Periodically (e.g., annually), factory electronic flow sensor output should be verified with 
volumetric, gravimetric or other approaches (e.g., tachometers, velocity meters, current or 
voltage draw) and results compared to calibration data.  Re‐calibration would be needed if 
the verification results are not consistent with the calibration data.   
2.14.10.Based on the way flow is measured or imputed, process fluid flow sensor accuracy 
should be calibrated for use in production or validation in the operating range of the 
process and validations should factor in known off‐sets, errors and calibration 
inaccuracies.  Process efficacy and success criteria of thermal processing studies may not 
be met if flow meters are inaccurately calibrated. 
 
Stopwatches – Stopwatches typically are received calibrated with an expiration date from the 
stopwatch equipment supplier. 
 
Non‐product based Heat Input Units (HIU) – Each HIU used in heat transfer distribution studies 
must have a unique identity. 
2.14.11.Using either a pilot scale retort or the test retort, a standardization test for a complete 
set of HIU (e.g., 12‐24 separate units) should be made using expected operating 
parameters (i.e., temperature and pressure) to establish a baseline for the heating 
performance as measured by the heating rate index (i.e., fh) prior to use and periodically 
during their life expectancy.    
2.14.12.All HIUs within a set should be in close proximity to one another during the 
standardization/calibration study. 
2.14.13.All TMDs used in conjunction with HIUs must be calibrated prior to calibrating the HIU. 
2.14.14.A reasonable means of determining acceptable standardization for the use of a set of 
HIUs in heat transfer distribution studies at any time during their life expectancy is to 
utilize the statistical measure of coefficient of variance of the fh of the HIUs (%CV = 
standard deviation/average * 100%).  A value of less than or equal to 1% would be 
acceptable for a set of HIUs to be used to collect heat transfer distribution data. 
2.14.15.In addition, each individual non‐product based HIU within a set should always be within 
1% of its historical performance as measured by fh for the same 
standardization/calibration process.  Once the %CV exceeds 1% for a given HIU relative to 
its established baseline, consideration for removing it from service should be made.  A 
rationale for using an HIU that falls outside of this recommendation could be based on its 
performance in a specific study provided the data collected meet the success criteria 
established (i.e., fh %CV ≤5% in a heat transfer distribution study).  
 
Product‐based HIU – Product should be representative of the product heating type (e.g., 
conduction, convection) to be studied during heat transfer distribution tests. 

Issue Date: March 13, 2014 
Supersedes Date:  New     2‐4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

RISKS, ISSUES, AND OTHER CONSIDERATIONS 

2.15. To meet the calibration criteria noted above (section 2.14) and to ensure accuracy of test 
results, consideration should be given to minimizing errors inherent in any component of the 
temperature measuring system.  For example, use of special limits of error (SLE) wire or 
premium grade thermocouple wire should be used to make thermocouples.  The use of 3 or 4 
wire high accuracy RTD can help to reduce intrinsic error. 
2.16. Thermocouple Calibration: Thermocouples should be calibrated against a traceable calibration 
standard (e.g., thermometer, RTD, thermistor). Inaccuracies in temperature measurements 
may result in errors in thermal process studies; hence, frequent calibration is essential to 
provide reliable data. Factors affecting calibration include: worn or dirty slip‐rings, improper 
junctions, metal oxidation, multiple connectors on one thermocouple and inadequate data 
acquisition system cold junction compensation. As a consequence, thermocouples should be 
calibrated in place as part of the complete data acquisition system.  Some precautions when 
using thermocouple‐based data acquisition systems include: minimizing multiple connections 
on the same wire, cleaning all connections, grounding the thermocouples and recording device, 
slitting thermocouple outer and inner insulation outside the retort to prevent flooding of data‐
logger or data recording device (4, 8), and using properly insulated thermocouple wires. 
2.17. HIU –The considerations discussed below apply to HIUs other than packaged product. 
2.17.1.Inherent variations associated with any HIUs must be considered when selecting the 
specific type of HIU, e.g., polymer‐based solid material, bentonite suspensions, and oils.  In 
addition, the design and geometry of an HIU must also be considered. 
2.17.2.The nature of the process environment (temperature and pressure) may dictate the HIU 
material.  The material selected must withstand the operating conditions repeatedly and 
reliably. 
2.17.3.The geometric design of the HIUs should consider the package(s) general shape in all 
dimensions and placement within the package holding system (e.g., rack, trays, baskets) in 
order to mimic potential flow restrictions of the process media.  Typically, the HIUs should 
be designed to conform to the shape of containers forming the ballast.   
2.17.4.The thermal properties of the HIUs should be verified before and after their last use to 
ensure that their properties remain unchanged.  Since material thermal diffusivity relates 
indirectly to heating rate index (i.e., fh), thermal property verification could be in the form 
of heating rate determination of all HIUs under specific heating conditions before and after 
a test. 
2.17.5.Factors that can influence standardization/calibration of the HIU materials include: 
machining tolerances, seals, air and water residues in the TMD wells, and heat degradation 
of the HIU upon repeated use. 
2.17.6.HIUs such as bentonite suspensions at different concentrations exhibit different heating 
characteristics resulting in convection and conduction (simple or broken heating) profiles.  
Preparation steps should be consistent from batch to batch to minimize inherent errors 
(13, 14). 

Issue Date: March 13, 2014 
Supersedes Date:  New     2‐5 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

2.18. When actual packaged product is being used to collect heat transfer distribution or heat 
penetration data, a critical assumption is that it is uniform across all test packages.  Any 
intrinsic variability in the product would be built into the data collected during its use in specific 
thermal processing studies such as heat penetration or heat transfer distribution tests.  This 
intrinsic variability would/could eventually affect Process Establishment or meeting Heat 
Transfer Distribution Success Criteria. 

DOCUMENTATION 
 
Calibration or standardization results should be included in study documentation.  A listing of records 
required by US‐FDA regarding calibration records for temperature indicating and reference devices can 
be found in 21 CFR Part 113.100. 

   

Issue Date: March 13, 2014 
Supersedes Date:  New     2‐6 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

3 DOCUMENTING PROCESSING EQUIPMENT AND TEST CONDITIONS 

It is important to establish proper documentation regarding the processing equipment used for thermal 
processing studies including:  temperature distribution, heat transfer distribution, and heat penetration.  
While processing equipment surveys are not a part of data collection per se, they are important in 
identifying retorts that are used for thermal processing studies, documenting study test conditions, as 
well as helping plant management realize that projects outside the retort room may have an effect on 
processing operations.  

Surveys should be periodically performed on all retorts to ensure that they remain consistently and 
properly installed to previously documented conditions.  These may also be an important part of a 
plant’s change control program.  Note that USDA requires annual surveys or audits of retort systems. 

SCOPE 

The guidelines in this chapter are applicable to any retort system.  The listed items for a processing room 
survey should not be considered as being “all inclusive”.  Some listed items may not be applicable to the 
particular retort/processing system being documented. 

OBJECTIVES 

The objectives of conducting a retort/processing survey include: 
3.1. Documentation of test retort(s). 
3.2. Providing documentation to aid in the identification and sometimes the selection of retorts for 
temperature distribution, heat transfer distribution, and heat penetration studies. 
3.3. Documentation of “as existing” conditions that may then be used as part of an overall change 
control program. 
 
ITEMS TO INCLUDE IN THE SURVEY 
 
Retort 
3.4. Shell – Physical dimensions of the retort and capacity (e.g., number of baskets, cassettes, 
dividers, etc.).  Secure if possible, the retort manufacturer’s or factory blueprints of the retort 
and all attendant piping, as well as, any alterations since the retort was originally installed. 
3.5. Controls‐ Process controls and installation variations from one retort to another (if any) in the 
selected test retort group 
3.6. Location of Instrumentation including instrument wells – Size, shape and location of well(s) 
used to locate sensors. 
3.7. Reference Temperature Indicating Device (TID) – Type, location and calibration status. 
 

Issue Date: March 13, 2014 
Supersedes Date:  New     3‐1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

 
 
3.7.1.Where used, Mercury‐in‐glass (MIG) thermometer location, temperature range and 
increments, length of scale, calibration date, and length of insertion, i.e., the length of the 
sensing bulb that is inside either the retort shell or instrument well. 
3.7.2.Electronic TID type (e.g., RTD, thermocouple, thermistor, etc.), range, response time, 
location, and length of insertion.  If applicable, record if the reference TID is located 
directly in the heat transfer medium. 
3.8. Temperature Control Sensing Device– Type and location of the temperature control sensing 
device.  Describe location of control sensor in relation to the TID sensor and to the steam 
distributor.  If applicable, record if the temperature control sensor is located directly in the heat 
transfer medium. 
3.9. Pressure Control Sensing Device – Type and location of the pressure control sensing device. 
3.10. Overflow/purge/vents (air removal) 
3.10.1.Valve type and size 
3.10.2.Pipe size and connections to drain headers or channels 
3.10.3.Vents – location and size of pipes, type and size of valves 
3.10.4.Vent manifold or manifold headers – location and size of all pipes and connecting pipes 
3.10.5.Bleeders, mufflers – location, number, size and construction 
3.10.6.Safety valves – size, type and location 
3.10.7.Additional piping or equipment such as condensate removal systems, etc. 
3.11. Pressure Indicating Device/Sensor – Note type, range and location of pressure sensors and 
gauges. 
3.12. Drains including water level dumps, overflows, condensate removal 
3.12.1.Valve type and size 
3.12.2.Pipe size and length 
3.12.3.Note if check valves are used 
3.12.4.Note location of the condensate removal system in relation to critical zones, e.g., relation 
of condensate drain to the bottom of the cook shell in a continuous rotary/reel and spiral 
cooker. 
3.13. Steam supply to the retorts 
3.13.1.Boiler capacity (horsepower, BTU rating), pressure, and method of firing (gas, oil, coal, 
dual capacity). 
3.13.2.Header pressure.  This is important to determine that adequate steam pressure and 
volume is available for the retorting system.  This part of the survey should be performed 
during both peak use and off‐load hours. 
3.13.3.Pipe size and length, valve size and types, pressure regulators or reducers, pipe fittings 
including steam by‐pass pipes, from the main steam line to the test retort(s) 
3.13.4.Size of all connecting steam pipes to the main line, noting all equipment using steam 
(e.g., blanchers, exhaust boxes, etc.). 
3.14. Steam Introduction into the Retort – 

Issue Date: March 13, 2014 
Supersedes Date:  New     3‐2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

3.14.1.Type and specifications for the steam distribution system including configuration (e.g., 
fishtail, cross, in‐line, etc.), steam flow piping, size, number and location of steam injection 
perforations 
3.14.2.Steam injection chamber (if applicable) 
3.14.3.Steam injection points – size, type and location 
3.14.4.Steam spreader or nozzle – shape, size, location and configuration, number, size and 
location of holes in pipe, size of “T”, or any other pipe fittings. 
3.14.5.Describe the heating medium (e.g., steam, hot water) and temperature. 
3.14.6.Describe the cooling medium (e.g., re‐circulated refrigerated water, ambient well water, 
evaporative cooling towers or ponds in re‐circulating cooling water circuits). 
3.15. Air or nitrogen supply to and into the retorts 
3.15.1.Compressor type, capacity and operating pressure 
3.15.2.Type and size of filter, dryer and tank 
3.15.3.Line size, pressure, filters and dryers for instrument air 
3.15.4.Process air header line size(s), pressure and pressure regulation, if used 
3.15.5.Entry location and inlet size, control valve size and type, pressure setting and flow rate 
during testing.  Availability to supply instruments.  Indicate if air is heated or air lines are in 
close proximity to steam or water lines. 
3.15.6.For Overpressure Retorts ‐ Location and size of pipes and valves (type and size) and 
method of control. 
3.16. Water supply to and into the retorts 
3.16.1.Process water supply source, quality, temperature, and controls, if applicable 
3.16.2.Cooling water supply source, quality (including microbial control methods), temperature, 
and controls, if applicable 
3.16.3.Use of any alternate methods of heating processing water 
3.16.4.Describe the method used to heat and cool the processing water including type (e.g., 
heat exchanger, cooling tower, etc.) 
3.16.5.Location and size of pipes, valve size and type, pump and/or spreader size, type and 
location (if applicable) 
3.16.6.Water level indicators – where applicable, type (e.g., sight glass, petcock, electronic, etc.) 
and location 
3.17. Depending upon the retort system, document the following: 
3.17.1.Where applicable, water recirculation system including pump type and capacity, location 
and sizes and filters of inlet/outlet ports, recirculation line size, flow meter type and 
capacity, output rates at operating conditions (e.g., gpm or L/min), rpm, pipe diameter for 
pump inlet and outlet and horsepower rating, impeller size 
3.17.2.Air flow, orifice size, pressure setting and flow rate, if applicable 
3.17.3.Pressure and/or flow switches type, location, and trip point setting, if applicable 
3.18. For Steam/Air Retorts 
3.18.1.Type and description of circulation and mixing system for steam/air mixing; bleeder(s) 
size, type and location 

Issue Date: March 13, 2014 
Supersedes Date:  New     3‐3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

3.18.2.Air Plenum and fan shroud (if applicable) 
3.18.3.Distance (length) from retort shell to plenum material if designed as a “shell in shell”. 
3.18.4.Details on fan shroud design and connection to the plenum 
3.19. For Water Spray and Water Cascading Retorts 
 
3.19.1.Water spreader(s) size, type and location 
3.19.2.Water recirculation system – pump type and capacity, impeller size, motor size, location 
and sizes and filters of inlet/outlet ports, recirculation line size, type and capacity of flow 
meter 
3.19.3.Steam injection points – size, type and location 
3.19.4.Heat exchanger – use, size and type 
3.19.5.Water distribution Plate(s) (Water Cascade) 
3.19.6.Location of water inlet pipe to manifold (e.g., top/center of retort shell, top/rear of retort 
shell) 
3.19.7.Dimensions of manifold and material of construction 
3.19.8.Number, size and location (hole pattern) of holes in water distribution plate; percent 
open area of the holes in the water distribution plate should be calculated (Water 
Cascade) 
3.19.9.Water distribution pipes (Water Spray Retorts) 
3.19.10.Entrance location of entrance of water inlet pipe into retort shell 
3.19.11.Location of water distribution pipes in relation to circumference of retort interior 
3.19.12.Length of pipes, do they extend the length of the retort? 
3.19.13.Number, size and location of holes in pipes 
3.19.14.If connected to nozzles, describe the nozzle type.  Are nozzles fixed or capable of 
oscillation?  Describe if nozzles restrict diameter of the openings. 
3.19.15.Describe water flow rate, e.g., liters per minute, gallon per minute, etc. 
3.19.16.Process water retention channel or trough in bottom of retort 
3.19.17.Note if and how process water is retained for cooling or re‐use 
3.19.18.Length, width and depth of water channel or trough 
3.19.19.Amount of water (liters or gallons) at start of process and how it is controlled and 
measured. 
3.19.20.If applicable, location of steam distributors or spreaders in relation to channel or 
trough. 
3.20. Rotational Equipment – rotational speed indicator and drive system 
3.21. Recording Device – Recorder or recorder/controller type and description including: resolution, 
parameters recorded, and calibration status. 
3.22. Retort Loading Considerations/Loading Equipment 
3.22.1.Container information to include material, size and dimensions, orientation for 
processing (vertical, horizontal, jumbled), and loading configuration (e.g., layered, nested, 
compartmented, offset, etc.) 
3.22.2.Maximum number of containers per layer 

Issue Date: March 13, 2014 
Supersedes Date:  New     3‐4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

3.22.3.Maximum number of cassettes, baskets, or racks per retort 
3.22.4.Cassette, basket or rack dimensions, hole size, configuration and spacing in the base 
plate and sides of cassettes, baskets or racks 
3.22.5.Separator sheet dimension, hole size including open area, configuration, and spacing 
3.22.6.Partial load arrangement, if permitted 
3.22.7.Water displacement requirements (ballast) 
3.22.8.Distance between cassettes, baskets or racks, where applicable 
3.22.9.Orientation of the cassettes, baskets or racks in the retort during processing 
3.22.10.Percent open area of the cassettes, baskets or racks, if used 
3.22.11.Describe basket clamping devices, where applicable 
3.22.12.Describe top and bottom plates holding baskets, where applicable 
3.23. Other Equipment – Other control or functional equipment installed that might affect the 
thermal process study being conducted.  Examples of other types of equipment that should be 
noted include: 
3.23.1.Sampling ports 
3.23.2.Water or condensate level dump valves 
3.23.3.Initial charge and make‐up water systems 
3.23.4.Insulation and/or jacketing of retort shell 

DOCUMENTATION 
Results and observations made should be documented and retained for future reference.  The use of 
digital images may prove useful. 

   

Issue Date: March 13, 2014 
Supersedes Date:  New     3‐5 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

4 CONDUCTING TEMPERATURE DISTRIBUTION TESTS 
Temperature distribution studies are conducted in a sterilizer (retort) using distributed temperature 
measuring devices (TMDs) to establish venting procedures, venting schedules, come‐up requirements, 
temperature stability and uniformity, all of which are necessary to establish reproducible and reliable 
heating and cooling performance throughout the retort.  Temperature distribution studies are typically 
performed using estimated production retort operating conditions or parameters. 

SCOPE 
 
4.1. The guidelines in this chapter are applicable to conducting temperature distribution studies in 
batch saturated steam, steam/air, water immersion, water spray, and water cascade retorts 
operating in both still and agitated modes. 
4.2. Crateless retorts are excluded from the guidelines provided in this document. 
4.3. Continuous Rotary/Reel and Spiral and Hydrostatic retorts are excluded from the guidelines in 
this document. 
 
OBJECTIVES 
 
4.4. The objectives of conducting temperature distribution studies include: 
4.4.1.Establishing venting procedures and schedules (where applicable), come‐up requirements, 
identifying the existence (if any) of slowest to come to process temperature location(s), as 
well as temperature stability and uniformity during the Cook. 
4.4.2.Temperature distribution data may also provide insight into the impact of changes made 
to processing equipment, utilities, and other identified critical factors (e.g., package size, 
type, loading configuration, etc.). 
 
INTRODUCTION and BACKGROUND 
 
4.5. Acceptable temperature distribution is a requirement for process establishment. 
4.6. New retorts require temperature distribution studies.  Similarly, retorts that have undergone 
extensive repair re‐design, or relocation can be expected to require temperature distribution 
studies.  
4.7. Consideration should be given to testing all retorts on a regular basis to confirm they continue 
to perform as previously tested and documented.  The replacement or normal wear of 
components associated with maintaining acceptable temperature distribution also warrant 
consideration for performing temperature distribution studies.  These components may 
include, but are not limited to:  water circulating pumps, valves and pipes associated with 
steam/water flow, steam injectors (fishtails), air orifices, overflow/pressure regulating valves, 
spray nozzles, heat exchangers, water distribution plates, and control system changes.   

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

4.8. Temperature distribution can vary with individual installations of identical equipment at the 
same location.  Consideration should be given to performing temperature distribution in each 
individual retort to document variation within individual retorts. 
4.9. If appropriate, information taken in the processing equipment survey and an understanding of 
plant change control processes, validation, and operation procedures may be used to develop a 
reduced testing plan. 
4.10. Demonstration of adequate temperature distribution is usually a prerequisite for conducting 
heat transfer distribution (where applicable). 
 
MATERIALS, TOOLS, EQUIPMENT 
 
4.11. See Chapter 2 – Test Equipment and Standardization of Test Equipment 
 
METHODS 
 
4.12. Test Retort Selection 
4.12.1.Consideration should be given to testing all retorts in a system.   
4.12.2.When appropriate, a reduced testing plan can be developed based on the information 
taken in the processing equipment survey (see – Chapter 3, Documenting Processing 
Equipment and Test Conditions).  The reasons for retort selection should be documented 
in testing records.  The retort(s) selected should represent the one(s) identified as having 
the greatest potential for diminished delivery of the critical process utilities such as steam, 
air, and water.  Factors that may help identify the test retort (s) include:  retort position 
(e.g., at the beginning or end of a line of retorts, furthest from steam header), container 
configuration, divider sheet style, type of heat transfer medium, and processing partial 
loads. 
4.12.3.The results of the processing equipment survey should be verified for completeness and 
accuracy prior to the start of tests. 
4.13. Test Retort Documentation 
4.13.1.Test retort documentation may include photographs, diagrams, and a description of the 
operation, condition, and calibration status of sensors/measurement devices. 
4.14. Location of Temperature Measuring Devices in the retort 
TMDs should be placed in the following locations: 
4.14.1.Attached or in close proximity to the reference TID probe. 
4.14.2.Attached or in close proximity to the temperature control device, unless the reference 
TID and the controller probe are located together. 
4.14.3.Located in at least two containers filled with test medium for the purpose of determining 
initial product temperatures.  These containers should be located in the positions that are 
representative of the potential worst case locations in the retort load. 
4.14.4.The lowest of initial temperatures to be encountered during normal commercial 
operation should be taken into account in establishing temperature distribution.  The 
Issue Date: March 13, 2014 
Supersedes Date:  New     4‐2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

initial temperature measured should be considered in the context of retort shell and 
basket/crate/rack temperatures which may be lower or higher than the product 
temperatures and could have an effect on the total heat load. 
4.14.5.An adequate number of TMDs are needed to ensure that the slowest to come‐up to 
temperature locations are identified.   A minimum of five (5) TMDs per basket/crate are 
typically used.  These should be located in different layers or otherwise separated in each 
basket/crate in the initial phase of the temperature distribution study.  The intent is to 
determine the slowest to come‐up to temperature location in each basket/crate.  Note 
that additional studies with a higher concentration of TMDs in a particular area or zone 
may be required to verify that the slowest come‐up to temperature location(s) within the 
retort load have been identified. 
4.14.6.TMDs should be placed so those measuring junctions are not in direct contact with 
containers or other surfaces.  All TMDs must be securely fastened in place to prevent 
damage and unplanned movement during the process (particularly in agitating systems). 
4.14.7.In subsequent studies, where no changes have been made to the equipment and 
previous studies have indicated consistency of cold spot location(s), a reduced number of 
TMDs per basket/crate/rack may be sufficient. 
4.15. Location of pressure sensor(s) 
4.15.1.At least one pressure sensor should be located in the retort shell.  If the operational 
pressure sensor has been recently calibrated, it can be used in place of a test device.  
Pressure gauges should also be used to monitor line pressures of steam, air, and cooling 
water during a test. 
4.16. Location of flow meter(s) 
4.16.1.A calibrated flow meter (or alternate method) should be located in a manner to provide 
an accurate record of the water circulation flow during the process cycle in systems using 
circulation pumps. 
4.16.2.A calibrated flow meter (or alternate method) should be located in a manner to provide 
an accurate record of the air flow during the process cycle in systems using air for agitation 
and mixing of process water. 
4.16.3.For steam/air retorts – a calibrated flow meter (or alternative method) may be located in 
the return air plenum to provide an accurate record of the steam/air mixture during the 
process cycle.  If the circulating fan is equipped with a directional/rotational and rpm 
sensing ability of the fan shaft, then the details of the fan motor from the retort survey will 
suffice. 
4.17. Record of Monitored Locations (TMD Map) 
4.17.1.A schematic drawing to show the placement of all monitoring devices within the retort 
should become part of the documentation for the temperature distribution tests. 
4.18. Preparing Retort with Containers 
4.18.1.Container Size – The container size and load density that are likely to be the most difficult 
to achieve temperature uniformity are typically selected for temperature distribution 
studies.  In many cases this will be the smallest container and/or the densest load in use.  

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

In some cases, multiple container sizes, types, configurations and orientations will need to 
be tested. 
4.18.1.1.Since temperature distribution may vary widely with some systems depending 
upon container and type, it may be necessary to study each different container/ type 
and loading condition to develop a different come‐up profile for each size/type and 
loading condition. 
4.18.2.Container Contents – Containers may be filled with water, or the fastest heating product, 
for studying retorts that process convection heating products.  For conduction heating 
products, the containers should be filled with product, starch suspensions, or other 
material that simulates the product.  Regardless of material chosen, caution should be 
exercised when heating characteristics may change with multiple heating cycles.  For 
water immersion, water spray, or water cascade retorts that use a temperature 
“overshoot” in the come‐up profile to help temperature uniformity, use of conduction 
heating containers is often the worst case situation, and should be carefully considered.  
Note that stabilization periods at the end of come‐up are not considered to be overshoots. 
4.18.2.1.For saturated steam retorts, water may be used for conduction heating products; 
however the come‐up times may be somewhat longer than what will occur with 
product. 
4.18.2.2.Document the reasons for ballast container content selection in test 
documentation. 
4.18.3.Container Placement Considerations – Containers are placed in the basket/crate in a 
manner that is equivalent to the worst‐case situation as seen in the commercial operation.  
The worst‐case may be the maximum number of containers per layer, actual number of 
layers, maximum load density, loading pattern, maximum fill of pocket space, and other 
conditions that result in the densest load.  Where vertical channelling is possible, this 
condition should be considered in the temperature distribution test design.  These aspects 
may need to be evaluated through additional testing to ensure that the worst‐case has 
been defined.   
4.18.4.Container Organization – This includes aspects related to baskets, divider sheets, trays, 
racks, and other means of holding or configuring packages in the retort. 
4.18.4.1.The separator or divider sheets should be the same as those to be used in 
production.  If more than one type of separator or divider sheet is used in 
production, then the dividers with the smallest percent open area should be used. If 
additional dividers are used on either the top or the bottom of the container load, 
this procedure must be duplicated for the test. 
4.18.4.2.For a tray or rack that is used to hold and/or separate containers, the design of the 
tray or rack that will be used in production must be used for temperature 
distribution studies. 
4.18.4.3.Variations in basket/crate/rack loading configuration and design expected in 
production may need to be tested to determine which yields the worst‐case 
situation.  The smallest anticipated partial load and location of the partial load 

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

should be compared to full load conditions noting the uniformity and temperature 
control and stability throughout the retort. 
4.19. Conducting the Test 
Data Collection/Monitoring Points – Depending upon the retort system, the following should 
be monitored and recorded during temperature distribution studies. 
All Retorts 
4.19.1.Temperature and Pressure Controller set point(s), including if there is an overshoot set 
point for come‐up and a lower set point for processing 
4.19.2.Product or Ballast Initial Temperature 
4.19.3.Time process cycle starts, Time = 0 (time zero) 
4.19.4.Times when the end of come‐up, start of thermal processing/cook step has been 
achieved, as indicated by either the step change in a control program or the achievement 
of process set‐point temperature at both the reference TID and the recorder/controller 
4.19.5.Reference TID readings at sufficient intervals during the entire cycle, including the point 
in time it reaches the process temperature set point. 
4.19.6.Monitor rotation or agitation rate at sufficient intervals using an accurate calibrated 
stopwatch or calibrated device including any points where rotation rate changes during 
processing or on a continuous chart where rotation or agitation is used. 
4.19.7.Time at the end of thermal process, and start of cool. 
4.19.8.Actual basket/crate/rack orientation in the retort. 
4.19.9.Operating activity of other retorts including the number of retorts entering come‐up 
during the study. 
4.19.10.Numbers and descriptions of other equipment using steam (e.g., blanchers) at the time 
of the study and before, during, and after come‐up. 
 
In addition to the above, these items should be monitored and recorded based on the retort 
being studied: 
 
Steam/Air 
4.19.11.Temperature of air supply entering the retort. 
4.19.12.Water level in relation to spreaders and lowest level of containers in the retort, if 
applicable. 
4.19.13.Time when the pressure set‐point(s) is achieved. 
4.19.14.Time and temperature when the drain is closed, if it is open during a portion of the vent 
if applicable. 
4.19.15.Time and temperature taken from the reference TID when the vent closes. 
4.19.16.Air flow in scfm or liters per minute, if applicable and available. 
4.19.17.Line steam pressure at the time of the test and before, during, and after come‐up, if 
possible. 
4.19.18.Retort pressure, throughout the test cycle at sufficient intervals or on continuous chart. 
 

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐5 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Saturated Steam 
4.19.19.Water level in relation to spreaders and lowest level of containers in the retort. 
4.19.20.Time and temperature when the drain is closed, if it is open during a portion of the 
vent. 
4.19.21.Time and temperature taken from the reference TID when the vent closes. 
4.19.22.Line steam pressure at the time of the test and before, during, and after come‐up, if 
possible. 
4.19.23.Time steam bypass valve closes. 
 
Water Spray and Water Cascade 
4.19.24.Temperature of initial process water. 
4.19.25.Water level in relation to spreaders and lowest level of containers in the retort.  
4.19.26.Flow or recirculation rate of water as determined by flow meter or other acceptable 
means. 
4.19.27.Time when the pressure set‐point(s) is achieved. 
4.19.28.Retort pressure, throughout the test cycle at sufficient intervals or on continuous chart. 
 
Water Immersion 
4.19.29.Temperature of initial process water. 
4.19.30.Fill time (displacement) in those systems dropping water from a storage drum or tank 
into the working processing vessel. 
4.19.31.Water level in process vessel in relation to the top surface of containers, stated as a 
minimum or an actual level throughout the process. 
4.19.32.Flow or recirculation rate of water as determined by flow meter or other acceptable 
means. 
4.19.33.Time when the pressure set‐point(s) is achieved. 
4.19.34.Air flow in scfm or liters per minute, if applicable and available. 
4.19.35.Line air pressure at the time of the test and before, during, and after come‐up, if 
possible. 
4.19.36.Retort pressure, throughout the test cycle at sufficient intervals or on continuous chart. 
4.20. Data‐logger 
4.20.1.The data‐logger should record the temperature of each TMD at sufficient sampling 
frequencies, typically 10‐30seconds, throughout the length of the study.   
4.20.2.The data‐logger should record the temperature from cycle start through completion of 
cooling. 
4.21. Other critical data collection point frequencies 
4.21.1.Assumed or potential process‐related critical factors should be recorded at intervals of 
sufficient frequency to describe and verify retort operating parameters during the test.  
Recordings are part of the permanent test records and should include the temperature 
recording chart, the pressure readings/chart, flow rate records, reference TID readings, 
and other data gathered that were identified as critical data collection points. 

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐6 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

4.22. Study time duration 
4.22.1.The test should extend for at least as long as needed for the retort control system to 
stabilize, establish a definite temperature profile, and all monitoring and TMDs have 
reached a steady‐state condition. 
4.22.2.If desired, retort cooling phase temperatures may be recorded through the entire cooling 
cycle.  This is particularly important if product cooling lethality will be based on actual 
retort cooling profiles in developing scheduled processes. 
4.23. Retort Test Conditions 
Operating Procedures – Normal commercial operating procedures testing the extremes of 
allowable ranges to examine the effects of loading, overpressure, and agitation should be 
followed. 
4.23.1.Temperature distribution studies should be run at the maximum retort temperature to 
be used for commercial processing.  For example, one should not run temperature 
distribution studies at 250°F (121°C) if the product is processed at 266°F (130°C).  
Generally, temperature distribution studies should not be run any higher or lower than 5F° 
(~2.5C°) from the temperature at which product will be processed.   
4.23.2.Minimum vent temperature and time is a critical factor for steam retorts.  The 
temperature and time at which the vent is closed become the minimum vent schedule for 
the process. 
4.23.3.Partial loading conditions should be studied in addition to the full load where permitted. 
4.23.4.Basket rotation should be studied at or below the expected Scheduled Process value. 
 
Where applicable, the following additional conditions may be tested at the standard retort 
processing temperature used for commercial production: 
 
Steam/Air 
4.23.5.High steam to air ratio (Low Overpressure). 
4.23.6.Low steam to air ratio (High Overpressure). 
 
Water Spray, Water Cascade, and Water Immersion Retorts 
4.23.7.Low flow of the heat transfer medium. 
 
4.24. Replication – To demonstrate reproducibility, at a minimum duplicate temperature 
distribution studies should be performed for each situation (e.g., container size, container type, 
operating temperature, basket/crate/rack system) with uniform and comparable results 
obtained from each test. 
4.25. Post‐test inspection 
4.25.1.The condition of the measuring sensors, the test containers, and other attributes of the 
retort load should be examined after the completion of the entire set of studies to 
determine if the test results may have been affected by movement or other changes to the 
desired test setup. 

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐7 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

 
DATA ANALYSES 
 
4.26. Plot or tabulate the minimum and maximum measured temperatures for all TMDs within the 
retort load at each scan/time interval.  The TID, Controller, and Chart temperatures at specific 
time points should be evaluated relative to the TMD’s temperature. 
4.27. Evaluate the difference between the minimum measured temperature and the programmed or 
set‐point minimum process temperature at specific time points to establish or confirm 
temperature off‐sets and to establish come‐up time. 
4.28. Identify the location of the TMD that was the slowest to achieve come‐up criteria.  Identify the 
time this TMD achieved come‐up criteria. 
4.29. Identify the minimum Initial Temperature. 
 
SUCCESS CRITERIA 
 
4.30. Come‐Up –  
4.30.1.The TID should be at or above minimum process temperature at the end of come‐up.   
4.30.2.All TMDs should be within 1F° (0.5C°) of minimum process temperature at the end of 
come‐up.   
4.30.3.All TMDs should be at or above the minimum process temperature within 1 minute of 
starting the hold time.    
4.31. Cook/Hold –  
4.31.1.After the start of Hold, the TID should not fall below the minimum process temperature. 
4.31.2.After the first minute of the Hold phase, the uniformity and stability of temperatures is 
confirmed by having no TMD temperature fall below minimum process temperature once 
that TMD has reached the minimum process temperature. 
4.32. Cooling – If specific cooling profiles are critical to the process delivery, the temperature 
distribution during cooling must support those profiles. 
4.33. Other –  
4.33.1.The location of all TMDs must be confirmed at the end of all studies.  Any TMD that 
shifted during data collection should be evaluated for impact on study outcomes. 
4.33.2.The integrity of test packages/ballast should be confirmed to be acceptable. 
4.33.3.All critical retort operating parameters (e.g., Temperature, Rotation, Pressure, Flow, 
Water Level, and Fan Speed) were achieved as planned and/or programmed. 
4.33.4.Situations or conditions that do not meet these criteria should be critically evaluated. 
4.33.5.Identify the minimum Initial Temperature for which the temperature distribution is valid. 
4.33.6.Identify all other aspects of the product, package, ballast, loading pattern, and so forth 
for which the temperature distribution is valid. 
 
 
 
Issue Date: March 13, 2014 
Supersedes Date:  New     4‐8 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

DOCUMENTATION 

Temperature distribution findings should be summarized in a report.  Supporting items that should be 
included are: 

4.34. Reason(s) for retort selection. 
4.35. Results from the retort survey and test retort documentation. 
4.36. Schematic showing placement of all measuring devices in the retort. 
4.37. Reason(s) for product selection. 
4.38. Retort charts, operator logs, retort control program, and control system reports. 
4.39. Critical point observations to include Initial Temperature. 
4.40. Calibration information for all sensors/devices used. 
4.41. Data‐logger data for both retort and product. 
4.42. Graphical depictions of minimum/maximum data. 

   

Issue Date: March 13, 2014 
Supersedes Date:  New     4‐9 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

5 CONDUCTING HEAT TRANSFER DISTRIBUTION TESTS 
This Guideline covers the scientific basis and fundamentals for conducting Heat Transfer Distribution 
Studies with emphasis on critical elements to be considered.  This Guideline provides rationale for 
considerations to be used by an end user in deciding when Heat Transfer Distribution Studies are 
needed in addition to Temperature Distribution Studies. 

SCOPE 
 
5.1. The guidelines in this chapter are applicable to conducting Heat Transfer Distribution Studies in 
steam/air retorts and may be applied to water spray, water cascade, and water immersion 
retorts where air overpressure in excess of the saturated steam pressure (corrected for 
altitude) at process temperature is used. These guidelines are applicable to retorting systems 
operating in both still and agitated modes. 
 
 
OBJECTIVES 
 
The objectives of Heat Transfer Distribution Studies include: 
5.2. Identification of the slowest to heat location in a retort to the extent that it impacts process 
delivery within the retort load when using the same process, product, package, and load 
conditions.  Load Conditions include: Partial loading of baskets (e.g., less than a full basket of 
trays), less than a full retort load (e.g., 4 baskets in a 5‐basket retort), tray/racks loading (e.g., 
not all package locations filled with a package), and density and/or percentage of open 
volume/void volume. 
5.3. Identification of the repeatability of those relatively slower to heat locations across retorts and 
studies using the same process, product, package, and load conditions. 
5.4. Identification of recommended locations to place Heat Penetration containers for Process 
Establishment. 
5.5. Verification of the adequate delivery of the thermal process over time for a given 
product/package combination and loading condition(s). 
 
INTRODUCTION and BACKGROUND 
 
5.6. Temperature Distribution testing usually focuses on come‐up and cook portions of the retort 
cycle.  Temperature uniformity in these portions of the retort cycle may not always correlate to 
adequate heat transfer into packages throughout the retort, hence the need for Heat Transfer 
Distribution studies. Acceptable Temperature Distribution is recommended prior to conducting 
Heat Transfer Distribution Studies. 
5.7. Heat Transfer Distribution testing may be recommended when: 

Issue Date: March 13, 2014 
Supersedes Date:  New     5‐1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

5.7.1.A non‐condensable gas such as nitrogen or air is introduced into the heat transfer medium 
to provide overpressure in excess of the saturated steam pressure (corrected for altitude) 
at the Cook Temperature. 
5.7.2.For heating medium delivery systems (including type, flow, rack, package, etc.) whenever 
it is possible that in certain areas of the retort load the rate of heat energy supplied to the 
package is not in excess of the rate at which the package can absorb the heat energy. 
5.7.3.For new retorts, new retort programs/controls, new product/package/closure 
combinations including trays/racks/load configurations requiring overpressure air in 
excess of the saturated steam pressure at Cook Temperature. 
5.7.4.As part of an overall Change Control Program. 
5.7.5.When partial loads may be processed during manufacturing. 
5.7.6.Any time there are concerns that heat transfer delivery may be impacted by the retort’s 
heating medium mixing and distribution system such as the presence of a fan, nozzles, 
shrouds/plenum, racking/tray design, and so forth. 
5.8. Heat Transfer Distribution data may assist in conducting deviation analyses provided data are 
collected using actual product and package. 
5.9. Heat Transfer Distribution data can be used as part of an overall ongoing program to verify 
retort operations over time. 
5.10. The effects of package location along the radius of rotating loads are often not considered in 
Temperature Distribution testing, nor are effects of fastest to heat packages compared to those 
that are fastest to cool.  Heat Transfer Distribution Studies may provide insight into potential 
effect of location along the radius of rotating loads as well as effects of faster to heat and cool 
packages within the retort load.   In addition, insight may be gained on retort fan position, 
heating medium/air inlet design and shroud design, and their influence on the flow and mixing 
of the heating medium. 
5.11. If desired, lethality data collected using actual packaged product (vs. non‐product based HIUs) 
may be separated into that achieved during come‐up and cook versus that achieved in cool.  
This information may be valuable in assessing the effects on nutrients and the product’s 
physical stability throughout the retort load.  Modifications to the retort, package, loading 
configurations, trays/racks, processing cycle, etc. to reduce or minimize the lethality differential 
throughout the load may be then possible.  Note that Heat Transfer Distribution data are not 
used for Process Establishment. 
5.12. As part of an overall Change Control program, Heat Transfer Distribution data collection should 
be considered whenever: 
5.12.1. Changes are made to packaged product loading such as new or modified trays, baskets, 
etc. are introduced. 
5.12.2.Changes are made to load density, flow rate of heat transfer medium, and shroud design. 
5.12.3.Changes are made to the primary package (e.g., heavier bottle), change to package fill 
volume and/or headspace volume, etc. 
5.12.4.New formulations are introduced. 

Issue Date: March 13, 2014 
Supersedes Date:  New     5‐2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

5.12.5.Changes are made to utilities or the retort such as those done as part of upgrades to 
equipment or significant repairs. 
5.12.6.The amount of air overpressure in excess of saturated steam pressure (when corrected 
for altitude) at Cook Temperature is modified. 
5.12.7.Partial loads are to be processed. 
5.13. Heat Transfer Distribution studies, in contrast to Heat Penetration studies, must always be 
conducted in the production retort(s).  Pilot Plant Retorts or Research Simulators should not be 
used for studying or extrapolating Heat Transfer Distribution performance.
5.14. Microbiological techniques are not recommended for Heat Transfer Distribution studies. 
5.15. Temperature and pressure must be independently controlled and recorded. 
 
MATERIALS, TOOLS, EQUIPMENT 
 
5.16. See IFTPS Guidelines for Conducting Thermal Processing Studies, Chapter 2 – Test Equipment 
and Calibration of Test Equipment. 
5.17. Heat Transfer Distribution measurements may be obtained from instrumented/probed:‐  
5.17.1.Product‐filled packages; or 
5.17.2.Non‐product based HIUs made from polymer‐based materials such as Teflon, clays such 
as bentonite suspensions, and oils.  Please refer to, Section 2.14.11 for criteria regarding 
use of non‐product based HIUs. 
5.18. A sufficient number of instrumented/probed samples to ensure that all areas of the retort load 
are being studied and to support statistically valid analyses must be included in each study. 
 
METHODS 
Test Retort Selection 
5.19. In general, all of the information taken in the processing equipment survey should be used to 
select the retort(s) that will be used for Heat Transfer Distribution Studies.  The reasons for 
retort selection should be documented in testing records or all retorts should be studied.   
5.20. The retort(s) selected should represent the one(s) identified as having the greatest potential 
for diminished mixing and delivery of the heat transfer medium. 
5.21. Heat Transfer Distribution Studies must be conducted using production retorts under expected 
production and operating conditions. 
Test Retort Documentation 
5.22. Information based on data from the processing equipment survey and from Temperature 
Distribution Studies should be included in study documentation. 
5.23. The specific process, product, package, and load conditions being studied must be 
documented. 
Ballast Retort Load 
5.24. The ballast used may be product‐filled packages of the type and size being evaluated.  
Alternatively, other materials may be used provided their heating characteristics are consistent 
with the product being studied. 
Issue Date: March 13, 2014 
Supersedes Date:  New     5‐3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

5.25. Ballast packages should retain their heating and physical characteristics if they are to be re‐
used.  Re‐use of ballast packages should be documented in a Test Report.   
5.26. Note that water‐filled packages generally should not be used as ballast for Heat Transfer 
Distribution Studies to allow the retort controls to perform representatively for heating media, 
delivery and its replenishment within the load. 
Baskets/Trays and Loading Considerations 
5.27. The loading conditions used or expected to be permitted during manufacture of packaged 
product must be studied.  This includes using the baskets, trays/racks, dividers, cassettes, etc. 
that will hold/carry product‐filled packages. 
5.28. Load density may have a dramatic impact on Heat Transfer Distribution.  This is due to 
inhibition or retardation of distributing the heat transfer medium throughout the retort load.  
Therefore, optimization with respect to the specific retort’s heat transfer medium mixing and 
distribution should be considered wherever possible.  Optimization factors to consider include 
the design of: 
5.28.1.Trays/racks/baskets, 
5.28.2.Package, 
5.28.3.Number of packages per layer/rack/basket, and 
5.28.4.Retort operating parameters such as temperature and pressure values and ramps, timing 
of air introduction, any venting at the start of the retort cycle, or pre‐heating of the 
overpressure air. 
Locations of Probed Packaged Product/HIU in the retort 
5.29. Heat Transfer Distribution test units are placed in suspected or known slower to heat locations 
within the retort load.  Multiple studies may be required to confidently identify the slower to 
heat locations within the retort load.   
5.29.1.TMDs to measure temperatures surrounding the test packages should be located in 
proximity to those test packages.  These TMDs are to be used to accurately calculate fh 
values of adjacent test packages. 
5.30. TMDs to measure product/HIU temperatures to be used for data analyses should be securely 
fastened inside the test package so that the measuring junction/tip is held in the test package 
cold spot. 
5.31. At a minimum, five (5) probed product packages/HIUs should be located in separate suspected 
or known slower to heat areas of each basket.  Symmetry and rotation effects should also be 
considered when determining locations for Heat Transfer Distribution test units. 
5.32. All baskets in the retort should contain test units. 
Location of pressure sensor(s) 
5.33. Independent verification of total retort pressure during Heat Transfer Distribution Studies is 
recommended when possible and practical. 
Location of flow meter(s) 
5.34. Independent verification of flow rates of the heating medium is recommended when possible 
and practical. 
Record of Monitored Locations (Loading Pattern/Map) 

Issue Date: March 13, 2014 
Supersedes Date:  New     5‐4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

5.35. A schematic drawing to show the placement of all monitoring devices within the retort should 
become part of the documentation for Heat Transfer Distribution Studies. 
Retort Control and Process Conditions 
5.36. Heat Transfer Distribution Studies should be conducted using the process parameter conditions 
such as temperature, pressure, mixing and distributing the heat transfer medium, and rotation 
set‐points used during normal production or manufacture of the packaged food being studied. 
5.36.1.Since fh and the associated %CV are used as the primary measures to assess adequacy of 
Heat Transfer Distribution, data do not necessarily need to be collected at the highest 
allowed overpressure permitted for the product/package being evaluated.  This is in 
contrast to Heat Penetration studies where all “worst case” retort conditions and 
parameters must be used.It is important that the amount of overpressure used during 
Heat Transfer Distribution Studies be representative of the expected production condition 
for the product/package being studied. 
Conducting the Test 
5.37. Data Collection/Monitoring Points – Heat Transfer Distribution test units must be located in 
suspected or known slower to heat locations within the retort load.  Independent verification of 
parameters such as controlling temperature, pressure, heat transfer medium flow rates, etc. is 
recommended.  Location of independent sensors is at the discretion of the persons responsible 
for the study design. 
5.38. Scan Frequency for Measurement Devices 
5.38.1.Where possible, measurement devices should be set to a scan frequency sufficient to 
accurately determine heating parameters (i.e., fh). 
5.39. Study time duration 
5.39.1.Cook durations should be of sufficient length to adequately determine fh values and to 
confirm that Temperature Distribution success criteria were satisfied (See Temperature 
Distribution success criteria). 
5.40. Replication 
5.40.1.At a minimum, duplicate Heat Transfer Distribution Studies should be performed for each 
situation (e.g., package size, package type, operating temperature, basket/tray/rack 
system, etc.) with uniform and comparable results obtained from each test.  Success 
Criteria must be met in all replicate studies. 
5.40.2.Replicates should be true replicates in all respects, including Initial Temperature, Retort 
Temperature, Pressure, rpm, and so forth. 
5.41. Pre‐ and Post‐test inspections 
5.41.1.See Chapter 2 –Test Equipment and Calibration of Test Equipment. 
5.41.2.The fabrication, accuracy, condition of the HIUs, the product‐filled test packages, and 
other attributes of the retort load should be examined before Heat Transfer Distribution 
are initiated to determine if they are acceptable for use and Heat Transfer Distribution 
results using them will not be adversely affected by the testing sub‐systems. 
5.41.3.The condition of the measuring sensors, the HIU/product‐filled test packages, and other 
attributes of the retort load should be examined after the completion of the test to 

Issue Date: March 13, 2014 
Supersedes Date:  New     5‐5 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

determine if the test results may have been affected by movement of these sensors or 
other changes to the desired test setup. 
5.41.4.Comparison of pre‐ and post‐test fill weights to ensure test packages have not leaked 
during testing.  Consideration should be given to discarding data from leaking packages. 
 
DATA ANALYSES 
 
5.42. Calculate fh values and the associated % CV 
5.43. Identify the slower to heat locations within the retort load, e.g., fh distribution within the 
retort. 
5.44. Confirm adequate Temperature Distribution including come‐up time. 
5.45. Confirm that retort control and process conditions were achieved as designed. 
5.46. If HIUs/product‐filled test packages have also been placed in faster to heat locations, the fh 
differential between slow and fast to heat locations may also be compared. 
5.47. Determine product slower and faster to heat locations for the HIUs/product‐filled test package 
combination.  The slowest to heat location is determined based on the largest fh value. 
5.48. All subsequent process determination studies, i.e. Heat Penetration, should be conducted 
placing test packages in the known slowest to heat locations determined from Heat Transfer 
Distribution studies. 
5.49. If desired, determine product slowest and fastest to cool locations. 
 
SUCCESS CRITERIA 
 
Heat Transfer Distribution may be considered acceptable when:  
5.50. Temperature Distribution success criteria have been met during each Heat Transfer 
Distribution Study. 
5.50.1.Note that demonstration of adequate Temperature Distribution is recommended prior to 
conducting Heat Transfer Distribution Studies. 
5.51. Retort control and process conditions achieved/met as designed. 
5.52. fh % CV ≤ 5% within and across replicate studies.  When this condition is met, uniform heat 
transfer conditions have been confirmed and Heat Penetration probes may be located 
anywhere in the retort. 
5.52.1.In the event the fh CV is found to be>5%, it should first be confirmed that the sensors 
used were consistent with accuracy stipulations (see Chapter 2 – HIU).  Additional Heat 
Transfer Distribution studies need to be conducted to ascertain that the slowest to heat 
locations have been reliably and consistently determined, with appropriate confidence and 
rigor.  Thereafter, all Process Establishment Heat Penetration Studies for the test (i.e. 
product, package, process, retort and load) combination need to be conducted at the 
identified slowest to heat locations. 
5.52.2.Alternatively, when the %CV is >5%, iterative changes could be made to the retort, retort 
control, load density, rack design, etc. in an attempt to achieve an fh % CV ≤ 5%.  Once 

Issue Date: March 13, 2014 
Supersedes Date:  New     5‐6 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

changes have been completed, replicate Heat Transfer Distribution studies should be 
conducted.  Note that temperature distribution studies are a pre‐requisite to conducting 
heat transfer distribution studies.  The need to collect temperature distribution data after 
making changes should be evaluated prior to conducting additional heat transfer 
distribution studies. 
5.53. Verified that the retort is uniform in terms of heat transfer media distribution and delivery 
and/or the slowest to heat location(s) within the retort load that may be used for Heat 
Penetration studies for Process Establishment have been identified. 
5.54. If product‐filled packages are used, product functionality and seal integrity are within accepted 
parameters. 
 
RISKS, ISSUES, AND OTHER CONSIDERATIONS 
 
5.55. HIU geometry should not interfere with the normal flow pattern and mixing of the heat 
transfer medium within the retort load. 
5.56. Heat Transfer Distribution data are not used for Process Establishment. 
5.57. fh values determined from HIU other than actual the product/package may not be used for 
deviation evaluations. 
5.58. Sufficient quantity of probed packages/HIU to conduct a valid statistical evaluation of the fh 
variability within a test is required.  Typically this will require that more than 6 values are used 
to calculate a mean fh and the associated standard deviation and %CV.  In general, a larger 
number of values will provide more robust values. 
5.59. Replicate studies are recommended.  The number of replicate studies will depend upon the 
number of retorts being evaluated and whether you are studying a new 
retort/process/package/formulation or if this is part of a periodic (e.g., annual) re‐verification 
program.  When replicate studies fail to meet Success Criteria for Heat Transfer Distribution, 
additional studies are needed. 
5.60. Since fh and the associated % CV are used as the primary measures to assess adequacy of Heat 
Transfer Distribution, data do not necessarily need to be collected at the highest allowed 
overpressure for the product/package being studied.  This is in contrast to Heat Penetration 
studies where the “worst case” retort conditions as defined by the Scheduled Process must be 
used.   It is important that the amount of overpressure used during Heat Transfer Distribution 
Studies be representative of the expected production condition for the product/package being 
studied. 
5.61. Non‐product based HIUs may be a preferred option to product‐filled packages when the food 
being studied heats primarily by conduction. 
 
DOCUMENTATION 
 
Documentation of heat transfer distribution studies should include: 
5.62. Reason(s) for retort selection. 
Issue Date: March 13, 2014 
Supersedes Date:  New     5‐7 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

5.63. Results from the retort survey and test retort documentation including digital photos showing 
the heating media delivery system including fans, pumps, nozzles, spreaders, shrouds, and so 
forth. 
5.64. Schematics and/or digital photos showing placement of all monitoring devices in the retort. 
5.65. Reason(s) for use of the specific HIU selected, i.e., packaged product vs. non‐product based 
HIU. 
5.66. Reason(s) for use of the specific Ballast selected, i.e., packaged product, packaged water or 
HIU. 
5.67. Schematics and digital photos or packages, HIUs, Racks, Trays and Loads used for testing. 
5.68. Retort charts, operator logs, retort control program, and control system reports 
5.69. Critical factor records. 
5.70. Calibration information for all sensors/devices used. 
5.71. Raw data for both Temperature and Heat Transfer Distribution probes and that for any other 
monitoring devices such as pressure sensors that were used during the study. 
5.72. Data and statistical analyses, re‐tests, results and discussion as part of a Heat Transfer 
Distribution Testing Report, documenting testing deviations, findings, success criteria and 
recommendations for additional/subsequent work. 

   

Issue Date: March 13, 2014 
Supersedes Date:  New     5‐8 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

6 CONDUCTING HEAT PENETRATION STUDIES 
SCOPE 
 
The guidelines in this chapter apply to conducting heat penetration studies in any retort system 
including saturated steam, steam/air, water spray, water cascade, water immersion, and crateless.  
Batch retorts may be operated in either the still or agitating mode.  Considerations for collecting 
heat penetration data in continuous rotary/reel and spiral and hydrostatic retorts are included.  The 
intent of this document is to provide guidance in regards to the preparation and execution of heat 
penetration studies.  Suggestions regarding data analysis of heat penetration data are also provided. 

OBJECTIVES 
 
6.1. The purpose of a heat penetration study is to determine the heating and cooling behavior of a 
product/package combination in a specific retort system for the establishment of safe thermal 
processes to deliver commercially sterile products and to assist in evaluating process 
deviations.  
6.2. The study must be designed to adequately and accurately examine all critical factors associated 
with the product, package and process which affect heating rates.  
6.3. Before commencing a heat penetration study, where applicable, an evaluation of retort 
temperature distribution and heat transfer distribution should have been completed.  
6.4. A goal in conducting these studies is to identify the worst case temperature response expected 
to occur in commercial production as influenced by the product, package and process. 
 
INTRODUCTION and BACKGROUND 
 
Several product, process, package and measurement related factors can contribute to 
variations in the time‐temperature data gathered during a heat penetration test. Establishment 
of a process requires expert judgment and sound experimental data for determining which 
factors are critical and the effect of changing those factors both within and beyond established 
critical limits. The list of items addressed in this section is extensive, but should not be assumed 
to cover all possible factors. Quantitative data on variability should be recorded where 
appropriate and all pertinent data should be documented to better understand and account for 
possible variations in heat penetration behavior. 
 
6.5. Product 
6.5.1. Product formulation and weight variation of ingredients should be consistent with worst 
case production values.  Changes in formulation may necessitate a new heat penetration 
study. 
6.5.2. Fill weight used for heat penetration studies should not be less than the maximum 
declared on the process schedule. Excess product may be expressed as percent overfill. 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

6.5.3. Solids content should be measured for nonhomogeneous products both before and after 
processing. Solids content deposited in a sieve should be weighed and expressed as a 
percentage of total weight. Note: Addition of compressed or dehydrated ingredients may 
result in increased drained weight. 
6.5.4. Note that solids content may be considered a critical factor for homogeneous products 
and should be measured before processing. 
6.5.5. Consistency or viscosity of semi‐liquid or liquid components should be measured before 
and after processing. Flow behavior will change with type and concentration of thickening 
agents (e.g., starch, gums, etc.), temperature and shear rate. Changes may be reversible 
or irreversible which may be important when reprocessing product. 
6.5.6. Size, shape and weight of solid components should be measured before and after 
processing, when appropriate.  For example, measuring size and shape of cooked rice in 
product may not be possible or useful. 
6.5.7. Integrity and size of solid component clusters may change during processing and affect 
temperature sensor placement in the product and cold spot location. 
6.5.8. Methods of product preparation prior to filling should simulate commercial practice. For 
example, blanching may cause swelling, matting or shrinkage which could influence heat 
penetration characteristics. 
6.5.9. Product matting or clumping may change heat penetration characteristics and influence 
cold spot location. Also, caution should be exercised with sliced products which may stack 
together during processing. 
6.5.10. Rehydration of dried components, either before or during processing, is a critical factor 
which may influence heat penetration behavior, as well as process efficacy with respect 
to spore inactivation. Details of rehydration procedures should be recorded during the 
heat penetration study. 
6.5.11. Product may heat by convection, conduction or mixed convection/conduction 
depending on its physical properties. Heating properties may also be influenced by 
presence/absence of agitation during processing, headspace volume, etc.   
6.5.12. Some foods exhibit complex (broken) heating behavior. Product may initially heat by 
convection, then due to a physical change in the product, change to conduction heating 
behavior. For example, for products such as soups which contain starch, a change in 
heating behavior may be due to starch gelatinization at a particular temperature. Small 
variations in product formulation or ingredients may cause the transition from convection 
to conduction heating to occur at a different temperature and related time. Special care 
should be taken to identify and control specific product and process variables related to 
the heating rates of these products. 
6.5.13. Additional product characteristics such as salt content, water activity, pH, specific 
gravity, concentration of preservatives, and methods of acidification may influence heat 
transfer or microbiological resistance and should be recorded. 
 
 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

6.6. Container 
6.6.1.Manufacturer and brand name information for the container should be recorded in case 
information related to filling, sealing or processing is required. 
6.6.2.Container type (metal cans, glass jars, retort pouches, semi‐rigid containers); size and 
dimensions should be recorded. 
6.6.3.Nesting of low profile packages can influence heating behavior. Heat penetration studies 
where nesting can occur, including jumbled loads, should include tests conducted on 
stacks of packages as well as non‐nested packages.   
6.6.4.Container vacuum and headspace should be recorded for rigid containers. For flexible and 
semi‐rigid containers, the volume of residual gases in the container should be determined. 
Entrapped and dissolved gases may create an insulating layer in the container causing a 
shift in the cold spot location and a decrease in the heating rate. Controlled overpressure 
during processing has been found to reduce these effects. 
6.6.5.Maximum thickness of flexible packages (pouches) has a direct relationship to the cold 
spot temperature history with thicker packages heating more slowly. Heat penetration 
studies should be carried out at the maximum specified and permitted package thickness. 
6.6.6.Container orientation (vertical, horizontal, and specific location of top/bottom of the 
package) within the retort may be a critical factor for some product/package combinations 
and should be studied, where appropriate. Changes in container orientation may also 
influence vent schedules and come‐up time as well. 
6.6.7.Post‐processing examination of test containers for abnormalities should be conducted 
with special emphasis on the slowest and fastest heating containers. It is strongly 
recommended that flexible packages be carefully examined following processing to 
identify the thermocouple junction location. If the intended sensing location has shifted, it 
is likely that heat penetration data collected are not reliable. 
 
6.7. Method of Fill 
6.7.1.Fill temperature of the product should be controlled. It will affect the initial temperature 
which may influence some heat penetration parameters (lag factor, retort come‐up 
period). This may constitute a critical factor for a process, particularly for products which 
exhibit broken heating behavior. 
6.7.2.Fill and net weights may influence heating rates both in still and rotary cooks. Information 
on variability may be found in statistical process control and product quality control 
records. 
6.7.3.In most cases, controlling headspace by determining net weight is not sufficient due to 
possible variations in the specific gravity of the food product. Care should be taken to 
avoid incorporation of air which would affect the headspace vacuum. In rotary processes, 
container headspace is a critical factor since the headspace bubble helps mix the product 
during agitation. 
 
 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

6.8. Closing or Sealing 
6.8.1.Closing or sealing equipment should provide a strong, hermetic seal which is maintained 
during the thermal process. 
6.8.2.Vacuum is affected by variables such as: headspace, product temperature, entrapped air, 
and vacuum efficiency of the closing equipment.  
6.8.3.Some products such as vegetables vacuum‐packed in cans may have a minimum vacuum 
as a critical factor. For others packed in flexible or semi‐rigid containers, vacuum setting 
will influence the residual air content in the package, also constituting a critical factor. 
 
6.9. Retort  System ‐ The type of retort system used may have a significant influence on the heating 
rates of products processed in the retort. Results from a heat penetration test should be 
reported with reference to the retort type, heat transfer medium, agitation, and other pre‐
defined conditions existing at the time of testing. 
6.9.1.When testing convection and conduction heating products, retort come‐up time should be 
as short as possible consistent with obtaining satisfactory temperature distribution.  
Results will be conservative when using laboratory size retorts or simulators as these tend 
to have shorter come‐up times and cool more quickly than production retorts.  However, 
caution should be exercised when processing broken heating products where the length of 
the come‐up period may affect the time at which the product heating characteristics 
change from convection to conduction.  This may also be of concern where come‐up times 
are longer in production than defined by the designed process. 
6.9.2.Laboratory size retorts or simulators may be used for development work on heat 
penetration behavior. After development, the thermal process should, if physically 
possible, be verified in an appropriate production retort. 
6.9.3.Heat transfer distribution studies should be conducted prior to conducting heat 
penetration studies for overpressure retort systems. 
6.9.4.Racking systems may be used to separate layers of cans or jars; constrain the expansion of 
semi‐rigid and flexible containers; provide support and circulation channels for thin profile 
containers; and ensure maximum pouch thickness is not exceeded. Care should be taken 
to understand the influence of a specific rack design on retort performance and heat 
transfer to containers. 
6.9.5.Still batch retort systems vary in operation based on: type of heating medium(e.g., steam, 
steam/air, water); orientation of the retort (vertical, horizontal); method of heating 
medium agitation (fans, pumps, air injection); and other factors which may influence the 
heating behavior. 
6.9.6.Rotational batch retort systems (e.g., axial, end‐over‐end) are designed to rotate (or 
oscillate) entire baskets of product during processing. Container agitation may provide 
faster rates of heat penetration to the container cold spot as compared to still cooks. 
6.9.7.It is recommended that data be collected at small time increments (e.g., 15‐seconds or 
less) particularly for low viscosity fluids where the cold spot may move in relationship to a 
fixed TMD during rotation, producing erroneous results. Short time intervals are important 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

with low viscosity liquids and broken heating products that change from convection to 
conduction.   Slightly longer time intervals (e.g., 30‐seconds) may be acceptable for 
conduction heating products.  1 minute is adequate for most conduction heating products, 
and 3 minutes may be adequate for large containers of conduction heating products 
where the process time is longer.  In general, 50 to 100 data points collected over the 
collection time may be sufficient for many conduction heating products.   
6.9.8.Slip‐ring connectors should be cleaned and TMD calibration verified at regular intervals. 
Critical factors for rotational batch retorts may include: headspace, product consistency, 
solids to liquid ratio, initial temperature, container size, rotational speed and radius of 
rotation. 
6.9.9.Continuous retort systems move containers through the processing vessel along a spiral 
track located at the outside circumference of a horizontal retort shell or may be carried 
through a hydrostatic retort in chain driven flights. Regardless of the configuration, it 
becomes difficult or impossible to use thermocouples to collect heat penetration data in 
these systems. Data may be obtained using simulators and then confirmed using wireless 
data‐loggers in the commercial vessel. 
6.9.10.Heat penetration data, in some cases can be collected using process simulators.  An 
understanding of scaling or other differences between commercial vessels and the process 
simulator and the impact on heat penetration is needed and should be documented.

MATERIALS, TOOLS, EQUIPMENT 
 
6.10. See Chapter 2 – Test Equipment and Calibration of Test Equipment  
 
METHODS 
 
6.11. Positioning of Temperature Measuring Devices (TMDs) in the Container 
6.11.1. The method of inserting a TMD into a container should result in an airtight, watertight 
seal which should be verified after testing.  Verification may be accomplished through 
comparison of container weights recorded pre‐and post‐testing. 
6.11.2.TMD sensing junctions should be positioned in the cold‐spot of the package.   
6.11.3.During insertion of the TMD, caution must be taken to avoid physical changes to the 
product components such as creating a conduction pathway to the particulate center. Care 
should also be taken to address potential agitation created by the probe, which can occur 
in rotation processes if the probe acts as a stirrer. 
6.11.4.The method employed for mounting the TMD into the container should not affect the 
container geometry which could influence heat penetration characteristics. 
6.11.5.Flexible or rigid TMDs may be inserted into rigid, flexible or semi‐rigid containers using 
compression fittings or packing glands. For flexible containers, NFPA (4) provides 
illustrations of thermocouple positioning into a solid particulate and several thermocouple 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐5 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

positioning devices to ensure the thermocouple remains in a fixed position within the 
container.  
6.11.6.The most appropriate TMD device for a particular application will depend upon the 
product, racking system, container type and sealing equipment. 
6.11.7.Leakage may be detected by weighing the container before and after processing to 
determine changes in gross weight. If there is leakage caused by improperly mounted 
TMDs or the failure of a hermetic seal, data collected for that container should be 
discarded. 
6.12. Type and Placement of Containers 
6.12.1.The type and size of container used in the heat penetration study should be the same as 
that used for the commercial product.  
6.12.2.The racking and loading of rigid (e.g., cans), semi‐rigid (e.g., plastic bottles, trays and 
cups) and flexible (e.g., pouches) containers should simulate commercial practice.  
6.12.3.Test containers should be placed at the slowest heating location(s) in the retort, as 
determined by temperature and heat transfer distribution studies. 
6.13. Temperature of the Heating Medium 
6.13.1.TMDs to measure the heating medium should be positioned so as to prevent direct 
contact with racks or containers and identified according to their specific locations in the 
retort.  
6.13.2.A minimum of two TMDs are recommended for retort temperature measurement: one 
situated close to the sensing bulb of the retort reference TID, the other located near the 
test containers.  
6.13.3.In addition, at least one TMD should be placed near the sensor for the temperature 
controller when that location is remote from the location of the reference TID. 
6.14. Retort Pressure ‐ Worse case overpressure conditions should be used when collecting heat 
penetration data. 
6.14.1.Overpressure conditions during processing will influence package expansion by 
constraining the expansion of headspace gases. This may be beneficial by improving heat 
transfer to food in flexible and semi‐rigid containers or detrimental by restricting the size 
of the headspace bubble in rotary processes.  
6.14.2.Cooling without overpressure may result in depressurization within a container at the 
end of a process, leading to accelerated decreases in temperature for fluid foods.  Glass 
packages may also break if overpressure is not properly maintained during cooling. 
6.15. Cold Spot Determination 
6.15.1. The location of the slowest heating or cold spot in a container is critical to establishing a 
process and should be determined experimentally. A cold spot location study should be 
completed to determine the slowest heating location for a specific 
product/package/process combination. Usually, the cold spot location will be determined 
from a series of heat penetration tests employing several containers with TMDs inserted at 
different locations. Alternatively, more than one TMD per container may be used; 
however, multiple TMDs may influence heating behavior, especially for products in smaller 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐6 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

containers (6).  Care and judgement based on a number of preliminary experiments, must 
be exercised to ensure the cold spot location has been identified.  
6.16. Initial Product Temperature 
6.16.1.Measurement of initial product temperature should be taken immediately prior to 
testing. 
6.17. Number of Containers per Test Run 
6.17.1.A heat penetration test should evaluate at least 10 working TMDs for each test run (6). If 
the retort cannot accommodate this quantity, the number of replicate test runs should be 
increased. 
6.18. Number of Test Runs 
6.18.1.Replication of heat penetration test runs is important in order to obtain results which 
account for run‐to‐run, product, container and process variability.  
6.18.2.After initial cold spot determination tests are completed and all critical factors have been 
determined, at least two full replications of each test are recommended. Should results 
from these tests show variation, a minimum of a third test is recommended. 
6.18.3.Variation in the results is expected and quite common, especially for products which are 
non‐homogeneous or exhibit complex heating behavior. Variability is generally evaluated 
based on plots of the heating and cooling curves and/or lethality calculations and should 
be considered when identifying or predicting the slowest heating behavior of a process.

DATA ANALYSES 
 
6.19. Various methods are available for analyzing heat penetration data (4, 6, 7, and 8).  Regardless 
of the method used, awareness of the potential pros/cons for each method should be 
understood and addressed. 
 
RISKS, ISSUES AND OTHER CONSIDERATIONS 
 
6.20. Use of self‐contained (i.e., wireless data‐loggers) TMDs should be evaluated for accuracy, 
reliability, and applicability prior to use as the product temperature measuring devices for heat 
penetration studies.  In some cases these devices may provide benefits over using wired 
thermocouples, e.g., in agitating retorts such as continuous rotary sterilizers, batch retorts 
operated in an agitating mode, and hydrostatic retorts.   
6.21. Ecklund (5) reported correction factors for heat penetration data to compensate for errors 
associated with the use of non‐projecting, stainless steel receptacles. While not reported in the 
literature, this may also be a concern with other fittings. 
6.22. Type of Connectors and Associated Errors: Connectors used in a thermocouple circuit are 
fittings attached to a thermocouple within which electrical connections are made. Several types 
of connectors are available for specific applications and thermocouple type. Caution must be 
exercised to avoid certain sources of error which may be associated with the use of connectors 
and extension wires. These include: disparity between thermocouples, connectors and 
Issue Date: March 13, 2014 
Supersedes Date:  New     6‐7 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

extension wires; temperature differences between two wire junctions; and reversed polarity at 
the thermocouple‐extension wire junction. Thermocouple connectors should be cleaned 
frequently to remove oxidation from contacts to assure good electrical contact and prevent 
errors in thermocouple readings. Similar concerns should be addressed when using RTDs and 
thermistors. 
 
DOCUMENTATION 
 
The following provides a summary of details which may be incorporated in a checklist and 
documented in their entirety or partially as deemed appropriate for a specific study.  Other 
factors not listed in this section may also be relevant. 
 
6.23. Pre‐test Documentation 
6.23.1.Product characteristics 
6.23.2.Product name, form or style and packing medium 
6.23.3.Net weight and volume 
6.23.4.Consistency of viscosity of the liquid component 
6.23.5.Size, shape and weight of solid components 
6.23.6.Size of solid component clusters 
6.23.7.pH of solid and liquid components 
6.23.8.Methods of preparation prior to filling (ingredient mixing methods, special equipment, 
etc.) 
6.23.9.Matting tendency 
6.23.10.Rehydration of components 
6.23.11.Acidification procedures 
6.23.12.Other characteristics (e.g., % solids, density, etc.) 
6.24. Container Description 
6.24.1.Container material (brand name and manufacturer) 
6.24.2.Type, size and inside dimensions 
6.24.3.Container test identification code 
6.24.4.Maximum thickness (flexible container) 
6.24.5.Gross weight of container 
6.24.6.Container nesting characteristics 
6.24.7.Slowest heating or cold spot location in container 
6.25. Data Acquisition Equipment and Methodology 
6.25.1.Identification of data logging system 
6.25.2.TMDs and connector plug maintenance 
6.25.3.TMDs and connectors numbered 
6.25.4.Electrical ground checked (using thermocouples) 
6.25.5.Calibration of TMDs placed in heating medium  
6.25.6.Type, length, manufacturer and identification code of TMDs and connectors 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐8 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

6.25.7.TMD location in container 
6.25.8.Positioning technique for TMDs 
6.26. Fill Method 
6.26.1.Fill temperature of product 
6.26.2.Fill weight of product 
6.26.3.Headspace 
6.26.4.Filling method (comparison to commercial process) 
6.26.5.Sealing operations 
6.26.6.Type of sealing equipment 
6.26.7.Time, temperature, pressure and vacuum settings (if applicable0 
6.26.8.Gas evacuation method 
6.26.9.Can vacuum 
6.26.10.Volume of residual gases (i.e., flexible containers) 
6.27. Retort System 
6.27.1.Retort system – still or rotary, type of agitation (end‐over‐end, axial, oscillatory, none) 
6.27.2.Retort identification number 
6.27.3.Reel diameter (number of container positions) and rotational speed 
6.27.4.Heating medium (steam, steam/air, water immersion, water spray/cascade) and flow 
rate 
6.27.5.Circulation method for water or overpressure media 
6.27.6.Temperature distribution records 
6.27.7.Where applicable, heat transfer distribution records 
6.27.8.Retort venting schedule 
6.27.9.Package position study data for batch rotary retorts 
6.28. Loading of Retort 
6.28.1.Loading or racking system details 
6.28.2.Container orientation 
6.28.3.Location of thermocouples for retort temperature 
6.28.4.Use of ballast containers to ensure fully loaded retort (applicable to some retort systems) 
6.28.5.Selected time interval for data logging system 
6.28.6.Location of test containers in retort (slowest heating zone) 
6.29. Additional Information 
6.29.1.Date 
6.29.2.Test identification 
6.29.3.Processor and location 
6.29.4.Individual(s) performing heat penetration test 
 
6.30.Test‐Phase Documentation 
6.30.1.Test run identification 
6.30.2.Initial temperature of product at the start of heating 
6.30.3.Rotation speed (if applicable) 

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐9 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

6.30.4.Time heating starts 
6.30.5.Time vent closed and temperature, if applicable 
6.30.6.Time retort reaches set point temperature (tc) 
6.30.7.Temperature indicated on reference TID and when cook starts 
6.30.8.Pressure from a calibrated pressure gauge or transducer 
6.30.9.Time process begins 
6.30.10.Time cooling begins (pressure cooling, if applicable) 
6.30.11.Cooling water temperature 
6.30.12.Time cooling ends 
6.30.13.Any process irregularities or inconsistencies 
 
6.31.Post‐Test Documentation 
6.31.1.Container location and orientation 
6.31.2.Container net and gross weight check for leakage 
6.31.3.Thickness of container (flexible pouches) 
6.31.4.Measurement of container vacuum or residual air content (if applicable) 
6.31.5.Location of the TMD and whether or not it is impaled in a food particle 
6.31.6.Post‐processing product characteristics (e.g., syrup strength, appearance, viscosity, 
headspace, drained weight, pH, consistency, shrinkage, matting, clumping, etc.) 

   

Issue Date: March 13, 2014 
Supersedes Date:  New     6‐10 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

APPENDIX A – SELECTED BIBIOGRAPHY 

The following references represent a selection of publications that may provide more insight and 
information regarding thermal processing studies. 

   
1. Pflug, I. J and Berry M. R. 1987. Using Thermocouples to Measure Temperature during Retort or 
Autoclave Validation. J. Food Protection. Vol 50 (11): 975‐981.  
2. Tung, M. A and Britt, I. J. 1995. Food Material Science and Food Process Engineering: Keys to 
Product Quality and Safety.  Food Research International. Vol 28 (1): 101 – 108. 
3. Tung, M. A. Britt, I. J. and Ramaswamy, H. S. 1990. Food Sterilization in Steam/Air Retorts. Food 
Technology. 44(12) 105 ‐109. 
4. NFPA 1985.  Guidelines for Thermal Process Development for Foods Packaged in Flexible 
Containers.  National Food Processors Association, Washington, DC. 
5. Ecklund, O.F. 1956.  Correction factors for heat penetration thermocouples.  Food Technol.  
10(1): 43‐44. 
6. Pflug, I.J. 1975.  Procedures for Carrying Out a Heat Penetration Test and Analysis of the 
Resulting Data.  University of Minnesota, Minneapolis, MN. 
7. CFPRA 1977.  Guidelines for the Establishment of Scheduled Heat Processes for Low‐Acid Foods.  
Technical Manual No. 3.  Campden Food Preservation Research Association, Chipping Campden, 
Gloucestershire, UK. 
8. ASTM. 1988.  Standard Guide for Use in the Establishment of Thermal Processes for Foods 
Packaged in Flexible Containers.  F 1168‐88.  American Society for Testing and Materials, 
Philadelphia, PA. 
9. Bee, G.R. and Park, D.K.  1978.  Heat penetration measurement for thermal process design.  
Food Technol.  32(6): 56‐58. 
10. Ball, C.O. 1923. Thermal Process Time for Canned Food, Bulletin of the National Research 
Council, Washington, DC. Vol. 7, Part 1, Number 37. 
11. Ball, C.O. 1927. Theory and practice in processing. The Canner, 64 (5), 27. 
12. Ball C.O. and Olsen F.C.W. 1957. Sterilization in Food Technology. Theory, Practice and 
Calculation. New York, McGraw‐Hill Book Co. 
13. Jackson, J.M. and Olson, F.C.W.  1940.  Thermal processing of canned foods in tin containers. IV. 
Studies of the mechanisms of heat transfer within the container.  Food Research. 5(4): 409‐420. 
14. Niekamp, A., Unklesbay, K., Unklesbay, N., and Ellersieck, M.  1984. Thermal properties of 
bentonite‐water dispersions used for modelling foods. J. Food Science. 49(1): 28‐31. 
 

   

Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix  A‐1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

APPENDIX B ‐ Documenting Processing Equipment and Test Conditions Worksheet 

Where possible, drawings, schematics, pictures of the retort and associated equipment could be beneficial to include when documenting test 
retorts and test retort conditions. The following table is an example of a worksheet that may be used to document processing equipment and 
test conditions.  This example may be modified as needed. 

Survey Information 
Date ________________  Location _________________  Done by _____________________ 
 
Altitude ___________________  Height above sea level _____________________ 
 
TYPE OF RETORT 
’ Continuous Reel         ’ Hydrostat – Saturated Steam     ’ Batch – Steam/Air  ’ Batch – Water Spray   ’ Batch – Water Cascade 
 
’ Batch – Water Immersion  ’ Batch – Crateless   ’ Other (Describe) ___________________________ 
 
PRODUCT INFORMATION (optional) 
Product Name __________________________   
 
Product Heating ’ Simple, Convection   ’ Simple, Conduction  ’ Broken  ’ Other (describe) _______________ 
 
Container – Material ________  Dimensions _________  Orientation for processing ’ Vertical  ’ Horizontal  ’ Jumbled 
 
Fill/Net/Drained Weight _____________________ 
 
List product critical factors, targets, and limits _____________________________________________ 
PACKAGE INFORMATION (optional) 
Type of package ‐ ’ Rigid  ’ Semi‐Rigid  ’ Flexible  ’ Paperboard  ’ Other, describe ____________________________ 
 
Material of construction (describe) ‐ ______________________________________________________________ 
 
For metal cans ‐ ’ 2pc  ’ 3pc  Side seam construction ___________________________________ 
 
Loading Patterns ‐ ’ Jumble Pack  ’ Arrayed  ’ Other (describe) _____________________________________ 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Package Information, continued 
Seal/Closure – Type _______________ 
 
Container Vacuum ‐ ’ Yes  ’ No  If yes, allowed limits ___________________________________ 
 
RETORT OPERATION 
Throughput (CPM) ___________________________________   Containers/load _______________________ 
 
Cook Temperature Set‐point ________________  Pressure Set‐point during Cook ______________________ 
 
Rotation Set‐point _____________________________ 
 
Partial Loads  ’ Yes    ’ No  If yes, describe allowed conditions ________________________________________________________ 
 
___________________________________________________________________________________________________________ 
 
Where applicable, include retort control program. 
 
For Water Immersion ‐ ’ Full Immersion  ’ Partial Immersion  Water recirculation rate _________________ 
 
For Water Spray – Number and type of nozzles _______________________________  Flow Rate ___________________ 
 
For Water Cascade – Number and type of spreader/manifold _________________________  Flow Rate _______________ 
 
For Steam/Air – Fan location ___________________  Fan RPM _________________  Shroud ‐ ’ Yes  ’ No 
 
Pre‐heating of overpressure air/nitrogen ‐ ’ Yes  ’ No  If yes, describe how heated, how controlled, and to what temperature 
______________________________________________________________________________________________________ 
 
Steam/Air Ratio ___________________  Is venting part of the process ‐ ’ Yes  ’ No  If yes, when is vent closed _______________ 
 
LOADING CONSIDERATIONS (where possible secure drawings, schematics, pictures) 
 
Loading Configuration ‐ ’ Layered  ’ Nested  ’ Compartmented  ’ Offset  ’ Other (describe) _______________________________ 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Loading considerations, continued 
Water displacement requirements (ballast) _________________________________________________________________ 
 
Cassette, Basket, or Rack ‐ Dimensions _____________________  Distance between (if applicable) ______________________ 
 
Orientation in retort during processing _________________________  Percent open area ________________ 
 
Separator/Divider Trays – Material of construction ___________________________  Hole Size (if applicable) ________________ 
 
Percent open area ______________________________ 
 
Hole Open Area, Spacing and Pattern – Base plate ________________  Sides of cassettes/baskets/rack ___________________________ 
 
Separator/divider Sheets _________________________ 
RETORT SPECIFICS (where possible secure factory blueprints/schematics of the retort and all attendant piping as well as any alterations since the 
retort was installed) 
 
Manufacturer ________________________      Date Installed _______________    Physical Dimensions of shell ________________ 
 
Capacity – Continuous Reel:  Zone 1 _________  Zone 2 __________   Zone 3 _________   Zone 4 ________  Cooker _________ 
Cooler _________   Pressure Cooler __________  Total _________ 
 
Capacity – Hydrostatic: Preheat ______________  Sterilization ______________  Cooling _____________  Total __________ 
 
Number of flights ________________________ 
 
Capacity – Batch:  No. of Baskets/Crates per Retort ____________   No. of packages per load ________________ 
 
Capacity – Crateless:  Maximum number of containers per load __________________________________ 
 
Heat Transfer Medium:  ’ Saturated Steam   ’ Steam/Air   ’ Water  ’ Other _________________ 
 
Method of Heating Heat Transfer Medium (describe) ‐ _____________________________________________________ 
 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Retort specifics, continued 
Cooling Medium : ’ Ambient well water  ’ Chilled water  ’ Other (describe) ____________________________________ 
 
Method of process water microbial control _______________________________________________ 
 
Method of distributing/mixing heat transfer medium: ’ Fan  ’ Pump(s)  ’ Air plenum/shroud  ’ Nozzles  ’ Not Applicable 
 
’ Other (describe) _______________________________   
 
Controls (e.g., PLC, Computer Control, etc.) ‐ (Describe): 
_________________________________________________________________________________________ 
Note any differences between retorts in the test group. 
 
List of all controlling/sensing devices (note that ideally a schematic/drawing should be available): ___________________________ 
 
___________________________________________________________________________________________________________ 
 
Rotation:  ’ Yes  ’ No   Continuous Reel – RPM ___________________________   Hydrostatic – CPM ________________________ 
 
Batch – RPM _______________________________  Batch – Oscillatory _________________________ 
 
Vents – Type _________________________ Size ________________________  Location __________________________________ 
 
Pipe size and connection to drain headers or channels ____________________________________ 
 
Vent manifold/manifold header – Location __________________  Pipe size(s) including connecting pipes ______________________ 
 
Bleeders/Mufflers – Number __________  Size(s) _______________________ Location(s)__________________________________  
 
Construction _______________________________________________________________ 
 
Drains – Valve Type __________________  Valve Size ________________ Pipe size ___________  Pipe Length ______________ 
 
Connections to drain headers or channels ____________________________________ Location(s) ___________________________ 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Retort specifics, continued 
Condensate Removal System(s) – Type ________________________  Size _______________________  Location _______________ 
 
Check Valves ’ Yes  ’ No  If yes, Size ______________________  Type _____________________   Location(s) __________________ 
 
Safety Valves – Size __________________  Type __________________________  Location(s) _____________________________ 
 
Centering guides or baffles present  ’ Yes  ’ No  If yes, indicate location _____________________________________________ 
 
Water re‐circulation system (if applicable) – Pump type _____________  Pump Size ___________  Pump Capacity _______________   
 
Inlet/outlet port – Locations __________________  Size _______________  Filters _____________________  Recirculation line size _________ 
 
Flow meter (if applicable) – type __________________  Capacity ______________    
 
Horsepower _________   Pipe diameter for pump inlet ___________ and for pump outlet ____________ 
 
UTILITIES TO/FROM RETORT 
Steam  Supply 
Boiler Capacity ____________  Method of Firing ____________________  Pressure _______________ 
 
Steam header pressure (peak usage) _____________________  Pipe Size ______________  Length ___________________  
 
Steam header pressure (off‐load hour usage) _____________________ 
 
Steam injection chamber (if applicable) ________________________________  
 
Valve Type ___________  Valve Size ________________ 
 
Pipe fittings including steam by‐pass pipes from main line to retort (presence, type, size) _________________________________________ 
 
Size of all connecting steam pipes to the main line _________________________________________________________________________ 
 
Note all equipment using steam from same supply line ______________________________________________________________________ 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 5 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Utilities to/from retort, continued 
Pressure Reducing Valve/Regulator  ’ Yes   ’ No  If yes, type and pressure into retort _____________________________________________ 
 
Size and Type of Valve for Steam entry into Retort _____________________________________________________________________________
 
Steam distribution system in retort – Number, location and size of steam spreaders/distributors ______________________________________ 
 
Steam injection points – Size ___________  Type _______________________  Location(s) __________________________________ 
 
Steam spreader or nozzle – Shape ________________  Size ______________  Location(s) ________________________________ 
 
Configuration ___________________________  Number of _________________  Size and location in pipe _________________________ 
 
Size of “T” _____________________  Size of other pipe fittings __________________________________________ 
 
Water Supply (where possible, attach a P&ID) 
Water pressure to retort _______________________________________  Water temperature to retort _____________ 
 
Water distribution system in retort – Number, size and location of water spreaders/manifolds _______________________________________ 
 
_____________________________________________________________________________________________________________________ 
 
Process Water Supply – Source __________________  Quality ____________  Temperature _______  Controls (if any) ____________________ 
 
Cooling water supply – Source _____________  Quality ______________  Temperature _______ Controls (if any) ________________________ 
 
Method of heating processing water (describe) ____________________________________________________________ 
 
Heat exchanger – Size ______________  Type __________________ 
 
Pump – Size ________  Type __________  Location ____________________ 
 
Air/Nitrogen Supply 
Compressor Type ______________________________  Capacity __________________  Operating Pressure ____________________________ 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 6 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Utilities to/from retort, continued 
Filter Type ________________________  Filter Size ____________________  Dryer Type ___________________  Dryer Size ________________ 
 
Tank Type ______________________  Tank Size _______________________________ 
 
Line – Size ____________  Pressure ___________  Filters and dryers for instrument air _______________________________________________ 
 
Process air header – Line size _____________  Pressure _______________   Regulation (if applicable)  ________________ 
 
Entry – Location ______________________  Inlet Size _________________  
 
Control Valve – Size ____________________  Type ______________________  Pressure setting ____________  Flow rate _______________ 
 
Indicate availability to supply instruments _________________________________________________________________________________ 
 
Air heated  ’ Yes  ’ No  Indicate if air lines are in close proximity to steam or water lines ____________________________________________ 
 
For Overpressure – Pipe location(s) _______________  Pipe size ________________  Valve type ______________  Valve size ______________ 
 
Method of control (describe) ____________________________________________ 
 
SENSORS 
 
Temperature 
Type of Reference TID ____________________________  Model of TID _______________________  Location(s) _________________________ 
 
Range ______________________________  Response time __________________  Length of insertion _________________________ 
 
Length of scale (MIG) _______________________________   Increments (MIG) ___________________________________ 
 
Calibration status – Date last calibrated _________________  Next calibration date ______________________ 
 
Size, shape, location of wells ____________________________________________________________________________________________ 
 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 7 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Sensors, continued 
Temperature Control Sensing Device – Type __________________  Location _________________  Relationship to TID ____________________ 
 
For Water Spray and Water Cascade – Is this device in the water spray/cascade  ’ Yes  ’ No 
 
For Steam/Air – Is this device in the retort or in the air (return) plenum ‐ ’ Retort  ’ Air return/plenum 
 
Pressure 
Type of PID _________________________________  Model of PID ___________________________  Location(s) _________________________ 
 
Range ___________________________________  Calibration status – Date last calibrated _____________   
 
Next calibration date ____________________ 
 
Water 
Water level indicator type (if applicable) ____________________________________  Location(s) _______________________________ 
 
Other 
Rotation sensor Type __________________________   Location ____________________________  Drive system _____________________ 
 
Throughput/speed sensor Type ____________________________  Location ________________________ 
 
 
Type and size of flow meter _________________________________  Location(s) ______________________________ 
 
RECORDING DEVICES 
Recorder/Recorder Controller – Type _______________________  Resolution __________________________  
 
Parameters recorded _________________________________________  Calibration status ___________________________ 
 
List Process critical factors and their associated limits ‐ ___________________________________________________________________ 
 
________________________________________________________________________________________________________________ 
 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 8 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

WATER SPRAY AND WATER CASCADE RETORT – These are items that may not be covered in other areas of the survey. 
 
Water Spreader(s) – Type _____________  Size ________________  Location _________________________ 
 
Water recirculation system – Pump Type ______________  Pump Capacity ________________  Pump Impeller Size ______________ 
 
Pump Motor size ___________________   
 
Inlet/Outlet port Location ___________________   Size ______________________ 
 
Water flow rate ‐ ______________________________ 
 
Process water retention channel or trough in bottom of retort  ’ Yes  ’ No  If yes, Length ________  Width ______  Water depth ________ 
 
Process water retained for cooling ‐  ’ Yes  ’ No   
 
Process water retained for re‐use ‐  ’ Yes  ’ No 
 
Amount of process water at start of process ‐   ____________  Controlled by ____________________  Measured by  _____________________ 
 
Steam distributors (if applicable) – Location in relation to channel or trough ____________________________________________ 
 
Water Distribution Plate(s) – Water Cascade only – Inlet pipe to manifold location : ’ Top/center of retort shell  ’ Top/rear of retort shell 
 
Dimensions of manifold __________________________  Material of Construction ________________________________ 
 
Number of holes ____________  Size of holes __________  Location (hole pattern) ________________________________________________ 
 
Percent open area ________________________________ 
 
Water distribution pipes (Water Spray only) – Location of water inlet pipe to retort shell __________________________________________ 
 
Location of water distribution pipes in relation to circumference of interior of retort _______________________________________________ 
 
Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 9 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Water spray/cascade retorts, continued 
Length of pipes (do they extend length of shell) _______________________________________ 
 
Number of holes _____________  Size of holes __________________  Location of holes _____________________________ 
 
Nozzles – Type (if applicable) ___________________________  ’ Fixed  ’ Oscillatory  ’ Other (describe) _________________________ 
 
Restrict hole opening  ’ Yes  ’ No  If yes, how much ______________________________________________________ 
 
STEAM/AIR RETORTS –  
 
Air plenum and fan shroud – Distance (length) from retort shell to plenum if designed as a “shell in shell” ____________ 
 
If not designed as “shell in shell”, describe: _______________________________________________________________________ 
 
Fan shroud details (describe) _____________________________ 
 
 

Issue Date: March 13, 2014 
Supersedes Date:  New    Appendix B 10 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

APPENDIX C – Temperature Distribution Data Collection/Monitoring Points 

The following table is a compilation of suggested data collection/monitoring points when 
collecting temperature distribution data in different types of retorts. 
Retort Type
Data Collection/Monitoring Points  ST  SA  WS WC WI
Temperature and Pressure Controller set point(s), including if there is an 
(  (  (  (  ( 
overshoot set point for come‐up and a lower set point for processing 
Product or Ballast Initial Temperature.  (  (  (  ( (
Time process cycle starts, Time 0.  (  (  (  ( (
Time when the end of come‐up, start of thermal processing/cook step has been 
achieved, as indicated by either the step change in a control program or the 
(  (  (  (  ( 
achievement of process set‐point temperature at both the reference TID and the 
recorder/controller. 
Reference TID readings at sufficient intervals during the entire cycle, including the 
(  (  (  (  ( 
point in time it reaches the process temperature set point. 
Monitor rotation or agitation rate at sufficient intervals using an accurate 
calibrated stopwatch or calibrated device including any points where rotation rate 
(  (  (  (  ( 
changes during processing or on a continuous chart where rotation or agitation is 
used. 
Time at the end of thermal process and start of cool. (  (  (  ( (
Actual basket/crate/rack orientation in the retort. (  (  (  ( (
Operating activity of other retorts including the number of retorts entering come‐
(  (  (  (  ( 
up during the study. 
Numbers and descriptions of other equipment using steam (e.g., blanchers) at the 
(  (  (  (  ( 
time of the study and before, during, and after come‐up. 
Temperature of air supply entering the retort. (   
Water level in relation to spreaders and lowest level of containers in the retort. (  (  ( 
Time when the pressure set‐point(s) is achieved. (  (  ( (
Time and temperature when the drain is closed, if it is open during a portion of the 
(  (       
vent. 
Time and temperature, if or when the vent closes, taken from the reference TID. (  (   
Air flow in scfm or liters per minute, if applicable and available. (    (
Line steam pressure at the time of the test and before, during, and after come‐up, 
(  (       
if possible. 
Retort pressure, throughout the test cycle at sufficient intervals or on continuous 
  (  (  (  ( 
chart. 
Time steam bypass valve closes.  (     
Temperature of initial process water.    (  ( (
Flow or recirculation rate of water as determined by flow meter or other 
    (  (  ( 
acceptable means. 
Fill time (displacement) in those systems dropping water from a storage drum or 
        ( 
tank into the working processing vessel. 
Water level in process vessel in relation to the top surface of containers, stated as 
        ( 
a minimum or an actual level throughout the process. 
Line air pressure at the time of the test and before, during, and after come‐up, if 
        ( 
possible. 
ST – Saturated Steam   SA – Steam/Air   WS – Water Spray   WC – Water Cascade   

WI – Water Immersion   

Issue Date: March 13, 2014 
Supersedes Date:  New                                                                                                                 Appendix C 1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

APPENDIX D – Heat Penetration Documentation Checklist 

The following table is an example of a checklist that may be used for Heat Penetration Studies.  This example may be modified as 
needed. 

Pre‐Test Documentation 
Item/Parameter  Data  Done By 
Product characteristics     
Product name, form, style, packing medium     
Net weight and volume     
Consistency or viscosity of the liquid component     
Size, shape, and weight of solid components     
Size of solid component clusters     
pH of solid and liquid components     
Methods of preparation prior to filling (e.g., ingredient     
mixing methods, special equipment, etc.) 
Matting tendency     
Rehydration of components     
Acidification procedures     
Other characteristics (e.g., % solids, density, etc.)     

Container Description 
Container material (brand name and     
manufacturer) 
Type, Size, and Inside dimensions     
Container test identification code     
Maximum thickness (flexible     
container) 
Gross weight of container     
Container nesting characteristics     
Slowest heating or cold spot location     
in container 
Issue Date: March 13, 2014 
Supersedes Date:  New                                                                                                                Appendix D 1 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Data Acquisition Equipment and Methodology 
Identification of data logging system     
TMD type and where applicable,     
connector plug maintenance 
Type, length, manufacturer and     
identification code of TMDs and 
connectors 
Electrical ground checked (using     
thermocouples) 
Calibration of TMDs placed in     
heating medium 
TMD location in container     
Positioning technique for TMDs     

Fill Method 
Fill temperature of product     
Fill weight of product     
Headspace     
Filling method (comparison to     
commercial process) 
Sealing operations     
Type of sealing equipment     
Time, temperature, pressure, and     
vacuum setting (if applicable) 
Gas evacuation method     
Can vacuum     
Volume of residual gases (i.e.,     
flexible container) 

Issue Date: March 13, 2014 
Supersedes Date:  New                                                                                                                Appendix D 2 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Retort System 
Retort system – still or rotary, type     
of agitation (end‐over‐end, axial, 
oscillatory, none) 
Retort identification number     
Reel diameter (number of container     
positions) and rotational speed 
Heating medium (steam, steam/air,     
water immersion, water 
spray/cascade, hydrostatic) and flow 
rate 
Circulation method for water or     
overpressure media 
Temperature distribution records     
Heat transfer distribution records (if     
applicable) 
Retort venting schedule     
Package study position for batch     
retorts 

Loading of Retort 
Loading or racking system details     
Container orientation     
Location of TMDs for retort     
temperature 
Use of ballast containers to ensure     
fully loaded retort (applicable for 
some retort systems) 
Selected time interval for data     
logging system 
Location of test containers in retort     
Issue Date: March 13, 2014 
Supersedes Date:  New                                                                                                                Appendix D 3 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Additional Information 
Date     
Test identification     
Processor and location     

Individuals performing test     

Test Phase Documentation 
Test run identification     

Initial temperature of product at the     
start of heating 
Rotation speed (if applicable)     

Time heating starts     

Time vent closed and temperature, if     
applicable 
Time retort reaches set point     
temperature (tc) 
Temperature indicated on reference     
TID when cook starts 
Pressure from a calibrated pressure     
gauge or transducer 
Time process begins     
Cooling water temperature     
Time cooling begins (pressure     
cooling, if applicable) 
Time cooling ends     
Any process irregularities or     
inconsistencies 
Issue Date: March 13, 2014 
Supersedes Date:  New                                                                                                                Appendix D 4 
 
IFTPS Guidelines for Conducting Thermal Processing Studies 
 

Post‐Test Documentation 
Container location and orientation     
Container net and gross weight     
check for leakage 
Thickness of container (i.e., flexible     
pouches) 
Measurement of container vacuum     
or residual air content (if applicable) 
Location of the TMD and whether or     
not it is impaled in a food particle (if 
applicable) 
Post‐processing product     
characteristics (e.g., syrup strength, 
appearance, viscosity, etc.) 
 

Issue Date: March 13, 2014 
Supersedes Date:  New                                                                                                                Appendix D 5 
 
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

GUIDE1 TO INSPECTIONS OF
LOW ACID CANNED FOOD MANUFACTURERS
Part 3-Containers/Closures
TABLE OF CONTENTS Physical Examination ............................. pg. 15
Visual and Physical Examination Records
Introduction ..................................................... pg.1 ................................................................. pg. 16
Coding of Containers ..................................... pg. 2 References ...................................................... pg. 16
Empty Container Handling............................ pg. 2 Attachments.................................................... pg. 18
Container Closing ........................................... pg. 2
Metal Cans INTRODUCTION
Container Structure..................................... pg. 2
Double Seam Structure .............................. pg. 3 The Guide to Inspection of Low-Acid
Double Seam Formation ............................ pg. 3 Canned Foods consists of three separate
Seam Guidelines (Specifications) ............. pg. 4 documents; Part 1 covers Administrative
Seamer Maintenance and Adjustment..... pg. 4 Procedures\Scheduled Processes; Part 2 covers
Container Defects ........................................ pg. 5 Manufacturing Procedures/Processes and Part 3
Double Seam Evaluation Requirements covers Container/Closures. In addition to providing
Visual Seam Examination ...................... pg. 6 guidance for inspections of low acid canned foods
Double Seam Examination .................... pg. 7 (LACF) manufacturers, the guide(s) also contains
Visual and Double Seam Examination background and general information on LACF
Records .................................................... pg. 7 regulations and procedures.
Post Process Container Handling ................. pg. 8 In addition to the information and
Glass Jars instructions provided in IOM Subchapter 530,
Container Structure 21CFR 108 and 113, and applicable compliance
Glass Container ....................................... pg. 8 programs, direct attention to areas covered in this
Metal Closure ........................................... pg. 8 Guide when covering LACF manufacturers.
Vacuum Formation ..................................... pg. 9 Another good reference is the Food Processors
Vacuum Closures ........................................ pg. 10 Institute 'Canned Foods' manual, which should be
Closure Evaluation Requirements available from anyone in your district who has
Visual Examination ................................. pg. 10 attended a Better Process Control School.
Physical Examination .............................. pg. 11 At the current time DEIO has available, for
Visual and Physical Examination Records loan only, the following NFPA manuals:
................................................................... pg. 12
Other Quality Control Equipment ............ pg. 12 1. Thermal Processes For Low-Acid Foods in
Retortable Pouch Metal Containers (NFPA Bulletin 26-L, 13th
Container Structure and Sealing Method. Pg. 12 Edition)
Critical Factors in Sealing........................... Pg. 13 2. Thermal Processes For Low-Acid Foods in
Semirigid Trays and Bowls Glass Containers (Bulletin 30-L)
Sealing Method ........................................... pg. 13 3. Flexible Package Integrity Bulletin (Bulletin
Critical Factors in Sealing........................... pg. 13 41-L)
Container Defects- 4. Guidelines for Thermal Process
Pouches/Semirigid Containers/Heat Sealed Development for Foods Packaged in
Packages ......................................................... pg. 13 Flexible Containers
Seam Evaluation Requirements ................ pg. 14 5. Continuous Rotary Sterilizers-Design and
Visual Seam Examination ..................... pg. 14 Operation (Bulletin 44-L)

1
Note: This document is reference material for investigators and other FDA personnel. The document does not bind FDA and does not
confer any rights, privileges, benefits or immunities for or on any person(s).

1
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

6. Automatic Control Guidelines For Aseptic has a program and/or procedure for handling and
System Manufacturers and Companies inspecting incoming containers and if the program
Using Aseptic Processing and Packaging is followed. Also, inspect empty containers prior to
for Preserving Foods (Bulletin 43L) filling for damage that may result in container
defects. Any damage should be noted, and follow-
DEIO also has a supply of Institute for up visual examination of finished containers should
Thermal Processing Specialists (IFTPS), 'Protocol be performed to determine if the damage caused
for Carrying Out Heat Penetration Studies'. defects in the containers. Evidence of container
The AOAC Chart "Classification of Visible damage causing defects in the finished containers
Can Defects (Exterior)" is helpful when performing should be reported on the FDA-483 if no corrective
field exams. Districts should have this chart actions had been taken by the firm on the affected
available (usually the labs have them). lots. (Reference individual container type sections
The sampling schedule for canned and of this guide for definitions and discussion of
acidified foods is in the Investigations Operations container defects.)
Manual and the Guide to Inspections of Low Acid Empty containers (except pouches) should
Canned Food Manufacturers , Part 2 be inverted and cleaned prior to fill. Typically
containers are cleaned using vacuum, air, or a
CODING OF CONTAINERS water spray to remove possible foreign material
prior to filling.
See Guide to Inspections of Low Acid
Canned Food Manufacturers Part 2, pg. 46. CONTAINER CLOSING:
EMPTY CONTAINER HANDLING: After filling the container, a can cover (end
or lid) is placed onto the container and seamed.
Empty containers for low acid canned food The closing operation is what produces a hermetic
processing are typically received in bulk quantities, seal; i.e., a seal designed to be secure against the
packaged to avoid container damage in transit, by entry of microorganisms. For cans, to secure the
the food manufacturer. For example, metal cans hermetic seal an appropriate sealing compound is
are typically received on pallets with a cardboard applied to the inside of metal can ends at the curl;
divider between each can layer or nested in paper and for glass jars the sealing compound is applied
sleeves on pallets; glass jars are received in boxes to the metal closures during container lid
with separate compartments for each jar; plastic manufacturing. It is very important that the seam
bowls and cups are received nested in cardboard is adequate to prevent entry of microorganisms. A
boxes; and empty pouches are received securely brief description of the different container types
packed in cardboard boxes. and closing operations for these container types is
It is important that empty containers are as follows:
handled during receipt and processing in a manner
that precludes container damage. For example, if METAL CANS
the flange of a metal can is damaged during
shipment, receipt, or filling, it can result in a can
seam defect. Therefore, it is important that the
Container Structure:
LACF manufacturer has a program for inspecting The container structures that help form and
incoming containers for defects prior to the filling become a part of the finished double seam are the
operation. This inspection program should include body flange and the end curl (refer to Attachment
a visual examination and when appropriate, a tear 1). Attachment 1 also illustrates and defines double
down examination for defects that could affect seam terminology:
product and/or package integrity. Incoming Flange: The flange is the edge of the body
container inspection programs range from a small cylinder that is flared outward resulting in a rim or
manufacturer checking every container before ledge. The flange is formed into the body hook
filling, to large manufacturers that may follow a during double seaming and becomes interlocked
statistically valid sampling plan (e.g., mil-standard with the cover hook. The width and radius of the
105E) to inspect their incoming containers for flange are determined by the container
defects. manufacturer and are designed to form a proper
During the inspection determine if the firm body hook when using the container

2
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

manufacturer's specifications for the double accompanying wrinkles around the seam. The
seaming operations. second operation in the formation of the double
End Curl: The end curl is the extreme edge seam presses the body and cover hooks together
of the can end (cover) that is turned inward after to such a degree that the wrinkles should be ironed
the end is formed. It is the structure used to form out sufficiently to ensure a hermetic seal.
the cover hook and is designed to provide sufficient In a completed double seam, any
metal and proper contour for a good cover hook, remaining wrinkles help to indicate double seam
and easy feeding of end units into the closing tightness. Tightness rating is a numerical
machine. designation which indicates the relative freedom
from wrinkles or % smoothness of the cover hook.
Double Seam Structure: Refer to Attachment 3.
The double seam structure is judged by After the coverhook is removed, the can
measurement and evaluation of specific body should be examined for body wall impression
components comprising the seam. These or what is commonly referred to as pressure ridge.
measurements are based on guidelines provided This impression is caused by the seaming roll
by the container manufacturer to the low-acid pressure during the seaming operation. Visual
canned food manufacturer to assist in maintaining inspection of the pressure ridge provides additional
acceptable seams during production. The final assurance of the tightness of the can seal. The
evaluation of the double seam can only be made body wall impression or pressure ridge should be
by a visual inspection of the torn down seam in visible and complete around the inside periphery of
conjunction with the measurements. The seam the can body where the coverhook was removed.
measurements that can be performed to evaluate Refer to Attachment 4.
the double seam are as follows (refer to
Attachment 2): Double Seam Formation:
Countersink: The countersink is the The seal for the metal can is made in two
distance measured from the top of the double operations, hence the term "double seam". The
seam to the end panel adjacent to the inside wall of can seamer (or closing machine) has four basic
the double seam. parts that are directly involved in forming the
Seam thickness: Seam thickness is the double seam. These parts are:
maximum dimension measured across or
perpendicular to the layers of material in the seam. 1. Seaming Chuck: A flat round plate which
This measurement is one, but not the only fits inside the can cover and supports the can
indication of the tightness of the double seam. against the seaming rolls.
Seam width (length or height): Seam width 2. Can Lifter or Base Plate: a round plate
(also referred to as seam length or seam height) is which lifts the can and can end to the seaming
the dimension measured from the top to the chuck and applies upward pressure during the
bottom of the double seam (parallel to the hooks of seaming cycle.
the seam). 3. First Operation Seaming Roll: A roller
Body and cover hook: These are internal adjacent to the seaming chuck that has a deep,
measurements. As previously referenced the body narrow groove (forming tool).
hook is formed from the body flange, and the cover 4. Second Operation Seaming Roll: A roller
hook is formed from the end curl during the double adjacent to the seaming chuck with a wide and
seaming operation. These structures, observed in shallow groove (tightening, flattening tool).
a cross section, have an interlocking relationship to These four basic parts of the can seamer
each other. are adjustable, and precise adjustment is critical in
Overlap: The degree or length of interlock obtaining a well formed double seam.
between the body hook and cover hook is known
as overlap. The double seaming operation is a form of
Tightness: Seam tightness is judged by the metal spinning. The sequence of steps in the two-
degree of wrinkling at the end of the cover hook. seaming-roll operation is as follows:
During double seam formation, the cover curl is 1. Either the can is placed on the can lifter
guided around and up under the body flange. This (base plate) and the cover is automatically placed
crowds the cut edge of the curl into a smaller on the can; the can cover is placed on the can as it
circumference, resulting in a wavy cut edge with moves onto the can lifter; or if the cover is placed

3
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

on the can during the clinching operation, the can base plate should be sufficient to force the cover
with the cover is placed on the can lifter. right onto the chuck and hold the can firmly in
contact. The first operation seaming roll then
2. The base plate raises the can and cover engages the cover and curls the cover curl (which
onto the seaming chuck tightly clamping the cover becomes the cover hook) into the flange of the
onto the can. body which then becomes the body hook in the
3. The first operation seaming roll(s) is finished seam. In a good or normal first operation
brought into contact with the can and cover, and roll, the cover hook is rounded at the bottom and is
the metal spinning groove forms the first operation in contact with the body of the can. The ends of
seam. The first operation seam can be defined as the cover hook and body hook are essentially
curling the cover (end) hook around the inside of parallel. There should be no curvature in the
the body hook to form a loose interlock of the can extremities of the cover and body hooks. Refer to
end and can body. Attachment 11.
4. The second operation seaming roll(s) is
brought into contact with the can and cover, and Second Operation Seaming:
the metal spinning groove forms the second The second operation roll has a shallow
operation seam. The second operation seaming and flat profile in comparison to the narrow and
roll flattens the seam and seals the can. deep groove profile of the first operation roll. The
second operation roll flattens the fold resulting
Attachment 5 illustrates the sequence of from the first operation and presses the folds
operation in seaming a can end onto a can body. together tightly enough to compress and force the
Attachment 1 illustrates a completed double seam sealing to flow into the seam voids. Refer to
and details double seam terminology. Attachment 6.

Can double seamers are generally of two Seam Guidelines (Specifications)::

types: Can seam guidelines (specifications) are
The can spin type: The seaming rolls are provided to the low acid canned food manufacturer
stationary and the can spins as it is held between by the supplier of the container and end being
the base plate and the seaming chuck. In this type used. The guidelines detail the measurements, in
of seamer the base plate and chuck both spin at a thousands of an inch, of each attribute of the
high rate of speed while the stationary rolls swing double seam for both the first and second seaming
in to make contact with the can and cover and then operations. They also provide a set-up aim or ideal
swing back out after the seaming operations are starting dimensions for the set up of the seamer.
complete. The operating limits set the range for good
The can stationary type: The can, base practice. Attachment 7 provides an example of a
plate and chuck are all stationary and one or two seam guideline.
first and second operation seaming rolls roll It is extremely important to understand that
around the stationary can forming the double seam guidelines by themselves cannot be used for
seam. determining the quality of a double seam. The
With either type of double seamer, a can seam guidelines are to be used in setting up the
may be placed by hand onto the base plate, or fed double seams initially and maintaining seam
mechanically onto the base plate in the seamer. integrity during production. Final acceptability of
the double seam should be based on total
First Operation Seaming evaluation of the seam by a qualified person and
The first roll seaming operation is the most not on dimensions alone. Good seaming practice
critical part in the formation of a good seam. The requires constant visual examination, frequently
second roll seaming operation simply flattens the scheduled tear-down evaluation, machine
closure fold made during the first roll seaming maintenance, and immediate correction of
operation; so deficiencies in the first seaming roll unacceptable conditions.
operation cannot be corrected during the second Since seam guidelines will vary depending
roll seaming operation. on the source of the container (i.e., Crown Cork &
The first operation roll has a narrow and Seal, Ball, Siligan, etc.), the guidelines should
deep groove profile. The body hook and cover always be provided by the container manufacturer.
hook are determined by the first operation roll and If the LACF manufacturer cannot provide a copy of
the base plate pressure. Upward pressure on the

4
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

the appropriate seam guidelines, they have nothing measurement or tightness rating evaluation are
on which to evaluate the double seam. This can be below the minimum guidelines a resample from
listed as an objectionable condition on the FDA- the questionable seaming station should be made.
483. If the resample continues to show out-of-guideline
measurements in overlap and/or wrinkle the
Seamer Maintenance and Adjustment : machine should be stopped and adjusted.
It is important that the LACF manufacturer A LACF manufacturer should have
has in place a preventative maintenance program experienced, competent personnel to adjust the
for the seamer. Under normal use conditions, the seamer and evaluate double seams.
seaming rolls, bearings, base plate, chuck etc. can
become worn resulting in the possibility of
defective double seams. Seaming rolls are Container Defects - Metal Cans:
evaluated and changed routinely because they Container defects are seam abnormalities
wear during production, thus altering the groove that are generally serious and may result in the loss
profiles. For example, a badly worn first operation of the hermetic seal. Following is a description of
roll can result in a loose first operation seam and some of the more common container defects:
when a normal second operation roll pressure is Droop (Refer to Attachment 8): A droop is a
applied, can cause droops (see Attachment # 8) in smooth projection of a double seam below the
the finished double seam. bottom of a normal seam. The droop may occur at
any point of the double seam. If the container has
Adjustment of Closing Machine to Correct Out-Of- a side seam it is common to have a slight droop
Guideline Measurements and/or Defective Seams: where the double seam crosses over the lap of the
Whenever the set-up aim or operating limit side seam. This area of cross over is referred to as
checks indicate that seams are not meeting the the "juncture". A slight droop at the juncture may
guidelines or when an obvious seam defect is be considered normal, however, if the droop is
found on visual inspection, the manufacturer must excessive the overlap may be too short or non-
know what steps to take to correct the condition. existent. Some possible causes of droops are
The FDA investigator must also be aware of listed in Attachment 8.
seaming conditions that could result in container Vee or Lip (Refer to Attachment 8): "Vees"
defects in order to evaluate whether the firm took or "lips" are projections of the double seam below
the appropriate corrective action. Evaluation of the the bottom of a normal seam that resemble a "V"
firm's actions are made through review of their shape. There is usually no overlap of the cover
container records. Container records will be hook with the body hook and these defects usually
discussed later in this section. occur in small areas of the seam. The probable
If an obvious and recurring can seam defect causes for "vees" or "lips" is the same as for
is found on visual inspection and in a second "droop".
sample, it usually signifies that some mechanical Sharp seam (Refer to Attachment 9): A
fault has developed and the production line should "sharp seam" refers to a sharp edge at the top
be stopped in order to take corrective action. inside portion of the seam. Usually a sharp seam is
Product from previous production that may have noticeable at the side seam juncture in a three
been affected should also be isolated. piece container, however, a sharp seam can be felt
The most critical attributes to consider in at any point along the inside top of the seam. The
judging the quality of the double seam are overlap sharp seam is caused by a portion of the end
and tightness (wrinkle). If one of the can seam (cover) being forced over the top of the seaming
measurements (i.e. body hook) is slightly beyond chuck during double seaming. A sharp seam can
the specified guidelines but the rest of the seam is usually be felt more easily than seen. A sharp
evaluated and the overlap and tightness (wrinkle) seam can be the first indication of a more serious
are within specified guidelines, then adjustments to defect known as a cut-over.
the seamer can be made at the next scheduled Cut-over (Refer to Attachment 9): A "cut-
shut-down. In this instance, the manufacturer over" is a seam defect where the top of the inside
should identify the out-of-guideline measurement portion of the seam has become sharp enough to
and document they have evaluated the rest of the fracture the metal. As in the definition of "sharp
double seam, but did not find immediate corrective seam", this condition usually occurs at the side
action necessary. However, if overlap seam juncture of a three piece container. Some

5
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

possible causes of both sharp seams and cut-overs out of square causing an unevenness at the lap or
are listed on Attachment 9. juncture in three piece cans.
Jumped seam or Jump over (Refer to Cut seam (Refer to Attachment 13): A "cut
Attachment 10): A jumped seam or jump-over is a seam" is a fractured double seam where the outer
portion of the double seam which is not rolled tight layer (cover hook) of the double seam is fractured.
enough. This defect occurs adjacent to the side Possible causes are listed on attachment 13.
seam or juncture area in a three piece container Fractured embossed codes: "Fractured
and is caused by the seaming rolls jumping at the embossed codes" are fractures through the metal
juncture. Wrinkles will be left in the coverhook at end of the can at the code mark. Possible causes
the point where the rolls jumped. During for the fractured metal are:
examination of the seams the area immediately 1. Mis-alignment of male and female
adjacent to either side of the juncture should be coding dies.
carefully inspected for excessive wrinkle. Possible 2. Intermixing of new and old type code
causes of a jumped seam are listed on Attachment characters.
10. 3. Improper matching of male and female
Deadhead or spinner (Refer to Attachment type code characters.
11): A deadhead or spinner (also referred to as slips 4. Too deep a code mark.
or skids) is an incomplete seam caused by the
chuck spinning in the countersink during the Broken chuck: A "broken chuck" defect
seaming operation. Some causes of deadheads occurs when a portion of the seaming chuck lip has
are listed on Attachment 11. broken and results in an excessively loose seam at
Mis-assembly: A "mis-assembly" is the the broken part due to a lack of backup support for
result of the can body and the can end having been the seaming roll. Possible causes are:
improperly aligned in the closing machine. 1. Severe jam in the closing machine.
Therefore, the seam is completely disconnected 2. Seaming rolls binding on chuck.
partway around the can. The most common cause 3. Metal fatigue in chuck lip.
of a mis-assembly is incorrect closing machine 4. Prying against the seaming chuck to
timing or settings. clear a jam.
False seam (Refer to Attachment 12): A
"false seam" is a seam or portion of the seam FDA, in cooperation with the Association of
which is completely unhooked, and in which the Official Analytical Chemists, published a brochure
folded cover hook is compressed against the folded titled "Classification of Visible Can Defects". The
body hook. A false seam is not always detectable brochure defines metal can defects in three
in an external examination. Some causes of false categories. They are:
seams are listed on Attachment 12. 1. Critical: Defects which provide evidence that the
There are other terms that more specifically container has lost its hermetic seal (e.g., holes,
describe a false seam condition. They are: fracture, puncture etc.)
Knocked down flange: which is usually 2. Major: Defects that result in cans which do not
caused by a bent can flange before double show visible signs of having lost their hermetic
seaming. seal, but are of such magnitude that they may have
Damaged end curl: is a defect resulting lost their hermetic seal.
when the end curl is flattened in one or more spots, 3. Minor: Defects which have had no adverse effect
causing the curl to fold back on itself. This is on the hermetic seal.
usually caused by handling damage to ends or The brochure also provides a pictorial of
improper cover feed. can seam defects and rates the defects as critical,
Can body buckling: The can body directly major and minor. If you cannot locate a copy of
under the double seam is buckled or twisted. this brochure in your district, contact your servicing
Possible causes are: lab.
1. Excessive baseplate pressure
2. Improper pin-gauge height (distance Double Seam Evaluation Requirements:
between base plate and chuck)
Visual Seam Examination (Non-Destructive Test):
Cocked body (Refer to Attachment 12): A 21 CFR Part 113.60(a) requires a visual
"cocked body" is a can manufacturing defect. It examination of at least 1 can per seaming head by
occurs when the can body blank is manufactured

6
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

a qualified container closure inspector at intervals "micrometer" method or the "optical" method.
of sufficient frequency. The regulation requires If the processor is using the micrometer
that double seamed containers be visually method the regulation requires that 3
inspected for gross closure defects such as sharp measurements are taken at points approximately
seams, cut-overs, deadheads, false seams, droops 1200 apart around the double seam. On 3 piece
and broken chuck. The frequency of the visual cans the first measurement can be taken directly
examination should be made at intervals not to across from the side seam and the next two
exceed 30 minutes (of operational time); and measurements are then taken 1200 to either side of
additional visual examinations must be performed the first measurement. On 3 piece cans the
immediately following a jam in a closing machine, measurements must be taken at least one-half inch
after closing machine adjustment, or after startup from the side seam juncture as the juncture may
of a machine following a prolonged shut-down. An interfere with a true seam measurement.
example of a prolonged shut down may be when Micrometer measurements are made and
the plant ceases production at 6:00 PM and restarts recorded in thousandths of an inch. The high and
production at 8:00 AM the next day. low measurements are recorded on the double
seam teardown examination record. If the
manufacturer is using the micrometer method the
Double Seam Teardown Examination required
Requirements (Destructive Test):
The double seam teardown examination is measurements are:
a destructive test. Tools that are used to perform Cover hook length
this test include a seam micrometer, countersink Body hook length
gauge, can opener and nippers. Optional Width (also referred to as length or height)
equipment for seam teardown examinations Tightness (by observation for wrinkle)
include a seam saw, seam projector and seam Thickness
scope. Although it is not imperative the
investigator carry this equipment to each LACF Optional measurements are:
inspection, it is very important that they know how Overlap (by calculation)
to operate this equipment and read measurements Countersink
from the micrometer, seam projector or seam
scope. It is also important that the investigator The regulation specifies the formula used to
know how to determine the tightness or wrinkle calculate overlap when micrometer measurements
rating of the cover hook. Knowledge of the are used:
procedures used to perform double seam teardown
examination are essential to evaluating the firm's CH + BH + T (.010in)* - W, where
knowledge and ability to do this examination. CH = cover hook
Attachment 14 explains the procedure for using a BH = body hook
seam projector for examining a cross section of the T = cover thickness *(general
seam. Attachment 15 explains the can seam practice use .010 inches for tin plate
micrometer and procedure for use, and Attachment thickness)
16 explains the use of a seamscope for the same W = width
exam.
The requirements for double seam Measurements used to calculate the
examinations are specified in 21 CFR Part overlap should not be averaged. In fact, the lowest
113.60(a)(1). The regulation states that teardown values should be used to determine the worst case
examinations shall be performed by a trained scenario. For example, to calculate the worst case
closure technician at intervals of sufficient scenario you should use the lowest measurements
frequency to ensure proper closure. The teardown for CH and BH and the highest measurements for
examinations shall be made on the packer's end W.
double seams on at least 1 can from each seaming
head to ensure maintenance of seam integrity. If a seam scope or seam projector is used
Sufficient frequency is defined in the regulation as (optical method) to make the seam measurements,
intervals not to exceed 4 hours (operational time). the required measurements are:
The regulation allows for 2 different Body hook length
methods of double seam examination; the Overlap

7
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

Tightness (observation for wrinkle) next scheduled break in the production period.
Thickness (determined by Some examples under which processing
micrometer measurement if the could continue with little risk to the product are:
optical instrument cannot read this 1 . If visual inspection indicates a slight sharpness,
value) especially in the junction area.
2. If the container guidelines require body hook
Optional measurements are: measurements in the range of .072" - .088" and 1
Width (also referred to as length or measurement was taken and recorded as .071 for a
height) low and .076 for a high. All other measurements
Cover hook are within guidelines including overlap, wrinkle,
counter sink and pressure ridge.
3. When the thickness guidelines require a range
Visual Seam and Double Seam Teardown of .046" to .052" and measurements show thickness
Examination Record Requirements: up to .053", but the cover hook displays a 100%
The regulations require that the wrinkle (tightness) rating. Refer to Attachment 3.
results of visual seam and double seam teardown Some examples under which processing
examinations along with any corrective action should be shut down and corrective action taken
taken shall be recorded. 21CFR Part 113.100(c) are:
details 1. During visual seam examination a cut-over is
found around the periphery of the inside of the
the minimum requirements for visual and double seam.
seam examination records as follows: "Written 2. During visual seam examination and on a repeat
records of all container closure examinations shall sample, vees or lips are found protruding below
specify the product code, the date and time of the bottom of the double seam.
container closure inspection, the measurements 3. Evidence of skidding or deadheading.
obtained, and all corrective actions taken." Records 4. During both initial and repeat teardown
must be signed or initialed by the container closure examination on one seaming head, calculated
inspector and reviewed by management with overlap is below the minimum guideline
sufficient frequency to ensure that the containers requirement.
are hermetically sealed.
Sufficient frequency can be defined as, at Good seam formation cannot be judged
least prior to shipment of the product. However, solely by mechanical means or measurements.
FDA investigators should encourage LACF The evaluation of good double seams requires
processors to review the container records at the experience and skill. This is why it's important for
same time as the thermal processing records; or a firm to have experienced and well trained can
not later than 1 working day after the process, and seam mechanics. If observations indicate the
prior to shipment of the product. individual(s) performing can seam examinations
Attachment 17 and 18 respectively, are lack adequate training or skills this should be
examples of a visual examination record and discussed with plant management.
double seam teardown examination records.
When reviewing visual and double seam
examination records it is important the investigator Post Process Container Handling
knows how to interpret the information provided See Guide to Inspections of Low Acid
on the records. For example, if a visual or Canned Food Manufacturers, Part 2, pg. 44.
teardown examination found a defective container
or measurements outside of guidelines, the
processor should have taken a repeat sample from
Glass Jars:
the questionable seaming station to evaluate
before any machine adjustments are attempted. If Container Structure:
the repeat sample shows the same defect or out of
guideline measurement then the processor will Glass container:
have to determine whether the nature of the defect There are 3 basic parts to a glass container
is of sufficient magnitude to warrant immediate (Refer to Attachment 19):
shut down of the production line to make
adjustments, or to continue processing until the 1 . Finish: The finish is the very top part of the jar

8
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

that contains threads or lugs that contact and hold

the cap or closure. Specific areas identified in the Vacuum Formation:
"finish" are sealing surface, glass lug, continuous Almost all low-acid foods packaged in glass
thread, transfer bead, vertical neck ring seam and containers are sealed with vacuum-type closures.
the neck ring parting line. The vacuum within the package and the
overpressure in the retort on the outside of the cap
2. Body: The body of the container is that portion play an important role in forming and maintaining
which is made in the "body mold". It is the largest a good seal. There are two basic types of cappers
part of the container and lies between the finish which apply caps while forming a vacuum in the
and the bottom. The characteristic parts of the container:
"body" are the shoulder, heel, side wall, and mold 1. Mechanical Vacuum Capper: applies the cap to
seam. the jar in an evacuated chamber (usually used on
dry products and rarely on low-acid processed
3. Bottom: The bottom of the container is made in foods).
the "bottom plate" part of the glass-container mold.
The designated parts of the bottom area are 2. Steam Flow Capper: the container is subjected
normally the bottom plate parting line and the to a controlled steam flow that displaces the
bearing surface. headspace gases from the jar by a flushing action.
The steam is trapped in the headspace as the cap is
Metal closure: applied, then condenses to form a vacuum which
Among the terms commonly used for helps hold the closure in place.
describing parts of metal vacuum closures are the
following (Refer to Attachment 19): There are four primary factors that affect
Face: The outside of the cap vacuum formation (however, 1-3 are considered
Reverse: The inside of the cap critical factors only if designated critical by the
Panel: The flat center area in the top of the process authority):
cap. 1. Headspace: There must be sufficient void or
Radius/Shoulder: The rounded area at the headspace at the top of the container to allow
outer edge of the panel connecting the panel and adequate steam to be trapped in the container for
skirt. forming a vacuum, and to accommodate product
Skirt: The flat side of the cap. The skirt expansion during retorting. The correct amount of
may be smooth, knurled, or fluted and serves as headspace varies with products, processes, and
the gripping surface. package design, but a rule-of-thumb in the industry
Curl: The rounded portion at the bottom of is that it should be not less than 6% of the
the skirt that adds rigidity to the cap and serves to container volume. Inadequate headspace can
protect the cut edge of the metal. result in displacement or deformation of the
Lug: A horizontal inward protrusion from closure during retorting.
the curl that seat under the thread or lug on the
finish of the glass container and holds the cap in 2. Product fill/sealing temperature: Product filling
position. temperature affects the final vacuum in the
Coatings: Coatings and inks used on the container (due to product contraction upon
inner and outer surfaces of the cap to protect the cooling). The higher the product temperature at
metal from attack, adhere gasket materials, and the time of sealing, the higher the final package
decorate the closure. vacuum. Higher filling temperatures also result in
Gasket: The actual sealing member of the less air being entrapped in the product.
cap which must make intimate contact with the
glass finish at the proper point to form an effective 3. Residual air in the product: Air can have a direct
seal. Gaskets are made of either rubber or effect on the final package vacuum and should be
plastisols. kept at a minimum for good sealing. The more air
Safety Button or Flip Panel: A raised, that is trapped in the product, the lower the
circular area in the center of the panel which is vacuum. Expansion of residual air in the container
used only for vacuum packed products and serves during processing can exert pressure against the
two principle purposes which are detection of low closure and adversely affect seal integrity. Air in
or no vacuum packages and an indicator to the the container can also impede heat penetration into
consumer of a properly sealed package.

9
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

the container during retorting. the most important.

2. Press on-Twist off (PT) closures: This closure is
4. Capper vacuum efficiency: Capper vacuum in widespread use on baby foods as well as other
efficiency refers to the ability of a steam flow products. Structurally, the PT cap consists of a
capper to produce a vacuum in sealed glass steel shell with no lugs. The gasket is molded
containers. The most convenient, routine check on plastisol on the inside vertical wall and covers a
the vacuum efficiency of a steam-flow capper is the sealing area extending from the outer edge of the
"cold-water vacuum check." This measurement is top panel to the curl of the cap. These closures
required by 21CFR 113.60(a)(2), and must be typically have a safety button or flip panel.
performed before actual filling operations, and The cap is first heated to soften the
results must be recorded. plastisol. It is then pushed directly down on the
The method of cold-water vacuum check glass finish after air is swept from the headspace
requires a series of jars to be filled with cold tap with steam. The glass threads form impressions in
water to the approximate headspace that will be the skirt of the cap gasket and allow the cap to be
maintained with the product to be run. A series cammed-off and on. The PT closure is held in place
means 4 to 6 containers for a straight-line capper, on the finish primarily by vacuum, with some
and 1 container for each capping head on a rotary assistance from the thread impressions in the
capper. The capper is allowed to warm up to gasket wall when the cap is cooled.
operating temperature and normal steam setting 3. Plastisol-Lined Continuous Thread (PLCT) Cap:
and these jars are then sealed in the capper. The The PLCT cap consists of a metal shell with a
jars are then opened and re-run through the capper threaded skirt curled at the end. It contains a
and then checked for vacuum. By running the jars flowed-in plastisol gasket on the inside that makes
through the capper the first time the water is de- intimate contact with the top of the finish when the
aerated, and thus a truer vacuum reading is cap is screwed onto the jar finish. The PLCT cap
obtained after the second run. Vacuum is may be used in both steam and non-steam
measured using a standard vacuum gage. The applications. Security measurements on this type
range of vacuum is recommended by the container of container closure can be performed. However,
manufacturer, but typically should be 22 inches or pull-up cannot be determined.
more.
Closure Evaluation Requirements:
Generally closure application inspections
Vacuum Closures: are performed either visually (non-destructive), or
Currently, two primary types of vacuum by cap removal (destructive). It is important to
closures are used on low-acid food products (refer know the tests and observations on the different
to Attachment 20): types of closures as well as the defects that can
1. Lug type closure: This closure is the occur (refer to Attachment 21).
predominate vacuum-cap type. It is a convenient
closure because it can be removed without a tool Visual Examinations (Non-Destructive):
and forms a good reseal for storage. As with metal cans, requirements for visual
Structurally, the lug cap consists of a steel examination of closures for glass containers
shell and can have four, six, or eight metal lugs include regular observations for gross closure
depending on its diameter. Normally it contains a defects of at least one container from each capper
flowed-in plastisol gasket. head by a qualified container closure inspection
During closure application the headspace is person.
swept by steam and lug caps are secured to the Required frequency of the visual
glass finish by turning or twisting the cap onto the examination is as often as necessary to ensure
finish to seat the lugs of the cap under the threads proper closure and should not exceed 30 minutes
on the glass finish. of operational time. Additional visual examination
With this lug type of closure the top of the must be performed immediately following a
glass finish makes contact with the gasket on the container jam, machine adjustments or a
inside of the lid. In most instances the lids are prolonged shut down. An example of a prolonged
heated with steam to soften the compound and shutdown may be when the plant ceases
facilitate sealing. Both the lugs and vacuum hold production at 6:00 PM and restarts production at
the cap in place on the glass finish, but vacuum is 8:00 AM the next day.

10
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

Gross closure defects for glass jars include: not be less than 6% of the container volume at the
Loose or cocked caps: "Cocked cap" is a sealing temperature.
condition of the lug-type cap and is caused by a lug Gasket: After the cap is removed there
failing to seat under the glass thread. It is apparent should be a visible, continuous, and even
during a visual examination as it usually results in impression in the plastisol gasket on the underside
an unlevel or tilted cap. of the lid. The impression is made by tight contact
Cap tilt: On PT and lug caps, the cap with the glass finish.
should be approximately level, not cocked or tilted, Cut-thru: "Cut-thru" is a term used to
and seated well down on the finish. This is judged describe when the top of the glass finish has
in relation to the transfer bead located at the pushed completely through the gasket compound
bottom of the container finish . The distance to the metal coating. A cut-thru can result in a
between the bottom of the closure and the transfer leaking seam and requires immediate corrective
bead should not exceed 3/32" action.
Crushed lug: A crushed lug on a lug-type Removal torque: Removal torque is the
cap may or may not be visible during a visual force required to remove the cap. It is typically
examination as it does not necessarily result in a measured using a torque meter. Removal torque is
tilted cap. It is caused by a lug being forced down considered a valuable quality control check but is
over the glass thread during the closure process. not recommended as a control for cap application.
The lugs appear bent inward. Pull-up (Refer to Attachment 22): Pull-up is
Stripped cap: On a lug-type cap, a stripped a non-destructive test for measuring the position of
cap refers to a lug cap that has been over-applied the closure lug on the threads of the glass finish. It
to the extent that the lugs have been stripped is the distance between the leading edge of the cap
through the glass threads on the finish. On visual lug and the vertical neck ring seam on the glass
examination the lugs appear scrapped or finish in 1/16 inch increments. When measuring
scratched. this position, first find the vertical neck ring seam
Low vacuum by visual examination on the glass finish remembering the vertical neck
ring does not always correlate with the two vertical
Physical Examination (Destructive): seams on the glass finish. Then measure the
The regulation requires that physical or distance from the vertical neck ring seam to the
destructive testing be performed by a trained leading edge of the nearest cap lug. A lug
closure technician at intervals of sufficient positioned to the right of the vertical line is referred
frequency to ensure proper closure. Sufficient to as positive (+) and to the left of the vertical line
frequency is defined as intervals not to exceed 4 as negative (-). A positive measurement means the
hours of continuous closing machine operation. 21 cap has been properly applied. A negative lug
CFR Part 113.60(a)(2) also requires that for glass position can indicate an over-application of the cap
containers with vacuum closures, capper efficiency and may result in a stripped cap. Generally, a cap
be checked by measurement of the cold water lug will be about 1/4 inch to the right of the vertical
vacuum (See Vacuum Formation section). The line, however, the distance can vary and
regulation requires that the cold water vacuum measurements between 0" to 8/16" can still result
check be performed before actual filling operations, in a good security value. It is not recommended
and the results recorded. that pull-up measurements replace the "security"
Physical examinations can include: measurements described below, but are useful
Vacuum: Generally there will be vacuum in once the relationship between pull-up and security
the package when it comes out of the capper and has been established.
the panel of the cap will be concave. For a PT cap, Security (Refer to Attachment 22): Security
there must be at least 3" vacuum after capping to values (lug tension of an applied closure) are the
avoid loose caps. Determining vacuum is a most reliable measurement of proper lug cap
destructive test and a standard vacuum gauge is application. Security value ranges are supplied by
used. the closure manufacturer to the processor.
Temperature: The temperature of the Generally, if measured values are always higher
product should be within the normal range for the that the range specified, it indicates a secure
product being run or as specified by the process package with some degree of over-application. If
authority. The product temperature should be measured values are always lower than the range
recorded in conjunction with the vacuum. specified usually indicate under-application. Some
Headspace: Generally, headspace should factors that may affect the measured values are,

11
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

type of plate, compound, and glass surface Refer to Attachment 23 which is an

treatment applied by the container manufacturer. example of glass examination records.
Security measurement is a destructive test.
There is no requirement as to the number of Other Quality Control Equipment:
containers that should be tested; however, being a Other equipment including mechanical
destructive test there are practical limits to the headspacers (which control headspace limits in the
number of containers that one would test. A container) cocked-cap detectors and ejectors, and
security test is performed as follows: dud detectors (which detect low vacuums) are
-Mark a vertical line on the cap and a commonly found on glass-container closing lines
corresponding line on the container. and can affect sealing of the container. For
-Turn cap counter-clockwise until the example, if a headspacer is incorporated in the
vacuum is broken. processing line, it is imperative that it is set
-Reapply the cap until the closure is finger- properly. A headspacer can contribute to product
tight. overhanging the finish by dripping liquid and
-Measure the distance between the marked product on the glass finish, which may affect good
vertical lines in 1/16 inch increments. sealing. Cocked-cap detectors/ejectors and dud
Security is considered positive if the line on detectors, if used, maintained, and set properly,
the cap is to the right of the line on the container can serve as useful tools in the evaluation of
and negative if the line on the cap is to the left of defective seals and sealing problems.
the line on the container. A high positive security
can indicate under application; a negative security
value can indicate over application. The cause of
Retortable Pouch
negative security should be determined and
corrective action taken immediately. Container Structure and Sealing Method:
Security can be measured at the capper Preformed pouches are received by the
and after processing and cooling. The range of food processor from the pouch manufacturerer,
measurement, however, should be lower after who has sealed 3 sides under ideal conditions at
processing due to compound sink that occurs with the pouch manufacturing plant. The pouches are
heat and high pressure. filled by hand, in a straight line fashion or on a
rotary carousel. After filling the packer's end seam
Visual and Physical Examination Record is fusion sealed by the food manufacturer. Prior to
Requirements: sealing, the two sides of the pouch are pulled taut
21 CFR Part 113.60(a) requires that by mechanical grippers to assure that the two
observations made during visual seam sealing surfaces are smooth and parallel to avoid
examinations be recorded. Any defects found wrinkle in the seal area. It is very important to
during the examinations shall also be recorded as prevent food, grease, moisture and other
well as steps taken for corrective action. containants from becoming entrapped in the seal
21 CFR Part 113.100(c) outlines the minimum area; such contaminants can prevent or weaken a
required information for the visual and physical fusion seal.
examination record by stating "Written records of Two common types of heat sealers are hot
all container closure examination shall specify the bar (also called bar or conductance) and impulse
product code, the date and time of container sealers:
closure inspection, the measurements obtained, 1. Hot bar: (jaw type sealing with one or two
and all corrective actions taken." The regulation heated opposed bars) is the most widely used
requires that the records be signed or initialed by method for heat sealing. Each heated bar contains
the container closure inspector and reviewed by a heater element that heats up and remains hot
management with sufficient frequency to ensure during production. A thermocouple is implanted in
that the containers are hermetically sealed. each bar near the surface which is connected by
Sufficient frequency can be defined as prior wire to the instrument control panel where the
to shipment of the product. However, FDA temperature near the sealing surface is digitally
investigators should encourage LACF processors to displayed. The steel bars are usually covered with
review the container records at the same time as teflon to prevent plastic contamination of the bars.
the thermal processing records or not later than Often there is a second cold bar station where the
one working day after the actual process, and prior sealed pouch is pressurized by a set of cold bars to
to shipment or release of the product. set the seal.

12
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

2. Impulse bar: Heating and cooling dwell times testing a number of filled and sealed pouches using
are achieved with one set of sealing bars at one different heat sealing parameters and choosing the
station. Impulse sealers have 2 bars covered with a most ideal parameters (seal bar temperature,
resilient surface such as silicone rubber. A taut pressure and dwell time) for production runs.
Nichrome ribbon (wire) covered with an electrically
insulating layer of thin heat resistant material ,such
as Teflon coated fiberglass, is laid over one or both SEMI-RIGID RETORTABLE TRAYS
of the resilient bars. The bars press the two sealing AND BOWLS:
surfaces through the Nichrome ribbon for a few
seconds which heats the wire to the desired Sealing Method:
temperature for heat sealing. After the specified
Semi-rigid trays and bowls are filled and
heating dwell time, the voltage (heat) is turned off
sealed in a manner similar to the form/filled/sealed
and the resilient bars and pouch seal cools (cooling
web system previously described under pouches.
dwell time). The bars are then opened and the
The trays are filled and vacuum heat sealed using
sealed pouch removed.
hot seal bars. Some of these fill/seal machines
Retort pouches can also be produced on
include a nitrogen gas flush just before fusion heat
site. This is typically called a "form/fill/seal"
sealing a plastic or plastic/foil closure onto the
operation, where a multi-layered laminated web of
container body.
polyester/polypropylene/aluminum foil is run along
a horizontal plane and molded into concave (bowl)
shapes. The pouches are then filled and a
Critical Factors in Sealing:
Critical factors in attaining a good heat seal
continuous web of multi-layer plastic is fed from an
with semi-rigid trays are similar as those for retort
overhead roller on top of the filled pouches. The
pouches. They are:
top web is then heat sealed onto the pouches by
1. Seal bar temperature
heat sealing bars that descend from above. A
2. Seal bar pressure
vacuum is pulled on each pouch just prior to
3. Seal bar dwell time
sealing the two material webs. After sealing, the
4. Smooth, continuous, non-contaminated sealing
individual pouches are cut from the web by a cutter
material surfaces
wheel as the web exits the vacuum heat sealer.

Critical Factors in Sealing: CONTAINER DEFECTS - POUCHES AND

Critical factors in heat sealing the retort SEMI-RIGID RETORTABLE TRAYS /
pouch include: BOWLS AND PAPERBOARD HEAT SEALED
1. Seal bar temperature PACKAGES:
2. Pressure exerted on the seal by the sealing bars National Food Processors Association
3. Dwell time (time seal bar pressure is exerted on (NFPA) has developed a Flexible Package Integrity
seal) Bulletin (BUL 41-L) that defines three classes of
defects for flexible packages. These are:
These critical factors are interdependent.
For example, increased production line speeds and Class I Defects:
shorter dwell time can be compensated for by Class I defects are defined as critical. They
increased seal bar temperature. are gross closure or package defects that result in a
It is also very important to ensure that the hole or leak through the package including a leaky
seal area is not contaminated with food, grease, seal. Some of the more common Class I defects for
moisture or some other contaminant which may pouches and semi-rigid containers are:
contribute to a weak or defective seal. The sealing Channel leaker: A patch or pathway of non-
surface should be smooth, parallel, wrinkle and bonding across the width of the seal, creating a
contaminant free. leak.
During inspections, investigators should Cut: A mechanical slash or slicing that goes
determine if the food processor has validated the into the package with a loss of hermetic seal.
heat sealing equipment being used to assure that Fracture: A break through the packaging
the seal bar temperature, pressure and dwell time material.
parameters are adequate to create a well fused Leaker: A container that is unsealed or
seal. Validation can be accomplished by burst exhibiting evidence of lost integrity.

13
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

Non-bonding: Failure of two sealant films from specification around the periphery of
to combine during the sealing process. container.
Notch leaker: A leak at a manufactured
notch used for easy opening. Class II defects for paperboard heat sealed
Puncture: A mechanical piercing that goes packages are as defined above: abrasion; crushed;
into the package with a loss of hermetic integrity. and misaligned seal.
Swollen package: A package the shape of
which has been altered due to gas formation within Class III Defects:
the package. A Class III defect is defined as a defect that
has no adverse effect on the hermetic seal.
Class I defects for paperboard heat sealed NFPA in cooperation with FDA and the
packages are similar to those for pouches and Association of Official Analytical Chemists
semi-rigid containers and include channel leaker, published a pictorial brochure titled "Classification
cut, puncture, and swollen packages. Additional of Visible Exterior Flexible Package Defects. The
Class I defects for paperboard heat sealed packages brochure along with NFPA BUL 41-L provide
are: valuable information concerning flexible package
Corner leaker: A leak occurring in one of defects. The FDA investigator should be familiar
the corners of the package. with the information contained in these
Perforation leaker: Leakage through or documents.
around a perforated area.
Pull tab leaker: Leakage through or around Seam Evaluation Requirements:
pull tab. 21 CFR Part 113.60(a)(3) specifies that for
Seal leaker: Product leaking along the seal. closures other than double seamed and glass
containers, appropriate detailed inspections and
Class II Defects: tests shall be conducted by qualified personnel at
Class II defects are defined as major. These intervals of sufficient frequency to ensure proper
defects show no sign of visible leakage but are of closing machine performance and consistently
such magnitude that the container may have lost reliable hermetic seal production. The regulation
its hermetic seal. Class II defects for pouches and also states that records of such tests shall be
semi-rigid containers are: recorded.
Abrasion: A scratch partially through the Part 113 does not specify what tests are
surface layer(s) of the package caused by required. The following guidelines are used by the
mechanically rubbing or scuffing. LACF industry for performing both visual and
Blister: A void within the bonded seal destructive tests for flexible and semi-rigid
caused by entrapped grease or moisture vaporizing containers.
during seal formation and then condensing. 1. FDA Bacteriological Analytical Manual (BAM),
Compressed seal: A seal formed by 7th Edition/1992.
excessive pressure and/or heat and evidenced by
cracking and delamination. 2. NFPA Flexible Package Integrity Bulletin, BUL 41-
Contaminated seal: Foreign matter in the L with an accompanying Flexible package Defect
seal areas, such as water, grease, or food. Pictorial Guide, 1989. (As previously mentioned.)
Delamination: A separation of the laminate
materials forming the package. 3. Military Specification "Packaging and Thermal
Misaligned seal: Improper seal position. Pocessing of Foods in Flexible Pouches".
Seal creep:. Partial opening of the inner
border of seal compromising seal width. 4. USDA Regulations 9, CFR Parts 431 "Canning of
Wrinkle: A fold of material in the seal area. Meat and Poultry Products".
Crushed package: Alteration of the
packages' original dimensions caused by force. 5. 1982 USDA bulletins "Test Cycles for Small Size
Uneven impression: Impression from seal Semirigid Containers", "Test Cycles for Small Size
bar is uneven around the periphery of container. Flexible Retortable Pouches" and "Test Cycles for
This could be due to uneven thickness of container Large Size Flexible and Semirigid Containers".
flange resulting in uneven pressure during heat
sealing. Visual Seam Examination (Non-Destructive Test):
Seal width variation: Seal width varies

14
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

As with metal cans and glass jars, 21 CFR regulation does not specify test methods or
Part 113.60(a) requires that regular observations frequency of testing. Again, we rely on the
shall be made during production runs for gross guidelines, previously referenced, that have been
closure defects. The top seal of 1 container from published for these containers. Some of the
each seaming head or lane (for pouches) shall be common destructive and non-destructive testing
visually examined at intervals of sufficient methods for flexible and semi-rigid containers that
frequency and the results recorded. The frequency are described in the guidelines are as follows:
of the visual examination should not exceed 30
minutes of operational time and additional visual Destructive testing:
examination must be performed immediately
following a jam in the closing machine, after Burst testing (Refer to Attachment 24): The
closing machine adjustment, or after startup of a burst test is a good overall test for seal integrity
machine following a prolonged shut down. A (especially for retortable containers). The test
prolonged shut down can be when the plant ceases stresses a package uniformly in all directions and
production at 6:00pm and restarts production at identifies the location of the weakest point and the
8:00 am the next day. pressure at which it fails. The burst test can be
Visual and destructive testing methods and used for retort pouches to test the seal strength
frequencies for flexible and semi-rigid containers along the two sides and one end as well as all four
are outlined in the guidelines referenced above. sides.
For example, NFPA BUL 41-L recommends the Vacuum or bubble test (Refer to
following examinations: Attachment 24): The vacuum or bubble test (also
Retort pouch: Visual on-line examination of referred to as air pressure testing), is performed
the retort pouch container and seals at a rate of 1 inside a transparent vacuum chamber such as a
pouch from each filling station at start-up and bell jar connected to a vacuum source. A vacuum
every 30 minutes thereafter. The visual is pulled on the inside of the chamber for a period
examination includes a "squeeze test" whereby 1 of time and a container or seal leak is indicated if
pouch is manually kneaded 10 times in succession. the container fails to swell to normal dimensions.
After kneading, the seal areas are examined for This can also be done with the container
evidence of product leakage or delamination. submerged under water in the bell jar (bubbles
Plastic containers with heat sealed lids: emanating from the container would indicate a
BUL 41-L recommends a visual examination for leak). This test is most commonly used for
defects every 15 minutes; and at intervals of 30 aseptically filled containers with fusion or peelable
minutes recommends the sides of each plastic test lidstock.
container be manually squeezed to cause the lid to Tensile (seal strength) testing (Refer to
bulge 1/8 inch. The seal area is then visually Attachment 24): The tensile test is used to measure
examined for defects such as contamination and seal strength of the retort pouch. The test involves
non-bonding. taking 3 strips (1"x3") from the seal area of the
Paperboard cartons: BUL 41-L recommends pouch and attaching the two ends of each strip to a
that for web fed systems, the material web be tensile testing device. The device slowly pulls
checked at 15 to 30 minute intervals for correct apart the seam and the force required to separate
alignment of the longitudinal seal. After sealing the seam is measured. The disadvantage of tensile
the cartons should be checked for proper testing is it tests only sampled portions of the seam
alignment of transverse seals and for evidence of area. For this reason, it is used only for
container defects. surveillance of material sealability and to spot
check equipment operations and sealing
Physical examination (destructive and non- conditions.
destructive testing): Drop testing (Refer to Attachment 25): The
As stated previously, 21 CFR Part drop test (also referred to as an immediate
113.60(a)(2) states that for closures other than container abuse test) is commonly used to test the
double seams and glass containers, appropriate package and seal integrity of flexible containers,
detailed inspections and tests shall be conducted at and semirigid trays and bowls. This test was
intervals of sufficient frequency to ensure proper designed to simulate the dropping of individual
closing machine performance and consistently containers under a controlled and reproducible
reliable hermetic seal production. For physical basis. After drop testing, each container is visually
testing of the reliability of the hermetic seal the inspected for evidence of leakage. After the visual

15
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

inspection, the container is then "peel tested". Peel processing and/or storage. Biotesting involves
testing is described below. filling containers with a broth or other food
Peel testing (Refer to Attachment 26): The conducive to growth of gas producing
peel test is intended to measure the pounds of microorganisms and then subjecting the container
force necessary to peel a fused or sealed lid off a to processing or abuse, followed by immersion in
plastic container body. For the form/filled/sealed a solution heavily contaminated with the target
plastic containers, the peel test is conducted by spoilage organism. The containers are then
peeling back the lid on each container held at a 45 incubated. After incubation, a leak would be
degree angle and observing the area for a general evidenced by a swollen container.
frosty appearance on both the lid and sealed On-Line non-destructive tests: There are a
surfaces. This frosty material is polypropylene number of on-line non-destructive tests designed
residue from the lid sealing layer. The presence of to detect leaks in semi-rigid and flexible packages
this material on the flange, around the periphery of after filling and sealing. Most of these tests involve
the container, indicates a well fused seam. Peel the measurement of pressure differential between
testing can be performed by hand or with the use the pressure inside the container and the external
of a tensile testing device. This test is often pressure. After establishing a set differential
performed after drop testing as previously pressure, any change in pressure would indicate a
described. leak.
Residual Gas testing (Refer to Attachment These test methods although not required
27): The quantity of residual gas in retortable by regulation, are presented in detail in various
flexible pouches and semirigid plastic containers is guidelines, as previously referenced.
normally measured prior to retorting. Too much
residual air can exert excessive pressure on the Visual and Physical Seam Examination Record
inner seal area during retorting, which results in Requirements:
weakened seals and reduced heat penetration to The regulation requires that observations
the product cold spot. To much air in the product made during visual and physical examinations be
can also shorted the product shelf life. recorded. Any defects found during the visual
Electroconductivity testing (Refer to examination shall also be recorded, as well as
Attachment 27): Electroconductivity testing tests a steps taken for corrective action.
container's ability to prevent the flow of electric Although the regulation does not specify
current through the package. A tight inner layer of what test methods or frequency of examination is
plastic material will not allow the flow through of required, it does say that tests will be performed
electric current unless there is a hole or crack in the and "Records of such tests shall be maintained. 21
plastic material. Electroconductivity tests are CFR Part 113.100(c) requires the written container
commonly run to confirm leaks in packages closure records must specify the product code, date
detected by other non-destructive tests such as and time of container closure inspection, any
incubation. measurements obtained, and all corrective actions
Dye testing: Dye tests are usually taken. These records must also be signed or
conducted to identify the location of micro size initialed by the container closure inspector and
holes in food packages that have tested positive for reviewed by management with sufficient frequency
leaks by electroconductivity, incubation or biotest to ensure adequate hermetic seal production.
methods.

Non-destructive testing: REFERENCES

Incubation testing : Incubation testing "Canned Foods, Principles of Thermal Process
involves the storage of finished product samples Control, Acidification and Container Closure
for a week or more at temperatures within the Evaluation", 1988 and 1995, The Food Processors
range required for growth of spoilage Institute, Washington, DC.
microorganisms. The growth of microorganisms
indicates either insufficient processing or a loss of Flexible Packaging Used in the Thermal Processing
hermetic seal. and Aseptic Filling of Low Acid Foods, Brian
Biotesting: Biotesting is a means of Hendrickson, 1989.
challenging a containers's ability to prevent
leakage under the worst case conditions of Food and Drug Administration State Training

16
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

Branch Course Manuals, "Low Acid Canned Foods",

U. S. Department of Health and Human Services,
Food and Drug Administration, 1996.

Food Packaging Principles and Practice, Gordon L.

Robertson, Marcel Dekker, Inc., New York 1993

NFPA Bulletin 41-L, "Flexible Package Integrity

Bulletin" The Flexible Package Integrity Committee,
National Food Processor's Association, 1989,
Washington, D.C.

Pictorial Poster "Classification of Visible Exterior

Can Defects", Published by AOAC, 1984

Pictorial poster of flexible package defects, The

NFPA Flexible Package Integrity Committee, 1989

Report by Meal Ready-To Eat (MRE) Task Force,

Office of the Deputy Chief of Staff for Logistics
Headquarters, Dept. of the Army, The Pentagon,
Washington, D.C., July 1986.

Test Cycles for Large Size Flexible and Semi-rigid

Containers, USDA, Washington, D.C., 1982.

Test Cycles for Small Size Flexible Retortable

Pouches, USDA, Washington, D.C., 1982.

Test Cycles for Small Size Semi-rigid Containers,

USDA, Washington, D.C., 1982.

The FDA Bacteriological Analytical Manual (BAM),

7th Edition, 1992, Published by AOAC International.

The Wiley Encyclopedia of Packaging Technology,

Second Edition, Aron L. Brody and Kenneth S.
Marsh; John Wiley & Sons, Inc., New York, 1997.

Title 21 Code of Federal Regulations Part 113-

Thermally Processed Low-Acid Foods Packaged in
Hermetically Sealed Containers.

Title 9 Code of Federal Regulations Part 431-

Canning of Meat and Poultry Products.

"Top Double Seaming Manual", Department of

Food Science and Technology of Oregon State
University, 1977.

U.S. Military Specification, MIL-PRF47073E,

Packaging and Thermal Processing of Foods in
Flexible Pouches, 30 November, 1995.

17
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

ATTACHMENTS:
1. Metal Can Flange/ Metal Can End Curl/ Double Seam Structure and Terminology
2. Double Seam - Countersink/Thickness/ Width/Body Hook and Cover Hook/Overlap/Cover Hook Wrinkles
3. Seam Tightness Evaluation
4. Body Wall Impression
5. Formation of the Double Seam
6. Stages in the Formation of the Double Seam-1st and 2nd Operation Roll
7. Example- Double Seam Guidelines
8. Can Seam Defects - Droop, Lips, Vees
9. Can Seam Defects - Sharp Seams, Cut-Overs
10.Can Seam Defect - Jumpover
11. Can Seam Defects - Deadheads, Spinner, Slips and Skids
12. Can Seam Defects - False Seam/ Knocked Down Flange/Body Buckle/Cocked Body
13. Can Seam Defect - Cut Seam
14. Can Seam Projector
15. Can Seam Micrometer
16. Seamscope
17. Example-Visual Seam Examination Record-Cans
18. Double Seam Examination Records - Cans
19. Glass Container Structure and Terminology/ Metal Vacuum Closure Structure and Terminology
20. Metal Vacuum Closures
21. Glass Container Defects
22. Security Test/Pull-Up Test
23. Example-Glass Closure Evaluation Records
24. Sealed Pouches and Semi-Rigid Containers-Burst Test/Bubble Test
25. Sealed Pouches and Semi-Rigid Containers-USDA Drop Test
26. Sealed Pouches and Semi-Rigid Containers-Peel Test
27. Sealed Pouches and Semi-Rigid Containers- Residual Gas Test/Electroconductivity Test

18
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

19
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

20
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

21
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

22
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

23
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

24
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

25
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

26
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

27
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

28
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

29
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

30
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

31
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

32
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

33
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

34
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

35
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

36
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

37
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

38
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

39
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

40
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

41
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

42
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

43
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

44
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

45
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

46
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

47
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

48
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

49
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

50
FDA/CFSAN BAM - Examination of Canned Foods Page 1 of 22

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 21A
Examination of Canned Foods
Authors

(Return to Table of Contents)

The incidence of spoilage in canned foods is low, but when it occurs it must be investigated properly.
Swollen cans often indicate a spoiled product. During spoilage, cans may progress from normal to
flipper, to springer, to soft swell, to hard swell. However, spoilage is not the only cause of abnormal
cans. Overfilling, buckling, denting, or closing while cool may also be responsible. Microbial spoilage
and hydrogen, produced by the interaction of acids in the food product with the metals of the can, are the
principal causes of swelling. High summer temperatures and high altitudes may also increase the degree
of swelling. Some microorganisms that grow in canned foods, however, do not produce gas and
therefore cause no abnormal appearance of the can; nevertheless, they cause spoilage of the product.

Spoilage is usually caused by growth of microorganisms following leakage or underprocessing. Leakage

occurs from can defects, punctures, or rough handling. Contaminated cooling water sometimes leaks to
the interior through pinholes or poor seams and introduces bacteria that cause spoilage. A viable mixed
microflora of bacterial rods and cocci is indicative of leakage, which may usually be confirmed by can
examination. Underprocessing may be caused by undercooking; retort operations that are faulty because
of inaccurate or improperly functioning thermometers, gauges, or controls; excessive contamination of
the product for which normally adequate processes are insufficient; changes in formulation or handling
of the product that result in a more viscous product or tighter packing in the container, with consequent
lengthening of the heat penetration time; or, sometimes, accidental bypassing of the retort operation
altogether. When the can contains a spoiled product and no viable microorganisms, spoilage may have
occurred before processing or the microorganisms causing the spoilage may have died during storage.

Underprocessed and leaking cans are of major concern and both pose potential health hazards. However,
before a decision can be made regarding the potential health hazard of a low-acid canned food, certain
basic information is necessary. Naturally, if Clostridium botulinum (spores, toxin, or both) is found, the
hazard is obvious. Intact cans that contain only mesophilic, Gram-positive, sporeforming rods should be
considered underprocessed, unless proved otherwise. It must be determined that the can is intact
(commercially acceptable seams and no microleaks) and that other factors that may lead to
underprocessing, such as drained weight and product formulation, have been evaluated.

The preferred type of tool for can content examination is a bacteriological can opener consisting of a

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 2 of 22

puncturing device at the end of a metal rod mounted with a sliding triangular blade that is held in place
by a set screw. The advantage over other types of openers is that it does no damage to the double seam
and therefore will not interfere with subsequent seam examination of the can.

Table 1. Useful descriptive terms for canned food analysis.

Exterior can condition Internal can condition

leaker normal
dented peeling
rusted slight, moderate or severe etching
buckled slight, moderate or severe
paneled blackening
bulge slight, moderate or severe rusting
mechanical damage
Micro-leak test Product odor Product liquor
packer seam putrid cloudy
side panel acidic clear
side seam butyric foreign
cut code metallic frothy
pinhole sour
cheesy
fermented
musty
sweet
fecal
sulfur
off-odor
Solid product Liquid product Pigment Consistency
digested cloudy darkened slimy
softened clear light fluid
curdled foreign changed viscous
uncooked frothy ropy
overcooked

Flat - a can with both ends concave; it remains in this condition even when the can
is brought down sharply on its end on a solid, flat surface.
Flipper - a can that normally appears flat; when brought down sharply on its end
on a flat surface, one end flips out. When pressure is applied to this end, it flips in
again and the can appears flat.
Springer - a can with one end permanently bulged. When sufficient pressure is
applied to this end, it will flip in, but the other end will flip out.
Soft swell - a can bulged at both ends, but not so tightly that the ends cannot be
pushed in somewhat with thumb pressure.
Hard swell - a can bulged at both ends, and so tightly that no indentation can be
made with thumb pressure. A hard swell will generally "buckle" before the can
bursts. Bursting usually occurs at the double seam over the side seam lap, or in the
middle of the side seam.

The number of cans examined bacteriologically should be large enough to give reliable results. When
the cause of spoilage is clear-cut, culturing 4-6 cans may be adequate, but in some cases it may be

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 3 of 22

necessary to culture 10-50 cans before the cause of spoilage can be determined. On special occasions
these procedures may not yield all the required information, and additional tests must be devised to
collect the necessary data. Unspoiled cans may be examined bacteriologically to determine the presence
of viable but dormant organisms. The procedure is the same as that used for spoiled foods except that
the number of cans examined and the quantity of material subcultured must be increased.

A. Equipment and materials

1. Incubators, thermostatically controlled at 30, 35, and 55°C

2. pH meter, potentiometer
3. Microscope, slides, and coverslips
4. Can opener, bacteriological can opener, and can punch, all sterile
5. Petri dishes, sterile
6. Test tubes, sterile
7. Serological pipets, cotton-plugged, sterile
8. Nontapered pipets, cotton-plugged (8 mm tubing), sterile
9. Soap, water, brush, and towels, sterile and nonsterile
10. Indelible ink marking pen
11. Diamond point pen for marking cans
12. Examination pans (Pyrex or enamel baking pans)

B. Media and reagents

1. Bromcresol purple (BCP) dextrose broth (M27)

2. Chopped liver broth (M38) or cooked meat medium (CMM) (M42)
3. Malt extract broth (M94)
4. Liver-veal agar (without egg yolk) (LVA) (M83)
5. Acid broth (M4)
6. Nutrient agar (NA) (M112)
7. Methylene blue stain (R45), crystal violet (R16), or Gram stain (R32)
8. Sabouraud's dextrose agar (SAB) (M133)
9. 4% Iodine in 70% ethanol (R18)

C. Can preparation

Remove labels. With marking pen, transfer subnumbers to side of can to aid in correlating
findings with code. Mark labels so that they may be replaced in their original position on the can
to help locate defects indicated by stains on label. Separate all cans by code numbers and record
size of container, code, product, condition, evidence of leakage, pinholes or rusting, dents,
buckling or other abnormality, and all identifying marks on label. Classify each can according to
the descriptive terms in Table 1. Before observing cans for classification, make sure cans are at
room temperature.

D. Examination of can and contents

Classification of cans. NOTE: Cans must be at room temperature for classification.

1. Sampling can contents

a. Swollen cans. Immediately analyze springers, swells, and a representative number (at

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 4 of 22

least 6, if available) of flat and flipper cans. Retain examples of each, if available,
when reserve portion must be held. Place remaining flat and flipper cans (excluding
those held in reserve) in incubator at 35°C. Examine at frequent intervals for 14 days.
When abnormal can or one becoming increasingly swollen is found, make note of it.
When can becomes a hard swell or when swelling no longer progresses, culture
sampled contents, examine for preformed toxin of C. botulinum if microscopic
examination shows typical C. botulinum organisms or Gram-positive rods, and
perform remaining steps of canned food examination.

b. Flat and flipper cans. Place cans (excluding those held in reserve) in incubator at
35°C. Observe cans for progressive swelling at frequent intervals for 14 days. When
swelling occurs, follow directions in l-a, above. After 14 days remove flat and flipper
cans from incubator and test at least 6, if available. (It is not necessary to analyze all
normal cans.) Do not incubate cans at temperatures above 35°C. After incubation,
bring cans back to room temperature before classifying them.

2. Opening the can. Open can in an environment that is as aseptic as possible. Use of vertical
laminar flow hood is recommended.

a. Hard swells, soft swells, and springers. Chill hard swells in refrigerator before
opening. Scrub entire uncoded end and adjacent sides of can using abrasive cleanser,
cold water, and a brush, steel wool, or abrasive pad. Rinse and dry with clean sterile
towel. Sanitize can end to be opened with 4% iodine in 70% ethanol for 30 min and
wipe off with sterile towel. DO NOT FLAME. Badly swollen cans may spray out a
portion of the contents, which may be toxic. Take some precaution to guard against
this hazard, e.g., cover can with sterile towel or invert sterile funnel over can.
Sterilize can opener by flaming until it is almost red, or use separate presterilized can
openers, one for each can. At the time a swollen can is punctured, test for headspace
gas, using a qualitative test or the gas-liquid chromatography method described
below. For a qualitative test, hold mouth of sterile test tube at puncture site to capture
some escaping gas, or use can-puncturing press to capture some escaping gas in a
syringe. Flip mouth of tube to flame of Bunsen burner. A slight explosion indicates
presence of hydrogen. Immediately turn tube upright and pour in a small amount of
lime water. A white precipitate indicates presence of CO2. Make opening in sterilized
end of can large enough to permit removal of sample.

b. Flipper and flat cans. Scrub entire uncoded end and adjacent sides of can using
abrasive cleanser, warm water, and a brush, steel wool, or abrasive pad. Rinse and dry
with clean sterile towel. Gently shake cans to mix contents before sanitizing. Flood
end of can with iodine-ethanol solution and let stand at least 15 min. Wipe off iodine
mixture with clean sterile towel. Ensure sterility of can end by flaming with burner in
a hood until iodine-ethanol solution is burned off, end of can becomes discolored
from flame, and heat causes metal to expand. Be careful not to inhale iodine fumes
while burning off can end. Sterilize can opener by flaming until it is almost red, or
use separate presterilized can openers for each can. Make opening in sterilized end of
can large enough to permit removal of sample.

3. Removal of material for testing. Remove large enough portions from center of can to
inoculate required culture media. Use sterile pipets, either regular or wide-mouthed.
Transfer solid pieces with sterile spatulas or other sterile devices. Always use safety devices

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 5 of 22

for pipetting. After removal of inocula, aseptically transfer at least 30 ml or, if less is
available, all remaining contents of cans to sterile closed containers, and refrigerate at about
4°C. Use this material for repeat examination if needed and for possible toxicity tests. This
is the reserve sample. Unless circumstances dictate otherwise, analyze normal cans
submitted with sample organoleptically and physically (see 5-b, below), including pH
determination and seam teardown and evaluation. Simply and completely describe product
appearance, consistency, and odor on worksheet. If analyst is not familiar with
decomposition odors of canned food, another analyst, preferably one familiar with
decomposition odors, should confirm this organoleptic evaluation. In describing the product
in the can, include such things as low liquid level (state how low), evidence of compaction,
if apparent, and any other characteristics that do not appear normal. Describe internal and
external condition of can, including evidence of leakage, etching, corrosion, etc.

4. Physical examination. Perform net weight determinations on a representative number of

cans examined (normal and abnormal). Determine drained weight, vacuum, and headspace
on a representative number of normal-appearing and abnormal cans (1). Examine metal
container integrity of a representative number of normal cans and all abnormal cans that are
not too badly buckled for this purpose (see Chapter 22). CAUTION: Always use care when
handling the product, even apparently normal cans, because botulinal toxin may be present.

5. Cultural examination of low-acid food (pH greater than 4.6). If there is any question as
to product pH range, determine pH of a representative number of normal cans before
proceeding. From each container, inoculate 4 tubes of chopped liver broth or cooked meat
medium previously heated to 100°C (boiling) and rapidly cooled to room temperature; also
inoculate 4 tubes of bromcresol purple dextrose broth. Inoculate each tube with 1-2 ml of
product liquid or product-water mixture, or 1-2 g of solid material. Incubate as in Table 2.

Table 2. Incubation times for various media for examination of low acid foods (pH > 4.6).

Medium No. of tubes Temp. (°C) Time of incubation (h)

Chopped liver (cooked meat) 2 35 96-120
Chopped liver (cooked meat) 2 55 24-72
Bromcresol purple dextrose broth 2 55 24-48
Bromcresol purple dextrose broth 2 35 96-120

After culturing and removing reserve sample, test material from cans (other than those
classified as flat) for preformed toxins of C. botulinum when appropriate, as described in
Chapter 17.

a. Microscopic examination. Prepare direct smears from contents of each can after
culturing. Dry, fix, and stain with methylene blue, crystal violet, or Gram stain. If
product is oily, add xylene to a warm, fixed film, using a dropper; rinse and stain. If
product washes off slide during preparation, examine contents as wet mount or
hanging drop, or prepare suspension of test material in drop of chopped liver broth
before drying. Check liver broth before use to be sure no bacteria are present to
contribute to the smear. Examine under microscope; record types of bacteria seen and
estimate total number per field.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 6 of 22

b. Physical and organoleptic examination of can contents. After removing reserve

sample from can, determine pH of remainder, using pH meter. DO NOT USE pH
PAPER. Pour contents of cans into examination pans. Examine for odor, color,
consistency, texture, and overall quality. DO NOT TASTE THE PRODUCT.
Examine can lining for blackening, detinning, and pitting.

Table 3.Schematic diagram of culture procedure for low-acid canned foods

aLVA, liver-veal agar; NA, nutrient agar; CMM, cooked meat medium; BCP, bromcresol purple
dextrose broth.

Table 4. Incubation of acid broth and malt extract broth used for acid foods (pH 4.6)

Medium No. of tubes Temp. (°C) Time of incubation (h)

Acid broth 2 55 48
Acid broth 2 30 96
Malt extract broth 2 30 96

Table 5. Pure culture scheme for acid foods (pH 4.6).

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 7 of 22

a NA, nutrient agar; SAB, Sabouraud's dextrose agar.

E. Cultural findings in cooked meat medium (CMM) and bromcresol purple dextrose broth (BCP)

Check incubated medium for growth at frequent intervals up to maximum time of incubation
(Table 2). If there is no growth in either medium, report and discard. At time growth is noted
streak 2 plates of liver-veal agar (without egg yolk) or nutrient agar from each positive tube.
Incubate one plate aerobically and one anaerobically, as in schematic diagram (Table 3).
Reincubate CMM at 35°C for maximum of 5 days for use in future toxin studies. Pick
representatives of all morphologically different types of colonies into CMM and incubate for
appropriate time, i.e., when growth is sufficient for subculture. Dispel oxygen from CMM broths
to be used for anaerobes but not from those to be used for aerobes. After obtaining pure isolates,
store cultures to maintain viability.

1. If mixed microflora is found only in BCP, report morphological types. If rods are
included among mixed microflora in CMM, test CMM for toxin, as described in Chapter
17. If Gram-positive or Gram-variable rods typical of either Bacillus or Clostridium
organisms are found in the absence of other morphological types, search to determine
whether spores are present. In some cases, old vegetative cells may appear to be Gram-
negative and should be treated as if they are Gram-positive. Test culture for toxin according
to Chapter 17.

Table 6. Classification of food products according to acidity

Low acid--pH greater than 4.6 Acid pH 4.6 and below

Meats Tomatoes
Seafoods Pears
Milk Pineapple

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 8 of 22

Meat and vegetable Mixtures and "specialties" Other fruit

Spaghetti
Soups Sauerkraut
Vegetables Pickles
Asparagus
Beets Berries
Pumpkin
Green beans Citrus
Corn
Lima beans Rhubarb

Table 7. Spoilage microorganisms that cause high and low acidity in various
vegetables and fruits

Spoilage type pH groups Examples

Thermophilic
Flat-sour >5.3 Corn, peas
Thermophilic(a) >4.8 Spinach, corn
Sulfide spoilage(a) >5.3 Corn, peas
Mesophilic
Putrefactive anaerobes(a) >4.8 Corn, asparagus
Butyric anaerobes >4.0 Tomatoes, peas
Aciduric flat-sour(a) >4.2 Tomato juice

Lactobacilli 4.5-3.7 Fruits

Yeasts <3.7 Fruits
Molds <3.7 Fruits

a The responsible organisms are bacterial sporeformers.

Table 8. Spoilage manifestations in low-acid products

Group of Classification Manifestations
organisms
Flat-sour Can flat Possible loss of vacuum on storage
Product Appearance not usually altered; pH markedly
lowered, sour; may have slightly abnormal
odor; sometimes cloudy liquor
Thermophilic Can swells May burst
anaerobe Product Fermented, sour, cheesy or butyric odor

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 9 of 22

Sulfide spoilage Can flat H2S gas absorbed by product

Product Usually blackened; rotten egg odor
Putrefactive Can swells May burst
anaerobe Product May be partially digested; pH slightly above
normal; typical putrid odor
Aerobic Can flat or Usually no swelling, except in cured meats
sporeformers swollen when nitrate and sugar present; coagulated
evaporated milk, black beets

Table 9. Spoilage manifestations in acid products

Type of organism Classification Manifestation
Bacillus thermoacidurans (flat, Can flat Little change in vacuum
sour tomato juice) Product Slight pH change; off-odor
Butyric anaerobes (tomatoes and Can swells May burst
tomato juice) Product Fermented, butyric odor
Nonsporeformers (mostly lactic Can swells Usually burst, but swelling
types) may be arrested
Product Acid odor

Table 10. Laboratory diagnosis of bacterial spoilage

Underprocessed Leakage
Can Flat or swelled; seams generally normal Swelled; may show
normal defects(a)
Product Sloppy or fermented Frothy fermentation;
appearance viscous
odor Normal, sour or putrid, but generally Sour, fecal; generally
consistent from can to can varying from can to can
pH Usually fairly constant Wide variation
Microscopic Cultures show sporeforming rods only Mixed cultures,
and cultural generally rods and cocci;
only at usual
temperatures
Growth at 35 and/or 55°C. May be
characteristic on special growth media,
e.g., acid agar for tomato juice.

If product misses retort completely,

rods, cocci,yeast or molds, or any
combination of these may be present.
History Spoilage usually confined to certain Spoilage scattered

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 10 of 22

portions of pack
In acid products, diagnosis may be less
clearly defined; similar organisms may
be involved in understerilization and
leakage.
aLeakage may be due not to can defects but to other factors, such as
contamination of cooling water or rough handling, e.g., can unscramblers, rough
conveyor system.

Table 11. pH range of a few selected commercially canned foods

Food pH range Food pH range

Apples, juice 3.3 - 3.5 Jam, fruit 3.5 - 4.0

Apples, whole 3.4 - 3.5 Jellies, fruit 3.0 - 3.5
Asparagus, green 5.0 - 5.8 Lemon juice 2.2 - 2.6
Beans Lemons 2.2 - 2.4
Baked 4.8 - 5.5 Lime juice 2.2 - 2.4
Green 4.9 - 5.5 Loganberries 2.7 - 3.5
Lima 5.4 - 6.3 Mackerel 5.9 - 6.2
Soy 6.0 - 6.6 Milk
Beans with pork 5.1 - 5.8 Cow, whole 6.4 - 6.8
Beef, corned, hash 5.5 - 6.0 Evaporated 5.9 - 6.3
Beets, whole 4.9 - 5.8 Molasses 5.0 - 5.4
Blackberries 3.0 - 4.2 Mushroom 6.0 - 6.5
Blueberries 3.2 - 3.6 Olives, ripe 5.9 - 7.3
Boysenberries 3.0 - 3.3 Orange juice 3.0 - 4.0
Bread Oysters 6.3 - 6.7
White 5.0 - 6.0 Peaches 3.4 - 4.2
Date and nut 5.1 - 5.6 Pears (Bartlett) 3.8 - 4.6
Broccoli 5.2 - 6.0 Peas 5.6 - 6.5
Carrot juice 5.2 - 5.8 Pickles
Carrots, chopped 5.3 - 5.6 Dill 2.6 - 3.8
Cheese Sour 3.0 - 3.5
Parmesan 5.2 - 5.3 Sweet 2.5 - 3.0
Roquefort 4.7 - 4.8 Pimento 4.3 - 4.9
Cherry juice 3.4 - 3.6 Pineapple
Chicken 6.2 - 6.4 Crushed 3.2 - 4.0
Chicken with noodles 6.2 - 6.7 Juice 3.4 - 3.7

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 11 of 22

Chop suey 5.4 - 5.6 Sliced 3.5 - 4.1

Cider 2.9 - 3.3 Plums 2.8 - 3.0
Clams 5.9 - 7.1 Potato salad 3.9 - 4.6
Cod fish 6.0 - 6.1 Potatoes
Corn Mashed 5.1
Cream style 5.9 - 6.5 White, whole 5.4 - 5.9
On-the-cob 6.1 - 6.8 Prune juice 3.7 - 4.3
Whole grain Pumpkin 5.2 - 5.5
Brine-packed Raspberries 2.9 - 3.7
Vacuum-packed 6.0 - 6.4 Rhubarb 2.9 - 3.3
Crab apples, spiced 3.3 - 3.7 Salmon 6.1 - 6.5
Cranberry Sardines 5.7 - 6.6
Juice 2.5 - 2.7 Sauerkraut 3.1 - 3.7
Sauce 2.3 Juice 3.3 - 3.4
Currant juice 3.0 Shrimp 6.8 - 7.0
Dates 6.2 - 6.4 Soups
Duck 6.0 - 6.1 Bean 5.7 - 5.8
Figs 4.9 - 5.0 Beef broth 6.0 - 6.2
Frankfurters 6.2 - 6.2 Chicken noodle 5.5 - 6.5
Fruit cocktail 3.6 - 4.0 Clam chowder 5.6 - 5.9
Gooseberries 2.8 - 3.1 Duck 5.0 - 5.7
Grapefruit Mushroom 6.3 - 6.7
Juice 2.9 - 3.4 Noodle 5.6 - 5.8
Pulp 3.4 Oyster 6.5 - 6.9
Sections 3.0 - 3.5 Pea 5.7 - 6.2
Grapes 3.5 - 4.5 Spinach 4.8 - 5.8
Ham, spiced 6.0 - 6.3 Squash 5.0 - 5.8
Hominy, lye 6.9 - 7.9 Tomato 4.2 - 5.2
Huckleberries 2.8 - 2.9 Turtle 5.2 - 5.3
Vegetable 4.7 - 5.6
Strawberries 3.0 - 3.9 Miscellaneous products
Sweet potatoes 5.3 - 5.6 Beers 4.0 - 5.0
Tomato juice 3.9 - 4.4 Ginger ale 2.0 - 4.0
Tomatoes 4.1 - 4.4 Human
Tuna 5.9 - 6.1 Blood plasma 7.3 - 7.5
Turnip greens 5.4 - 5.6 Duodenal contents 4.8 - 8.2
Vegetable juice 3.9 - 4.3 Feces 4.6 - 8.4
Vegetables, mixed 5.4 - 5.6 Gastric contents 1.0 - 3.0

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 12 of 22

Vinegar 2.4 - 3.4 Milk 6.6 - 7.6

Youngberries 3.0 - 3.7 Saliva 6.0 - 7.6
Spinal fluid 7.3 - 7.5
Urine 4.8 - 8.4
Magnesia, milk of 10.0 -10.5
Water
Distilled, CO2 6.8 - 7.0
Mineral 6.2 - 9.4
Sea 8.0 - 8.4
Wine 2.3 - 3.8

2. If no toxin is present, send pure cultures for evaluation of heat resistance to Cincinnati
District Office, FDA, 1141 Central Parkway, Cincinnati, OH 45202, if cultures meet the
following criteria:

„ Cultures come from intact cans that are free of leaks and have commercially
acceptable seams. (Can seams of both ends of can must be measured; visual
examination alone is not sufficient.)

„ Two or more tubes are positive and contain similar morphological types.

3. Examination of acid foods (pH 4.6 and below) by cultivation. From each can, inoculate 4
tubes of acid broth and 2 tubes of malt extract broth with 1-2 ml or 1-2 g of product, using
the same procedures as for low-acid foods, and incubate as in Table 4. Record presence or
absence of growth in each tube, and from those that show evidence of growth, make smears
and stain. Report types of organisms seen. Pure cultures may be isolated as shown in Table
5.

F. Interpretation of results (see Tables 6-11)

1. The presence of only sporeforming bacteria, which grow at 35°C, in cans with satisfactory
seams and no microleaks indicates underprocessing if their heat resistance is equal to or less
than that of C. botulinum. Spoilage by thermophilic anaerobes such as C. thermobutylicum
may be indicated by gas in cooked meat at 55°C and a cheesy odor. Spoilage by C.
botulinum, C. sporogenes, or C. perfringens may be indicated in cooked meat at 35°C by
gas and a putrid odor; rods, spores, and clostridial forms may be seen on microscopic
examination. Always test supernatants of such cultures for botulinal toxin even if no toxin
was found in the product itself, since viable botulinal spores in canned foods indicate a
potential public health hazard, requiring recall of all cans bearing the same code. Spoilage
by mesophilic organisms such as Bacillus thermoacidurans or B. coagulans and/or
thermophilic organisms such as B. stearothermophilus, which are flat-sour types, may be
indicated by acid production in BCP tubes at 35 and/or 55°C in high-acid or low-acid
canned foods. No definitive conclusions may be drawn from inspection of cultures in broth
if the food produced an initial turbidity on inoculation. Presence or absence of growth in
this case must be determined by subculturing.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 13 of 22

2. Spoilage in acid products is usually caused by nonsporeforming lactobacilli and yeasts.

Cans of spoiled tomatoes and tomato juice remain flat but the products have an off-odor,
with or without lowered pH, due to aerobic, mesophilic, and thermophilic sporeformers.
Spoilage of this type is an exception to the general rule that products below pH 4.6 are
immune to spoilage by sporeformers. Many canned foods contain thermophiles which do
not grow under normal storage conditions, but which grow and cause spoilage when the
product is subjected to elevated temperatures (50-55°C). B. thermoacidurans and B.
stearothermophilus are thermophiles responsible for flat-sour decomposition in acid and
low-acid foods, respectively. Incubation at 55°C will not cause a change in the appearance
of the can, but the product has an off-odor with or without a lowered pH. Spoilage
encountered in products such as tomatoes, pears, figs, and pineapples is occasionally caused
by C. pasteurianum, a sporeforming anaerobe which produces gas and a butyric acid odor.
C. thermosaccolyticum is a thermophilic anaerobe which causes swelling of the can and a
cheesy odor of the product. Cans which bypass the retort without heat processing usually
are contaminated with nonsporeformers as well as sporeformers, a spoilage characteristic
similar to that resulting from leakage.

3. A mixed microflora of viable bacterial rods and cocci usually indicates leakage. Can
examination may not substantiate the bacteriological findings, but leakage at some time in
the past must be presumed. Alternatively, the cans may have missed the retort altogether, in
which case a high rate of swells would also be expected.

4. A mixed microflora in the product, as shown by direct smear, in which there are large
numbers of bacteria visible but no growth in the cultures, may indicate precanning spoilage.
This results from bacterial growth in the product before canning. The product may be
abnormal in pH, odor, and appearance.

5. If no evidence of microbial growth can be found in swelled cans, the swelling may be due to
development of hydrogen by chemical action of contents on container interiors. The
proportion of hydrogen varies with the length and condition of storage. Thermophilic
anaerobes produce gas, and since cells disintegrate rapidly after growth, it is possible to
confuse thermophilic spoilage with hydrogen swells. Chemical breakdown of the product
may result in evolution of carbon dioxide. This is particularly true of concentrated products
containing sugar and some acid, such as tomato paste, molasses, mincemeats, and highly
sugared fruits. The reaction is accelerated at elevated temperatures.

6. Any organisms isolated from normal cans that have obvious vacuum and normal product
but no organisms in the direct smear should be suspected as being a laboratory contaminant.
To confirm, aseptically inoculate growing organism into another normal can, solder the hole
closed, and incubate 14 days at 35°C. If any swelling of container or product changes occur,
the organism was probably not in the original sample. If can remains flat, open it aseptically
and subculture as previously described. If a culture of the same organism is recovered and
the product is normal, consider the product commercially sterile since the organism does not
grow under normal conditions of storage and distribution.

Headspace Gas Determination by Gas-Liquid Chromatography

Nitrogen, the principal gas normally present in canned foods during storage, is associated with lesser
quantities of carbon dioxide and hydrogen. Oxygen included in the container at the time of closure is
initially dissipated by container corrosion and/or product oxidation. Departure from this normal pattern

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 14 of 22

can serve as an important indication of changes within the container, since the composition of headspace
gases may distinguish whether bacterial spoilage, container corrosion, or product deterioration is the
cause of swollen cans (2). Use of the gas chromatograph for analyzing headspace gases of abnormal
canned foods has eliminated the possibility of false-negative tests for different gases. It has also allowed
the analyst to determine the percentage of each gas present, no matter what the mixture is. By knowing
these percentages, the analyst can be alerted to possible can deterioration problems or bacterial spoilage.
A rapid gas-liquid chromatographic procedure is presented here for the determination of carbon dioxide,
hydrogen, oxygen, nitrogen, and hydrogen sulfide from the headspace of abnormal canned foods.

The analysis of 2352 abnormal canned foods, composed of 288 different products by a gas-liquid
chromatography showed viable microorganisms in 256 cans (3). Analysis of this data showed that
greater than 10 percent carbon dioxide in the headspace gas was indicative of microbial growth.
Although greater than 10 percent carbon dioxide is found in a container, long periods of storage at
normal temperatures can result in autosterilization and absence of viable microorganisms. Carbon
dioxide my be produced in sufficient quantities to swell the container. Storage at elevated temperatures
accelerates this action. Hydrogen can be produced in cans when the food contents react chemically with
the metal of the seam (3).

A. Equipment and materials

1. Fisher Model 1200 Gas Partitioner, with dual thermal conductivity cells and dual in-line
columns. Column No. 1 is 6-1/2 ft x 1/8 inch, aluminum packed, with 80-100 mesh
ColumpakTM PQ. Column No. 2 is 11 ft x 3/16 inch, aluminum packed, with 60-80 mesh
molecular sieve 13X (Fig. 1).

NOTE: Other gas chromatograph instruments equipped with the appropriate columns,
carrier gas, detector and recorder or integrator may also be suitable for this analysis.

Operating conditions: column temperature, 75°C; attenuation, 64/256; carrier gas, argon,
with in-let pressure of 40 psig; flow rate, 26 ml/min through gas partitioner and 5 ml/min
through flush line; bridge current, 125 mA; column mode, 1 & 2; temperature mode,
column; injector temperature, off.

NOTE: Installation of flush system. Injection of gas samples through either sample out
port or septum injection port may lead to damaged filaments in detector and excessive
accumulation of moisture on columns due to bypassing the sample drying tube. To avoid
this, make all injections in the sample in port. To avoid cross-contamination, install a flush
line off the main argon line (Fig. 2), and flush sample loop between injections.

2. Strip chart recorder, with full scale deflection and speed set at 1 cm/min, 1 mv

3. Can puncturing press (Fig. 3)

4. Sterile stainless steel gas piercers (Fig. 4)

5. Miniature inert valve, with 3-way stopcock and female luer on left side (Popper & Sons,
Inc., 300 Denton Ave., New Hyde Park, NY 11040), or equivalent (Fig. 5)

6. Plastic disposable 10-50 ml syringes, with restraining attachment for maximum volume
control (Fig. 6). Syringes may be reused.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 15 of 22

7. Gas chromatograph and caps, for capping syringes (Alltech Associates, Inc., 202 Campus
Drive, Arlington Heights, IL 60004), or equivalent (Fig. 6)

8. Beaker, 1 liter, glass or metal

9. Plastic gas tubing, 3 ft x 1/8 inch id, for exhaust tubing

10. Soap solution, for detecting gas leaks ("SNOOP" Nuclear Products Co., 15635 Saranac
Road, Cleveland, OH 44110), or equivalent

11. Small pinch clamp, to weigh down exhaust tubing in beaker

12. Nupro Valve, flow-regulating valve for flush line, 1/8 inch, Angle Pattern Brass (Alltech),
or equivalent (Fig. 2)

13. Silicone rubber tubing, seamless, red, autoclavable, 1/8 inch bore x 3/16 inch wall thickness
(Arthur H. Thomas Co., Vine St. at 3rd, Philadelphia, PA), or equivalent

B. Calibration of gas chromatograph

Calibration gases of known proportions are commercially available. Construct calibration curves
from analysis of pure gases and at least 2-3 different percentage mixtures of gases. Plot linear
graph of various known concentrations of each gas as peak height (mm) vs percent gas (Fig. 7).

C. Preparation of materials

Prepare gas collection apparatus as illustrated in Figs. 8 and 9. Adjust height of gas collection
apparatus to height of can to be examined. Attach male terminal of miniature valve to female
Luer-Lok terminal mounted on top of brass block on can-puncturing press. Attach one end of gas
exhaust tubing to female terminal of miniature valve. Attach small pinch clamp to other end of gas
exhaust tubing and place in beaker partially filled with water. Attach disposable syringe to other
female Luer-Lok terminal on miniature valve. Turn 2-way plug so that gas entering from piercer
will flow toward disposable syringe. Place sterile gas piercer in position on male terminal
mounted on bottom of brass block on can-puncturing press.

D. Collection of headspace gas

Place can under gas press (cans to be cultured should first be cleaned and sterilized). Lower
handle until gas piercer punctures can and seals. Hold in position until adequate volume of gas has
been collected (minimum of 5 ml); then turn 2-way plug to release excess gas through exhaust
tubing. Release handle, remove syringe, and cap immediately. Identify syringe appropriately.

E. Injection of gas into gas chromatograph

Turn on gas chromatograph and recorder. Let stabilize for about 2 h. Make sure flush line is
attached and gas sampling valve is open to allow flushing of sample loop. Turn on chart drive on
recorder. Remove flush line, uncap, and immediately attach syringe to Sample-In Injection Port.
Inject 5-10 ml of gas and immediately close gas sampling valve. Remove syringe and cap.
Reattach flush line onto Sample-In Port and open gas sample valve to allow flushing of system
before next injection. Observe chromatogram and switch attenuation from 64 to 256 after carbon

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 16 of 22

dioxide peak has been recorded and returned back to base line. This allows hydrogen peak to be
retained on scale. After hydrogen peak returns to base line, switch attenuation back to 64. After
instrument has separated gases (about 6 min), determine retention time and peak height for each
gas recovered from unknown sample and percent determined from standard graph by comparing
retention times and peak heights with known gases, usually associated with headspace gases from
abnormal canned food products. Mount chromatogram on mounting paper and identify properly as
in Fig. 10. For each sample examined, inject control gases for each type of headspace gas
recovered.

Figure 1. Fisher Model 1200 gas partitioner.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 17 of 22

Figure 2. Flush System.

Figure 3. Can puncturing press.

Figure 4. Stainless steel gas piercer.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 18 of 22

Figure 5. Miniature inert valve.

Figure 6. Plastic disposable syringe with restraining attachment.

Figure 7. Calibration graph for gas chromatography of headspace gas, using pure and unknown
mixtures.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 19 of 22

Figure 8. Gas collection apparatus.

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 20 of 22

Figure 9. Gas collection apparatus (detail).

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 21 of 22

Figure 10. Gas chromatograph of headspace gas.

References

1. Association of Official Analytical Chemists. 1990. Official Methods of Analysis, 15th ed. AOAC,
Arlington, VA.

2. Vosti, D.C., H.H. Hernandez, and J.G. Strand. 1961. Analysis of headspace gases in canned foods by
gas chromatography. Food Technol. 15:29-31.

3. Landry, W.I., J.E. Gilchrist, S. McLaughlin, and J.T. Peeler 1988. Analysis of abnormal canned
foods. AOAC Abstracts.

Hypertext Source: Examination of Canned Foods, Bacteriological Analytical Manual, 8th Edition,
Revision A, 1998. Chapter 21A.
Authors: Warren L. Landry, Albert H. Schwab, and Gayle A. Lancette

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Canned Foods Page 22 of 22

Top

B A M | B A M Media | B A M Reagents | Bad Bug Book

Foods Home | FDA Home | Search/Subject Index | Disclaimers & Privacy Policy

Hypertext updated by kwg 2001-JAN-05

mhtml:file://C:\Documents and Settings\Owner\My Documents\FSIS Canning Training\FS... 3/28/2008

FDA/CFSAN BAM - Examination of Glass Containers for Integrity http://www.cfsan.fda.gov/~ebam/bam-22b.html

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 22B
Examination of Containers for Integrity
II. Examination of Glass Containers for Integrity
Authors

(Return to Table of Contents)

Almost all low-acid foods packaged in glass containers are sealed with vacuum-type closures. Currently
4 types of vacuum closures are widely used on low-acid food products: LT (lug-type twist) cap, PT
(press-on twist-off) cap, pyr-off (side seal) cap, and CT (continuous thread) screw cap (Fig. 25).
Packers' tests and examinations to ensure a reliable hermetic seal of containers are required by 21 CFR
113.60 (a) (2) and (3).

Vacuum Twist Lug Finish Vacuum Pry Off Finish

Press On Twist Off Finish Continuous Thread Finish

Figure 25. Types of vacuum closures and glass finishes.

1 of 3 3/28/08 10:26 AM
FDA/CFSAN BAM - Examination of Glass Containers for Integrity http://www.cfsan.fda.gov/~ebam/bam-22b.html

A. Visual examination for closure and glass defects (for definition of terms, see the glossary section
of this chapter)

cap tilt
crushed lug
chipped glass finish
cut-through
cocked cap
stripped cap
cracked glass finish

B. Seal integrity examination

1. Vacuum. Use standard open-closed type of vacuum gauge or USG No. 12118 gauge with
both vacuum and pressure scales (Fig. 26). Wet rubber gasket on piercing device with
water. Shake off excess water. Puncture closure, using piercing needle attached to vacuum
gauge. Read and record vacuum in inches (0-30 inches), or pressure (0-15 psi).

Figure 26. Vacuum gauge for seal integrity examination.

2. Removal torque (cam-off) for PT or LT type closures (Fig. 27). Properly secure jar on
torque meter. Ease closures off in smooth, continuous motion rather than rapid, jerking
motion. Use one hand to twist cap counterclockwise to open cap from sealed jar while
avoiding any downward pressure on cap. Record maximum torque in inch-pounds required
to open cap.

Figure 27. Torque meter.

3. Security values (lug tension) on lug-type twist cap (Fig. 28). Make vertical line on cap
and corresponding line on container wall with marking pen. Turn closure counterclockwise
just until vacuum is broken. Reapply closure to container just until gasket compound

2 of 3 3/28/08 10:26 AM
FDA/CFSAN BAM - Examination of Glass Containers for Integrity http://www.cfsan.fda.gov/~ebam/bam-22b.html

touches glass finish and closure lug touches glass thread (or until closure is at 2 inch-pound
reapplication torque to achieve uniformity for application). Measure and record, in 1/16
inch increments, distance in front of vertical lines that were made before opening. Security
is considered positive if line on cap is to right of line on container, and negative if line on
cap is to left of line on container.

Figure 28. Security measurement for lug type twist closure.

4. Pull-up (lug position) for lug-type twist cap (Fig. 29). Mark vertical neck ring seam on
glass finish. Measure distance from this vertical line, in 1/16 inch increments, to leading
edge of cap lug position nearest it. Record lug position measurements made on right side of
vertical neck ring seam (as analyst looks at package) as positive (+) and those to left side of
parting line as negative (-).

Figure 29. Pull-up lug position of LTD measurement.

Hypertext Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. Chapter 22.
*Authors: Rong C. Lin, Paul H. King, and Melvin R. Johnston

Top

B A M | B A M Media | B A M Reagents | Bad Bug Book

Foods Home | FDA Home | Search/Subject Index | Disclaimers & Privacy Policy | Accessibility/Help

Hypertext updated by bap/kwg/cjm 2001-OCT-24

3 of 3 3/28/08 10:26 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 22C
Examination of Containers for Integrity
III. Examination of Flexible and Semirigid Food Containers for Integrity
George W. Arndt, Jr. (NFPA)
Author

(Return to Table of Contents)

Flexible and semirigid food packages are composed mainly or in part of plastic materials. Closure is
achieved by heat sealing or double seaming. The 4 main groups of packages that cause similar integrity
concerns and that are examined by common methods are paperboard packages, flexible pouches, plastic
cups and trays with flexible lids, and plastic cans with double-seamed metal ends.

The purpose of a hermetic closure is to provide a barrier to microorganisms and to prevent oxygen from
degrading the food. Closure integrity is significant because sealing surfaces may contain food particles
and moisture that contribute to heat-seal and double-seam defects. Critical control must be exercised in
this operation. Visual examination will reveal most defects. For many flexible packages, seal strength
may be ascertained by squeezing.

A. Package examination

Note condition of package (exterior and interior) and quality of seals or seams; observe and feel
for gross abnormalities, mechanical defects, perforations, malformations, crushing, flex cracks,
delamination, and swelling. Measure dimensions as recommended by manufacturer of closing
equipment or packaging material. Perform teardown procedure as described. Note condition of
package and closure. If there is evidence that a package may lose or has lost its hermetic seal, or
that microbial growth has occurred in the package contents, further investigation is required.

1. Visual examination

Use hand as well as eye. A magnifying glass with proper illumination is helpful. Rub
thumb and forefinger around seal area, feeling for folds and ridges. Rub fingers over flat
surfaces to feel for delamination, roughness, or unevenness. By sight and touch, determine
presence of defects. Mark location of defects with indelible ink. See Fig. 30 for visual
inspection criteria for closure seal.

1 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Figure 30. Visual inspection criteria for closure seal.

(Courtesy of Brik Pak, Inc.)

2. Examination of packages (see Tables 1 and 2)

Table 1. Test methods for plastic packages containing food (5)

Package type
Paper Flexible Plastic, Plastic, double-seam
Test methods board pouch heat-sealed lid metal end

Air leak testing O O O O

Biotesting O O O O
Burst testing O R R O
Chemical etching O O O NA
Compression, squeeze R O O O
testing
Distribution (abuse) O O O O
test
Dye penetration R O R O
Electester O NA NA NA
Electrolytic R O R NA
Gas leak detection O O O O
Incubation R R R R
Light NA O O O
Machine vision O O O O
Proximity tester O O O R
Seam scope projection NA NA NA R
Sound R NA R R
Tensile (peel) testing NA R R NA
Vacuum testing NA O R O
Visual inspection R R R R
Abbreviations: R, test method is recommended by NFPA Bulletin 41-L,
Flexible Package Integrity Bulletin; O, other commercially accepted test method applications;
NA, test method is inappropriate for this style package.

Table 2. List of visible package defects provided by National Food Processors Association (5)

2 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Package type(a)
Paper Flexible Plastic, Plastic, double-seam
Defect board pouch heat-sealed lid metal end

Abrasion + + + +
Blister - + - -
Burnt seal - - + -
Channel leak(er) - + + -
Clouded seal - + - -
Compressed seal - + - -
Contaminated seal - + + -
Convolution - + - -
Corner dent + - - -
Corner leaker + - - -
Crooked seal - + - -
Crushed + - + +
Defective seal - - + -
Deformed + - - -
Deformed seal + - - -
Delamination + + + +
Embossing - + - -
Flexcracks - + + +
Foreign matter - - + +
(inclusion)
Fracture - + + +
Gels - - + +
Hotfold - + - -
Incomplete seal - - + -
Label foldover - - + -
Leaker - + - -
Loose flaps + - - -
Malformed - - + +
Misaligned seal - - + +
Nonbonding - + - -
Notch leaker - + - -
Puncture + + + +
Seal creep - + - -
Seal leaker + - - -
Seal width variation - - + -
Shrinkage wrinkle - - + -

3 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Stringy seal - + - -
Swell (swollen + + + +
package)
Uneven impression - - + -
Uneven seal junction - + - -
Waffling - + - -
Weak seal + - - -
Wrinkle - + + -
a +, Definition is applicable to that package type; -, definition is not applicable.

a. Paperboard packages (20)

Teardown procedures. Unfold all flaps (except gable top packages); check integrity
and tightness of transverse (top and bottom) and side (vertical or longitudinal) seals
by firmly squeezing package. If package has longitudinal sealing (LS) strip, pull off
overlapping paper layer at side (longitudinal) seal. Check air gap of longitudinal
sealing strip application (about 1 mm). Squeeze package and check that there are no
leaks or holes in the LS strip.

Next, on side opposite side seal, puncture container with sharp scissors and empty
contents. Saving side seal portion, cut near fold at each end of package and down
length of package to remove a large rectangular body portion. Observe this large
rectangular body portion for holes, scratches, or tears anywhere on the surface. Pay
close attention to corners of package, particularly directly under end seals and near
the straw hole or pull tab, if present. Now cut remaining package in half through the
center of the side seam. Wash both halves of remaining package and dry them with a
paper towel. Mark to identify the package.

Evaluation procedures for seal quality differ between package designs, constructions,
and sealing methods. Obtain specific procedures for a given package from the
manufacturer. For example, seal evaluation may consist of starting at one end of the
seal, and very slowly and carefully pulling the seal apart. In some packages the seal
is good if the polymer stretches the entire length of the seal (that is, stretching of
polymer film continues to a point beyond which paper and laminates have separated).
In other packages, fiber tear can be seen the entire length of the seal (that is, raw
paperboard is visible on both sides of the separated seal areas). This is known as
100% fiber tear and indicates a good seal. Test all 3 seals of each package half.
Problems to look for are absence of (or narrow) fiber tear, lack of polymer stretch,
"cold spots" (no polymer bond in seal area), and "tacking" (polymer melt but no
stretch or fiber tear). For longitudinal sealing strip-type packages, additional tests
(such as centering examination, heat mark examination, and appearance of aluminum
foil examination when stripped) should be made according to manufacturer's
directions.

Electrolytic and dye testing. These tests differ according to each system
manufacturer's filed procedure. Contact the individual manufacturer, obtain
recommendations, and follow them.

b. Flexible pouches (20)

1. Teardown procedures. Check tightness of both head and side seals by

4 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

squeezing each package from each fill tube or sealing lane. Important points
are corners and crossing of head and side seals. This is a rapid determination
of obvious defects. Each seal must be accurately torn apart and evaluated for
correct integrity. Carefully inspect edges of each head and side seal for
evidence of product in seal areas. No product should be visible.

Observe width of each seal area. Width must comply with machine-type
specifications: for example, 1/16 inch minimum on all head and side seals for
fill tube or sealing lane machines. Look for presence of smooth seal junction
along inside edge of seal. Open each package to check side seals and head
seals. Visually inspect for such defects as misaligned seal, flex cracking,
nonbonding, and seal creep. If applicable, tear the seals by doing a seal tensile
strength test or a burst test. Then observe appearance of tear at each seal. Seals
should tear evenly so that foil and part of laminated layer from one side of
package tears off, adhering to seal on other side of package. The seal should
appear rough and marbleized. The seal is also adequate if the foil is laid bare
across entire length of seal. Retain records of test results as required.

2. Other test procedures

Squeeze test. Apply manual kneading action that forces product against
interior seal surface. The sealing surface must be smooth, parallel, and free of
wrinkles. Examine all seal areas for evidence of product leakage or
delamination. Packages that exhibit delamination of the outer ply on seal area
but not at product edge should be tested further by manually flexing the
suspect area 10 times and examining all seal areas for leakage or reduction in
the width of the seal area to less than 1/16 inch.

Seal tensile strength. Results to be expressed in pounds per linear inch,

average of sample (that is, 3 adjacent specimens cut from that seal) should not
be less than specified for the material and application.

Burst strength test. With internal pressure resistance as the measurement to

check all seals, apply uniform pressure, under designated test conditions, to a
level of not less than specified for a material or application, for 30 s. Then
evaluate seals to ensure that proper closure seal is still in effect.

c. Plastic package with heat-sealed lid (20)

Container integrity testing. Peel test procedures of form fill and seal containers.
Squeeze container side walls of entire set from a mold. Squeeze each cup to cause 1/8
inch bulge of lid area. Lid should not separate from package when package is
squeezed. Observe sealing area for fold-over wrinkles in sealant layer of lidstock.
From a first set of containers, visually observe embossed ring in sealed area for
completeness. (Embossed ring should be at least 90% complete if present.) Remove a
second set of containers (1 cup per mold) and gently peel back each lid at
approximately a 45 angle. Observe the peeled area for a generally frosty appearance
on both the lid and cup sealed surfaces. Observe entire package for holes, scratches,
even flange widths, smooth inside surfaces, and any deformities caused by dirty
mold or sealing die.

Leak test procedures (optional). These tests differ according to each system
manufacturer's filed procedure. Contact the individual manufacturer, obtain
recommendations, and follow them.

5 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Electrolytic test. Plastic packages generally do not conduct a flow of low-voltage

electricity unless a hole is present. Use a volt meter or amp meter to determine the
presence of a closed circuit. If a voltage flow can be measured, use a dye solution to
identify the presence of a hole.

Dye penetration test. Use a dye to locate leaks in packages or to demonstrate that
no leaks exist.

Air pressure or vacuum test. Apply pressure or vacuum to a closed package to test
for holes and to observe any loss of pressure or vacuum. Underwater vacuum testing
may reveal a steady stream of small bubbles emitting from a hole in a package.

d. Plastic cans with double-seamed metal ends (20)

Procedures for examining metal cans with double seams are described in Chapter 21
and in 21 CFR, Part 113. Use these methods to examine plastic cans with
double-seamed metal ends. Make the following changes to 21 CFR 113.60 (a,1,i,a
and b).

B. Micrometer measurement system

Metal cans. Required: cover hook, body hook, width (length, height), tightness (observation for
wrinkle), and thickness. Optional: overlap (by calculation) and countersink.

Plastic cans with double-seamed metal ends. Required in addition to seam scope examination:
thickness and tightness. Compare seam thickness to that calculated from individual thicknesses of
plastic flange and neck and metal end, excluding compound. Optional: cover hook, countersink,
and width (length, height).

Seam scope of projector

Metal cans. Required: body hook, overlap, tightness (observation for wrinkle), and thickness by
micrometer. Optional: width (length, height), cover hook, and countersink.

Plastic cans with double-seamed metal ends. Required: overlap, body hook, countersink,
width (length, height). Optional: cover hook.

Visual examination for plastic cans with double-seamed metal ends. Required: tightness.
Note compression of pressure ridge or flange during overlap measurement. Remove entire cover
and examine pressure ridge for continuity. Under 21 CFR 113.60 (a,1,i,c) add the following:
pressure ridge for plastic cans with double-seamed ends; impression around complete inside
periphery of can body in double seam area.

C. Microleak detection

Microleak testing methods are not listed in order of sensitivity, nor is it necessary to use them all.
Each test has advantages and disadvantages, depending on the package, equipment, and set of
conditions. Optional methods are appropriate when additional information will clarify the nature
of various package defects. Some test methods are not appropriate for some package materials,
closures, or package styles. Refer to the manufacturer of the package or closure system for
recommended test methods or see Table 1. Common methods are presented to provide the analyst
with procedures and options. Visible defects of the 4 flexible package groups are summarized in
Fig. 30.

Measure packages before testing for microleaks. Mark visually detected defects to aid location

6 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

during or after microleak testing (non-water soluble markers are recommended). Record all
results, methods used, and environmental conditions (temperature, relative humidity) and retain
these records. Conduct all tests in the standard laboratory atmosphere of 23 + 2°C and 50 + 5%
relative humidity. When this is not possible, report temperature and relative humidity along with
test results (14).

Figure 31. Air leak testing of packages.

1. Airleak testing (5) (Fig. 31)

a. Dry method

1. Materials

Compressed air with regulator

Needle, valve, hoses
Pressure gauge or flow meter

2. Procedure

Puncture container wall with needle. Inject air while increasing at 1 psi/s until a
standard pressure is reached. Standard pressure used for testing should be less
than the normal unrestrained burst pressure for the package. Observe pressure
gauge for loss of internal pressure over a 60 s period. If a flow meter is used,
observe for airflow, which indicates presence of openings in the test package.
Dye testing may be used to locate air leaks that are not visible with the dry
method. Inject air to create internal pressure within the package without
causing it to burst. Observe all surfaces and seals for air leaks. Observe flow
meter for indication of air loss from the package.

b. Wet method

1. Materials

Compressed air with regulator

Needle, valve, hoses
Water
Transparent container to observe bubbles

2. Procedure

7 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Inject air to create internal pressure within the package without causing it to
burst. Immerse package in water and inspect visually for a stream of bubbles
emitting from a common source.

c. Results

Positive. - A steady stream of bubbles comes from the package at one or more
locations.

Negative. - No bubbles are emitted from the package.

False positive. - Bubbles are emitted from point at which needle entered package; or
bubbles cling to surface of the package after package is submerged in water.

False negative. - Food particles block holes through which air might escape from
defective package; or air pressure used is insufficient to force air through minute
holes in package.

Figure 32. Biotesting of packages.

2. Biotesting (5,21) (Fig. 32)

The objective of biotesting is to detect the presence of holes in hermetic packages by

placing them in an agitated solution of fermentation bacteria in water for an extended period
of time.

Obtain representative packages and submerged them in an agitated solution of active

bacteria. The bacterial concentration should be >107/cm3. The temperature of the solution
that surrounds the packages should be maintained at a temperature that permits rapid
growth of the bacteria within any packages they may enter. However, growth of the
bacteria in the liquid surrounding the submerged packages is not desirable. The bacteria
must cause fermentation of the product within the package if they penetrate and must not be
pathogenic. Packages should be flexed during immersion to expose cracks and holes to
incursion. The solution that surrounds the packages should be maintained at a temperature
that permits rapid growth of bacteria within defective packages. After biotesting, packages
are incubated for 3 weeks at 95-100F. This test should be used only to evaluate new
package designs or to validate packaging systems. It should not be used as routine quality
control procedure. Other methods are cheaper, simpler, and just as reliable.

a. Materials

Water bath with temperature control and agitation solution of

Enterobacter aerogenes for foods, pH >5.0. Solution of
Lactobacillus cellobiosis for foods, pH <5.0
Sample packages
Apparatus to flex packages

8 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Incubator

b. Procedure

Obtain representative samples. Mix active bacteria in water at about 1.0 x 107/ml.
Immerse samples in mixture. Agitate water bath and flex sample for 30 min. Remove
packages and rinse with chlorinated water. Incubate samples for 2 weeks at 95-100F.
Observe packages for swelling for 3 weeks. Open each package by cutting in half
across the middle, leaving a hinge and observe contents for spoilage. Thoroughly
wash insides of both halves from each spoiled package. Subject each half to a dye
test to locate leaks.

c. Results. Report location of leaks.

Figure 33. Burst tester.

Figure 34. Pouch air burst tester.

3. Burst testing (5) (Figs. 33 and 34)

The objective of burst testing is to provide a means for determining the ability of a
hermetically sealed package to withstand internal pressure (psig). The entire package is
subjected to uniform stress and failure generally reveals the weakest point. Both restrained
and unrestrained burst testing may be used. Restraint limits expansion by minimizing the
angle of the package seal, which becomes greater as a package is inflated. With restraint,
packages with strong seals fail at greater internal pressure than do packages with weak
seals. Thus, use of a restraining device during burst testing permits noticeable separation
between packages having strong or weak seals.

Fused seals are stronger than the walls of a flexible package. Burst failure generally occurs
adjacent to fused seals. Peelable seals are weaker than the walls of a flexible package, and
less pressure is needed to induce pressure failure. Lower pressure and a longer time
increment are required to burst test peelable seals.

Dynamic burst testing involves a steady increase of internal pressure until failure occurs.

9 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Static burst testing involves a steady increase in internal pressure to a pressure less than
failure, followed by a 30-s hold. Both methods are used for packages with fused seals.
Peelable seals are burst-tested by inflating at a steady rate to a point less than failure
pressure and held for 30 s, followed by a 0.5 psig pressure increase and another 30-s hold.
Pressure and time indexing is continued with observation of the seal area for seal separation
(peeling) until failure occurs.

a. Materials

Compressed air or water

Regulation valve
Needle with gasket and pressure tubing
Solenoid with timer(s)
Pressure indicator(s), digital or gauge with sweep hand
Restraining device (optional)

b. Procedure

Use empty sealed package, or cut and remove contents of a filled package. Place
package in restraining fixture (if used). Pierce package with gasketted needle(s) and
inject air or water. Inflate at 1 psig/s.

Dynamic method. Continue inflation at 1 psig/s until failure occurs. Record internal
pressure at failure.

Static method. Inflate at 1 psig/s to specified internal pressure, and hold at specified
pressure for 30 s. Record as pass or fail.

Indexed method. Inflate to 5 psig and hold for 30 s, inflate additional 0.5 psig and
hold for 30 s. Continue increase and hold sequence until failure occurs. Observe
peelable seal separation. Report internal pressure at failure.

c. Results

Positive. Pressure failure occurs below specified level of performance, indicating a

hole in the package.

Negative. No pressure failure occurs below specified level of performance.

False positive. A leak is present at point where air or water is injected into package
and pressure cannot be maintained.

False negative. A small leak occurs, but is not sufficient to reduce pressure
noticeably.

4. Chemical etching (5)

Multilaminate and composite packaging materials may be etched to remove overlying

layers, revealing the hermetic seal of packages that have polyolefin heat seals. This allows
comparison of visually detected package defects on the external surface before etching and
within the seal area after all external layers have been removed.

Composite paperboard packages. The outer layers of a package are removed by tearing,
abrasion, and chemical action to expose the sealant layer intact. By photographing or
photocopying the package before etching, the etched seal can be compared with the

10 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

photograph to determine the significance of visually discernible defects.

a. Materials

Water bath and heater with thermostat

Three l-L Pyrex glass beakers
Running tap water
Graduated cylinder
Automatic stirring device (heated is preferred)
Drying oven equilibrated to 65°C (150F)
Paper towels
Rubber gloves, protective goggles, apron, tongs
Fume hood with chemical-resistant surface

Chemicals for etching of paperboard aseptic packages:

hydrochloric acid (HCl) solution, 3.7 N
acidified solution of copper chloride (CuC12)
saturated solution of bisodium carbonate (Na2CO3) in water

b. Preparation of solutions. CAUTION: Always pour acid into water; never pour
water into acid.

Pour 0.5 L of concentrated HCl into 1 L of cold distilled water. Pour slowly, as heat
will be produced when acid and water mix. Stir until mixed completely. Cover to
prevent evaporation. Solution will be 3.7 N HCl.

Pour 0.5 L of concentrated HCl into 1.5 L of cold distilled water. Add 10 g of
CuC12. Stir until completely mixed. Cover beaker and let warm to room temperature
before using.

Pour enough Na2CO3 into a container to make a saturated solution at room

temperature. Some undissolved Na2CO3 should remain on bottom of beaker after
stirring.

c. Procedure

Cut transversal seal from package approximately 1 inch from end. Identify multiple
samples by notching cut edge with scissors. Manually strip paper from sample to be
etched. Place sample in hot HCl solution (65°C) for 5 min. Remove sample with
tongs and immerse it in Na2CO3 solution to neutralize the acid. Remove sample from
the Na2CO3 solution with tongs and rinse it in running tap water. Pull off
polyethylene layer that lies between paperboard layer and aluminum foil.

Using a glass stirring rod to manipulate the sample, drop it into the CuC12 solution
so that it is completely immersed. Observe closely while stirring to ensure that the
heat of the reaction does not damage the polyethylene sealant layer as the foil is
dissolved. Remove from solution.

Dip sample in Na2CO3 solution to neutralize it, and then rinse it with water. Press
sample gently between soft absorbent paper towels and place in oven at 65°C (150F)
until dry. Apply alcohol-based dye solution to inner and outer seal edges. (See
fluorescein dye solution formula, described above).

11 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Observe pattern of ink dispersion and check for leaks and channels within fused seal
area. Use overhead projector to enlarge seal samples and provide a more accurate
visual inspection.

Figure 35. Chemical etching of package seal.

Retortable pouches (Fig. 35)

1. Materials

Two l-L Pyrex beakers

Running tap water
Paper towels
Rubber gloves, apron
Protective goggles, tongs
Fume hood with chemical-resistant surface
Chemicals for etching retortable pouches
6 N HCl solution, commercial grade
Tetrahydrofurant (THF), commercial grade, stabilized

2. Procedure

Cut off end of pouch and remove contents. Wash inside of pouch. Dry the pouch.
Cut all but suspected area away from area of interest, leaving about 1 inch adjacent to
seal. Soak sample in tetrahydrofurant (THF) to remove outer polyester layer by
softening adhesive and/or inks. Do this in a fume hood; wear protective gloves
resistant to THF. (If separation cannot be obtained, proceed to next step.) Remove
most of the ink and adhesive from aluminum foil with THF and paper towels. Soak
remaining structure in 6 N HCl in a fume hood to remove aluminum foil by etching.
Rinse sealant layers with water and dry with paper towels.

Figure 36. Compression testing of packages.

12 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

5. Compression test (5) (Fig. 36)

Place a filled and sealed food package on flat surface and apply pressure while observing
for leaks.

a. Materials

Flat surface or conveyor belt

Sealed package
Heavy flat object or mechanical press
Timer

b. Procedure

Static method. Place sealed package on flat surface and lay a flat-surfaced weight on
it. Observe effect of weight on integrity of package seals over time. A similar test
may be performed by applying a constant weight to a package moving on a conveyor
belt. The speed of the moving belt determines the time of compression.

Dynamic method. Use a press to continually increase the force applied to a package
at a constant rate. Observe the maximum force required to cause failure of the
package.

Squeeze test. Apply a manual kneading action that forces product against the interior
seal surface area. Examine all seal areas for evidence of product leakage or
delamination. Packages that exhibit delamination of the outer ply on the seal area but
not at product edge should be tested further by again manually flexing the suspect
area 10 times and examining all seal areas for leakage or short-width.

c. Results

Positive. Holes form in package or its seals or seams, with measurable movement of
top plate or deflection on a force gauge.

Negative. No loss of hermetic integrity, and no measurable movement of top plate or

deflection on a force gauge.

False positive. Underfilled or weak packages deflect in a manner that simulates

failure without loss of hermetic integrity.

False negative. Holes form in package but food product closes off the holes,
permitting pressure to increase within package.

6. Distribution (abuse) test (5)

Packages are subjected to vibration, compression, and impact at levels typical of the
distribution system for which they are designed. After the test, which is a conditioning
regimen, the packages are examined. Defects are quantified and described in relation to
package failures observed in normal distribution. Fragility is eliminated by design changes
in the package system. Whenever possible all samples should be incubated for 2 weeks at
100F before abuse-testing (Fig. 37).

13 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Figure 37. Distribution abuse testing.

a. Materials

Packages to be tested
Drop tester
Vibration table
Compression tester
Standard laboratory conditions 23 + 2°C, 50 + 5% relative humidity
Incubator at 100F to contain all test packages

b. Procedure. See ASTM D-4169 Standard Practice for Performance Testing of

Shipping Containers and Systems (15).

Select distribution cycle 6 for flexible packages in shipping cases transported by

motor freight. Before testing, incubate all packages for 14 days at 100F and inspect
visually for defects.

Perform the following 10 steps (see Section 9 of ASTM D-4169) (15).

1. Define shipping unit - Shipping unit to be tested is a typical pallet load.

2. Establish assurance level - Assurance level II will be used, based on value and
volume of shipment.

3. Determine acceptance criteria at assurance level II: Criterion 1 - no product

damage; criterion 2 - all packages in good condition.

4. Select distribution cycle (DC) - DC-6 will be used for pallet shipments.

5. Write test plan (values for X must be determined before conducting the test).
Select representative samples for test. Condition samples to 23 + 1°C, 50 +
2% relative humidity, in accordance with Practice D 4332 (14).

6. Perform tests in accordance with test plan in step 5, as directed in the

referenced ASTM standards and in the special instructions for each shipment.

7. Evaluate results - Examine products and packages to determine if acceptance

criteria have been met.

8. Document test results (16) - Write a report to cover all steps in detail.

9. Report fully all the steps taken. At a minimum, the report should include all the
criteria in step 10.

10. Description of product and shipping unit DC and test plan Assurance levels

14 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

and rationale
Number of samples tested
Conditioning used
Acceptance criteria
Variation from recommended procedures
Condition of specimens after test

After testing, examine all failed (positive) packages to determine location and
cause of damage. Incubate all containers that do not fail (negative) during
testing for 14 days at 100F and inspect visually for defects before destructive
testing by other methods listed in this chapter.

c. Results

Positive. A package loses hermetic integrity during any one phase of the testing
protocol or during the incubation period that follows.

Type test ASTM Level

Method

Handling (12) D-1083 One impact on 2 opposite base edges from X inches

Stacking (10) D-642 Compression to X lb (individual container) *

Vibration (13) D-999 Search 3-100 Hz at 0.5 g peak. Dwell 10 min at 0.5 g peak
Method C

Handling (11) D-959 One impact on 2 opposite base edges from X inches

(12) D-1083

(17) D-997

(18) D-775

Stacking (10) D-642 Compression to X lb (individual container) *

*Alternative full pallet load compression test, X lb per bottom tier container.

Negative. A package retains hermetic integrity through the test, and contents do not
show evidence of microbial growth after incubation.

False positive. A package appears to be defective, yet confirmational testing by

incubation or dye penetration reveals that no loss of the hermetic barrier occurred
during the abuse test.

False negative. A package appears to pass testing but later exhibits failure when
incubated.

7. Dye testing (5)

15 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Dye or ink is applied to inside surface of a cleaned package at the seal or suspected location
of failure and observed to determine whether it can pass through to the outside (Figs. 24,
38, 39).

Figure 24. Can piercer and gas collection apparatus.

Figure 38. Dye testing.

Figure 39. Dye testing results.

(Courtesy of Brik Pak, Inc.)

a. Materials

Disposable plastic gloves

Dye solution: 1 L of isopropanol (solvent) and 5 g of rhodamine (powder) mixed (or
other appropriate dye solution)
Sink
Scissors or knife
Oven to dry sample packages
Paper towels
Magnifying glass or low-power microscope

b. Procedure

Open and empty a package; wash, and dry by wiping or by oven drying (180F, 15
min). Apply low surface-tension solution containing dye along the closure or on side
of package at suspected location of hole. The solution moves by capillary action
through the hole and appears on opposite side of package wall. After dye is
completely dry, cut package with scissors and examine the hole closely.

16 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Cut open cans, tubs, or bowls through bottom (leaving seal areas or double seams
untouched) and remove product. Cut pouches and paperboard containers along
equator, leaving a hinge (so that both ends can be tested), and remove product. Wash
package with water containing mild detergent, rinse thoroughly with tap water, and
wipe dry. Holding package upside down and at slight angle, place 1 drop of dye
solution at inside edge of seal surface. Rotate to allow dye to wet entire inside seal
circumference.

CAUTION: A number of dyes are known or suspected to cause cancer. Rhodamine

B is a possible carcinogen. Wear disposable plastic gloves and avoid skin contact
with dyes.

Let dye solution dry completely. Very slowly peel the seal completely and observe
the frosty, white, sealed surfaces for evidence of dye. In some packages the
innermost laminates must be carefully observed for stretching as the seal is peeled.

c. Results

Positive. Dye penetrates hole in package, indicating loss of hermetic barrier.

Negative. Dye does not pass through the package (wall or seal).

False positive. Solution dissolves packaging material, creating hole in package, or

dye is accidentally splattered on outside of package, indicating hole or leakage where
none exists.

False negative (for paperboard only). Solution penetrates holes in hermetic barrier
layers but fails to reach outside of package where it would be visible.

8. Electester (5)

The objective is to determine changes in viscosity of liquid foods after incubation of filled
packages (Fig. 40).

Figure 40. Electester

Microbial fermentation can cause changes in the viscosity of still liquids. If all factors are
constant, shock waves will dampen at different rates in liquids with different viscosities.
Incubation of shelf-stable liquid foods and nondestructive testing of each package may
identify containers that have been subjected to microbial activity.

a. Materials

Packages filled with still, liquid food, incubated

Electesting device
Fixture to restrain test packages

17 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

b. Procedure

Remove representative samples from production line and incubate at 95°F for 4 days.
Place packages containing still liquids in restraining device with largest flat surface of
package facing downward. Rotate package 90 horizontally and back to its original
position very rapidly; do this only one time. The motion creates a shock wave.
Fixture holding the package is precisely balanced to minimize outside interference
and minimize dampening as shock wave moves back and forth within package.
Motion is sensed and displayed on an oscilloscope with alarms alerting operator to
vibrations that dampen more quickly or more slowly than normal for a specific liquid
food product. Examine contents with a microscope and determine pH to confirm
spoilage if there is any doubt.

c. Results

Positive. Wave dampens more quickly or slowly than normal, indicating change in
product viscosity.

Negative. Rate of wave dampening is within range established by testing "normal"

liquid product that did not display microbial spoilage during incubation.

False positive. Range of acceptance is too narrow, and normal product is incorrectly
identified as spoiled.

False negative. Range of acceptance is too broad, and spoiled product is incorrectly
identified as normal.

9. Electroconductivity (5)

The objective is to detect holes in hermetic packages by sensing the flow of electrical
current. Plastics are generally poor conductors of electricity. Consequently, plastic food
packages without holes will form an effective barrier to mild electrical current; therefore,
this method may be used to detect minute breaks in plastic food packages. A detectable
flow of low-voltage electrical current generally indicates that the hermetic barrier has been
lost.

a. Materials

1% NaCl in water (brine solution)

Scissors
Battery 9V, three 12-inch lengths of wire, 9V light bulb, or a conductivity meter
(VOM). Remove insulation from each end of wires. One wire from positive pole
goes to light bulb that has a wire as probe. The second wire from the negative pole is
the other probe (Fig. 41).
Plastic bowl large enough to submerge package

Figure 41. An electrolytic cell for leak examination.

18 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

b. Procedure

Obtain sample food package and cut off one end with scissors. Aseptic paperboard
packages and flexible pouches may be cut on all but one edge along package equator
and folded 180 on uncut side to form 2 equal halves. Wash samples to remove all
food contents and any dried plugs that may occlude holes. Oven drying at 180F is
recommended but not required before immersion. Wipe the cut edges with a paper
towel if necessary, as wet edges may result in false-positive test results. Place
samples in bowl containing brine solution and partially fill sample with brine so that
it stands upright and is almost completely submerged. Place conductivity meter or
light bulb with one probe inside the package and the other outside the package.
Submerge both probes into their respective brine solutions. Test the other half of
package similarly for current flow.

c. Results

Positive. Current flow indicates break in hermetic barrier.

Negative. No current flow indicates hermetic barrier exists.

False positive. Aluminum foil conducts electricity. A pinhole or partial break

through inner layers of a package may expose the foil layer, resulting in
false-positive test result. Dye testing will confirm presence or absence of holes.
Moisture may form a bridge over cut edge of a package, creating a false
positive.False negative. Dried product may occlude minute holes in a package. If
plugs do not rehydrate quickly, they will not conduct electricity when packages are
immersed.

10. Gas detection (5)

The objective is to detect microleaks in hermetically sealed packages with sensors tuned to
detect only gas leaking from within package. The package must be a barrier to the test gas
so that the rate of gas permeation through the package wall will not raise the normal
background concentration in atmosphere of testing area. Gas concentrations may be
detected by impact to a sensor. The sensor may be a heated element in which electrical
resistance varies in relation to gas molecules removing heat as they impact. Examples of test
gases suitable for package include oxygen, nitrogen, hydrogen, carbon dioxide, and helium.

a. Procedure for detecting helium leak

Gas obtained from storage tanks or air fractioning may be used to displace headspace
gases within food packages before closure. Concentration of gas within package
must be greater than the concentration of that gas in the atmosphere where packages
are tested. There are three modes for detection: ASTM E493, inside-out tracer mode
(6); ASTM E498, tracer probe testing mode (7); and ASTM E499, detector probe
testing mode (8). Slight compression of a package may assist the movement of gas
molecules through microleaks.

b. Results

Positive. Detection of gas concentrations greater than the normal atmospheric

concentration indicates break in hermetic barrier of sample package. Confirm with
dye testing to locate hole in sample package.

Negative. No detection of test gas concentration greater than the normal atmospheric

19 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

concentration indicates hermetically sealed container.

False positive. Detection of gas concentrations in excess of the normal background

level may result from increase in test gas concentration in the testing area. Test
background concentration before and after testing sample. Packages with high
permeability may lose gas.

False negative. Internal gas concentration may be reduced through absorption by the
product, reaction with a component inside the package, or permeability if over an
extended storage period.

11. Incubation (5)

The objective is to determine whether a package has lost hermetic barrier by holding
containers at an ideal temperature for sufficient time to ensure microbial growth. Hermetic
integrity is the condition that bars entry of microorganisms into a package. Growth of
microorganisms indicates either insufficient processing or loss of hermetic barrier. Growth
may be observed as gas formation, change in pH, growth of viable organisms, or changes
in the appearance of food.

a. Materials

Insulated box or room to serve as an incubator

Heater with thermostat
Storage racks
Recording thermometer
Temperature recording charts
Knife, scissors
pH meter
Inoculating loop and flame
Sterile culture dishes and tubes, and culture media

b. Procedure

Obtain representative sample packages containing processed product. Inspect all

samples visually for defects. Place packages in incubator for recommended period of
time at recommended temperature.

Products stored in incubator at 95°F (35°C)

FDA products - 14 days
USDA products - 10 days
Products stored in warehouse
85-95°F (29-35°C) 30 days
70-85°F (21-29°C) 60 days
60-70F (16-21°C) 90 days

Visually inspect packages for evidence of spoilage. Open and inspect all (or some)
packages for visible signs of microbial growth, aroma, and change in pH. Never taste
incubated product if spoilage may have occurred. Aseptically obtain product samples
to culture microbiologically and confirm cause of spoilage. Conduct appropriate
integrity test on package to identify presence or absence of microleaks. Dispose of
product safely. Autoclave any product or packages showing spoilage before
disposal.

c. Results

20 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Positive. Spoilage has occurred and is evident as swelling, putrefactive odor, change
in product pH from normal, or change in appearance.

Negative. Spoilage has not occurred.

False positive. Chemical reaction or enzymatic activities alter product characteristics

without microbial activity.

False negative. Should not occur because this would be commercial sterility.

12. Light (5)

a. Infrared light. The objective is to observe differences in the absorbance and

transmittance of heat energy (infrared light) in a package or seal. Infrared light may
be absorbed, transmitted, and emitted by a package or a seal. Differences between
these parameters provide a means for visual interpretation when sensed automatically
and enhanced for visibility.

1. Materials

Infrared light or oven (180F)

Visual infrared light detector

2. Procedure: Expose samples to infrared radiation before examining.

b. Laser light. The objective is to measure small changes in the relative position of
similar surfaces on separate packages as they are subjected to changes in external
pressure. Flexible packages possessing some headspace gas may be flexed by
altering the external pressure in a closed chamber. Packages are held by fixtures so
that a split laser beam may be directed to the same position on both packages. The
reflected beams are recombined with mirrors and prisms. Laser light has a
well-defined wave length that does not change by reflection. However, if packages
move differently when flexed, one beam segment will travel a greater distance than
the other. When beam segments are recombined, differences in position of reflecting
surfaces will cause the recombined laser beam to be out of phase. This condition can
be sensed and used to segregate packages that do not flex in the normal manner from
those that do.

1. Materials: Laser set up with chamber and means to read the differences.

2. Procedure: Flex packages in chamber by applying and releasing vacuum.

Observe any difference in the 2 packages and determine by controls which
package leaks.

c. Polarized light. The objective is to observe differences in the transmittance of visible

light through translucent and transparent heat seals (Fig. 42). Polarized light filters
are composed of minute parallel lines on a glass surface or plastic film. When 2
polarized filters are rotated to be 90 different, no light will pass through. At 0, both
sets of lines are parallel and a light bulb set in line with the 2 polarized filters will be
visible.

21 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Figure 42. Visual inspection of transparent seals with polarized light.

During heat sealing of transparent and translucent plastic materials, energy is added,
providing free movement of polymer chains. Close packing and increased hydrogen
bonding occurs, resulting in alignment of carbon chains and increased crystalline
structure. Differences between random, oriented, and crystalline configuration affect
both light absorption and transmission in these materials. A seal sample placed
between 2 polarizing filters is first illuminated by polarized light. To enhance color
changes resulting from differences in crystalline structure, rotate the other filter to
block most of the transmitted light. Inspect visually to determine degree of
crystalinity within fused seals. Uniform crystalinity, seen as uniform color tone along
the inner edge of the primary seal, is one indicator of fusion. Areas that are not fused
appear as a different color. Colors differ with materials and thickness.

1. Materials

Light bulb, white, 40, 75, 100 W

Polarized camera filters, 2 each
Frame to hold filters and permit free rotation of both
filters in line with light bulb and sample

2. Procedure

Obtain a clean transparent seal sample. Turn on light. Place seal sample
between polarized filters. Rotate one filter to obtain maximum difference in
color between fused seal and nonseal area. Examine fused seal area for
uniformity.

d. Visible light. The objective is to detect holes in packages by sensing transmitted and
reflected visible light. Package is placed over low-wattage light bulb in darkened
room to enhance visual inspection. Aluminum foil will block all light transmission
except where holes and flexcracks in foil are present. Close inspection is required to
determine whether other lamina overlay holes in foil layer. Dye testing is required to
establish presence or absence of minute holes. Chemical etching may be used to
remove materials external to polyolefin seals. Magnification of etched seals with
backlighting aids inspection.

1. Materials

Light bulb
Scissors
Sink with running water
Paper towels
Darkened room
Indelible marking pen
Dye (optional)

2. Procedure

22 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Remove contents, wash, and dry container. Inspect package for light leaks.
Mark location of light leaks with a marking pen; draw a circle around the
defect location. Closely examine defects for presence of holes through all
layers. Use dye test to verify presence or absence of holes.

3. Results

Positive. A hole through all layers is detected in a package.

Negative. No light leaks are detected.

False positive. A hole in the foil layers permits light to pass, but no holes exist
in overlying layers and hermetic barrier is maintained.

False negative. A hole through all layers is not aligned so that light can be
transmitted.

13. Machine vision (5)

The objective is to detect holes in hermetic packages by computer evaluation of images with
previously defined patterns of acceptance. This system is designed to eliminate visual
inspection of packages. Packages are positioned before a camera to present a consistent
pattern. The video image obtained is digitized. Both grayscale and color density may be
evaluated. The computer compares coded patterns with acceptable patterns stored in
memory. Some systems evaluate one image at a time. Others use parallel computers to
evaluate different segments of the video image in less time. Patterns that do not match the
acceptance criteria are rejected and the package is automatically rejected from the production
line.

a. Materials

Video imaging system

Computer with stored images for acceptance criteria
Strobe light (optional)
Packages

b. Results

Positive. Image does not match acceptance criteria.

Negative. Image matches acceptance criteria.

False positive. Image was not presented to camera correctly and does not match
acceptance criteria.

False negative. Acceptance criteria include defects.

14. Proximity devices (5)

The objective is to detect holes by measuring changes in the shape of hermetically sealed
packages as a function of time. The position of a package containing metal may be
established by the strength of a magnetic field, detected with a galvanometer. By comparing
2 readings as a function of time, a determination can be made as to whether the shape of a
package has changed.

23 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

a. Materials

Proximity detection system

Computer with stored acceptance criteria
Packages

b. Procedure

Compare multiple packages to a standard value. Fix limits of acceptance or alter

automatically by computing a running average and standard deviation. Packages
displaying stronger or weaker disturbances to a magnetic field sensed by a
galvanometer may fall outside of the limits of acceptance. Mark these packages for
removal from packaging line.

Read magnetic fields of single packages at one location and, after a period of time,
make a second reading at a downstream location. If shape of container changes, mark
package for removal from packaging line. Confirm with dye testing to locate holes in
packages.

c. Results

Positive. Disturbance of magnetic field exceeding limits of acceptance.

Negative. Disturbance of magnetic field within limits of acceptance.

False positive. External disturbance of magnetic field or imprecise positioning of

package resulted in values that exceeded limits of acceptance.

False negative. Distortion of package sufficient to cause disturbance of magnetic

field outside normal range of acceptance.

15. Seam scope projection (5)

The objective is to measure critical dimensions in the closure profile of plastic packages.
Packages are cut in cross-section to reveal all components in their proper thickness and
relative position. The cut edge is magnified with a projector to aid measurement and visual
inspection.

a. Materials

Knife, saw, or scissors

Microprojector
Micrometer, calipers, ruler, or measurescope

b. Procedure

Cut directly across seal or closure with knife, saw, or scissors and remove section
containing adjacent material. Magnify cross section. Compare observed dimensions
with criteria for acceptance or rejection provided by manufacturer of package or
closure machine. Accept or reject sample.

c. Results

Positive. Dimensions of sample exceed limits of criteria for acceptance.

24 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Negative. Dimensions within limits of criteria for acceptance.

False positive. Magnification with incorrect scale or measuring error results in

rejection of acceptable sample.

False negative. Measuring error results in acceptance of defective sample.

16. Sound (5)

Ultrasonic. The objective is to passively sense air moving through small orifices in
packages possessing internal vacuum or pressure by monitoring the presence or absence of
high-frequency sound waves.

a. Materials

Microphone
Audiofilters
Oscilloscope with alarm system
Packages

b. Procedure

Place packages in a chamber to eliminate external disturbances and subject to changes

in external pressure. Air movement through small holes in package wall generates
ultrasonic sound waves. A microphone senses the vibration. Audiofilters eliminate
all frequencies except those of interest.

c. Results

Positive. Package exhibits ultrasonic whistling sound, indicating a leak is present,

permitting air to enter or exit package.

Negative. No sound is emitted by package within range of frequencies monitored.

False positive. Background noise occurred within range monitored.

False negative. Hole does not emit a noise within the range monitored, or hole was
occluded by moisture or food.

Echo. The objective is to actively sense the frequency of echoes in hermetically sealed
containers. When a package possessing a vacuum is tapped, the tightness of the package
creates a sound that is audibly different from that of the same package without a vacuum.
Two changes can be monitored: frequency and amplitude. Changes in frequency (vibrations
per second) are recognized as differences in tone (pitch). Changes in amplitude are
recognized as 2 relative difference in volume. Loss of hermetic integrity will result in
microbial growth within the contents of a food package during incubation. Changes in
sound accompany changes in viscosity. Consequently, this method may be used as a
nondestructive test for a number of product/package combinations.

a. Materials

Control sample
Samples to be evaluated
Tapping device (electronic device or unsharpened pencil to be used like a drumstick)
Incubator

25 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

b. Procedure

Obtain sample packages, either newly packed or incubated, and a control package
(known to be properly sealed) containing the same product as sample packages. Tap
the section of the package covering that is taut. Listen to the echo for differences
between packages. Commercial devices are available that electronically monitor the
echos, allowing for a less subjective determination.

c. Results

Positive. Package displays audibly different sound, indicating loss of hermetic

integrity.

Negative. Package resonates at same frequency as control package.

False positive. Differences in vacuum level or fill volume create different sounds in
test packages.

False negative. Audible difference between control package and test package cannot
be differentiated.

17. Tensile strength (5)

The objective is to measure the tensile strength required to cause separation of peelable or
fused seals. A section of a seal is obtained by cutting a 1/2 or 1 inch strip perpendicular to
the seal edge. The strip is then clamped by opposing grippers and pulled at constant speed
and defined angle until failure is obtained. The peak force required to fully separate the 2
halves is recorded as the strength of the seal.

a. Materials

Sample packages
Sample cutting apparatus
Scissors (sample dimensions are critical to precision)
Tensile strength testing device

b. Procedure. See ASTM D-882 - Standard test methods for tensile properties of thin
plastic sheeting (9).

Remove representative sample from production line. Cut open sample and remove
contents. Do not disturb seal to be tested. Cut a segment of the seal to produce a test
strip. Test strip must be cut perpendicular to the seal to be tested. Secure both ends of
test strip in separate clamps. With screwdriver, move one screw clamp away from the
other, creating a 180° separation of the seal. Observe force required to fully separate
seal. Fixtures are required to hold samples at angles different from 180°.

c. Results

Positive. Sample separates at peak tensile strength less than established standard.

Negative. Sample separates uniformly at peak tensile strength greater than or equal to
established standard.

False positive. Sample separates at peak tensile strength less than established
standard because of equipment miscalibration or greater separation speed of jaws.

26 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

False negative. Sample separates at tensile strength greater than or equal to

established standard. However, a different portion of the same sample failed at a
tensile strength less than the standard.

18. Vacuum testing (5)

The objective is to cause the movement of air out of a sealed container through leaks by
using external vacuum within a testing chamber. Closed packages are placed inside a sealed
testing chamber and vacuum is created to cause movement of air through leaks in the
packages. Deflection of the package may be measured as a function of time to determine
whether leakage has occurred. If vacuum chamber contains water, bubbles from holes in
packages may be observed.

a. Materials

Bell jar (glass or plastic) with tight-fitting lid

Water to cover package within bell jar
Weighted fixture to keep package below water level during test
Vacuum pump
Vacuum gauge
Valve
Grease for tight gasketing of lid on chamber

b. Procedure

Obtain representative sample from production line. Place one sample inside vacuum
chamber. Evacuate chamber. Observe package swelling and any movement of air
(bubbles) or product through holes that may be present or may have developed.
When vacuum is released, observe packages to determine if original shape is retained
or if atmospheric pressure causes sample to appear slightly crushed.

c. Results

Positive. Leak in test package causes air or product to escape through holes in
container. Container ruptures or lid separates because of weak closure. When
vacuum is released, package appears distorted or crushed by atmospheric pressure.

Negative. Package distorts under vacuum but no loss of product or air is observed.
When vacuum is released, package assumes its original configuration.

False positive. Air clinging to surface of package or within paper laminates is

mistaken for bubbles emitting from a defect.

False negative. Food particles prevent movement of air out of a hole in container
while under vacuum.

19. Visual inspection (5)

The objective is to visually observe defects in food packages. Representative samples are
obtained from production line. External surfaces are examined for holes, abrasions,
delamination, and correct design. Critical dimensions are measured and observations
recorded.

a. Materials

27 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Flexible and Semirigid Food... http://www.cfsan.fda.gov/~ebam/bam-22c.html

Strong light without glare, for visual inspection of packages

Measuring devices, such as ruler, calipers, micrometer
Scissors or knife

b. Procedure

Refer to examination procedures for paperboard packages, flexible pouches, plastic

packages with heat-sealed lids, and plastic cans with double-seamed metal ends.

c. Results

Positive. Visually detected defect.

Negative. No visually detected defects.

False positive. Visual identification of defect not actually present.

False negative. Defect is present, but not visually detected.

Acknowledgments

We thank the American Can Co. for permission to include various useful items of information. We are
grateful to Donald E. Lake, George A. Clark, and Arnold A. Kopetz of American Can Co. for assisting
our development of this project in their laboratories.

We also thank the following individuals for reviewing the manuscript and contributing many valuable
suggestions: Keith A. Ito, National Food Processors Association; Raymond C. Schick and Robert A.
Drake, Glass Packaging Institute; Irvin J. Pflug, University of Minnesota; Fred J. Kraus, Continental
Can Co.; Robert M. Nelson, W.R. Grace & Co.; Don A. Corlett, Jr., Del Monte Corp.; Harold H. Hale
and J. W. Bayer, Owens-Illinois; Charles S. Ochs, Anchor Hocking; Rachel A. Rosa, Maine Sardine
Council; Melvin R. Wadsworth, Consultant; Tedio Ciavarini, U.S. Army Natick R&D Laboratories;
Robert A. Miller, U.S. Department of Agriculture; Helen L. Reynolds (retired), Lois A. Tomlinson,
Patricia L. Moe, and Dorothy H. Hughley, Technical Editing Branch, FDA; and Thomas R. Mulvaney,
Division of Food Chemistry and Technology, FDA.

We acknowledge the following individuals for their valuable comments specific to flexible and semirigid
containers: Pete Adams, International Paper Co.; Kent Garrett, Continental Can Co.; Donald A. Lake,
Roger Genske, and Stan Hotchner, American National Can Co.; Charles Sizer, Tetra Pak International,
Sava Stefanovic, Ex-Cell-O; and Clevel Denny, Jean Anderson, Nina Parkinson, and Jenny Scott,
National Food Processors Association.

Hypertext Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. Chapter 22.
*Author: George W. Arndt, Jr. (NFPA)

Top

B A M | B A M Media | B A M Reagents | Bad Bug Book

Foods Home | FDA Home | Search/Subject Index | Disclaimers & Privacy Policy | Accessibility/Help

Hypertext updated by bap/kwg/cjm 2001-OCT-24

28 of 28 3/28/08 10:27 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 22D
Examination of Containers for Integrity
Glossary and References
Authors

(Return to Table of Contents)

Glossary

BASE PLATE PRESSURE. Force of the base plate that holds the can body and end against the chuck
during the double seaming operation. In general, it has the following effect on the seam formation: low
pressure, short body hook; high pressure, long body hook.

BODY - The principal part of a container, usually the largest part in one piece comprising the sides. The
body may be cylindrical, rectangular, or another shape.

BODY HOOK - The flange of the can body that is turned down in the formation of the double seam.

BOTTOM SEAM - Double seam of the can end put on by the can manufacturer, also known as factory
end seam.

CABLE CUTS - Cuts or grooves worn into can ends and bodies by cables of the runway conveyor
system.

CAN, SANITARY - Full open-top 2-piece drawn can and 3-piece can with double seamed bottom.
Cover or top end is attached with a double seam by the packer after filling. Ends are compound-lined.
Also known as packer's can or open-top can.

CANNER'S END - See packer's end.

CAP TILT - Cap should be essentially level with transfer bead or shoulder.

CHIPPED GLASS FINISH - Defect in which a piece of glass has broken away (chipped) from the
finish surface.

CHUCK - Part of a closing machine that fits inside the end countersink and acts as an anvil to support
the cover and body against the pressure of the seaming rolls.

1 of 7 3/28/08 10:34 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

CHUCK WALL - Part of the can end that comes in contact with the seaming chuck (Fig. 2).

COCKED CAP - Cap not level because cap lug is not properly seated under glass lug.

CODE CUT - Fracture in the metal of a can end caused by improper code embossing.

COLD WELD - Weld appears narrower and lighter than normal and may be scalloped. Fails the pull
test, possibly exhibiting a zipper or sawtooth type of failure.

CONTAMINATION IN WELD AREA - Any visible burn at one or more points along side seam.

COMPOUND - Sealing material consisting of a water or solvent dispersion or solution of rubber and
placed in the curl of the can end. The compound aids in producing a hermetic seal by filling spaces or
voids in the double seam

COUNTERSINK DEPTH - Measurement from top edge of double seam to end panel adjacent to chuck
wall.

COVER - See packer's end.

COVER HOOK - The part of the double seam formed from the curl of the can end. Wrinkling and other
visual defects can be observed by stripping off the cover hook.

CRACKED GLASS FINISH - Actual break in the glass over the sealing surface of the finish. Also
known as split finish.

CRAWLED LAPS - Occurs when two layers of metal are bent and the outer layer looks shorter
because it has a greater radius to traverse than the inner layer, which has a smaller radius, perhaps being
bent almost double. Also known as creep.

CROSS-OVER - The portion of a double seam at the juncture with the side seam of the body.

CROSS-SECTION - A section cut through the double seam for the purpose of evaluating the seam.

CRUSHED LUG - Lug on cap forced over glass lug, causing the cap lug not to seat under glass lug.

CURL - Extreme edge of the cover that is turned inward after the end is formed. In metal can double
seaming, the curl forms the cover hook of the double seam. For the closure for glass containers, the curl
is the rolled portion of metal at the bottom of the closure skirt (may be inward or outward).

CUTOVER - A break in the metal at top of inside portion of double seam caused by a portion of the
cover being forced over the top of the seaming chuck. This condition usually occurs at the cross-over.
Also known as a cut through by some can manufacturers. These manufacturers refer to a cutover as the
same condition without the break.

CUT THROUGH - Gasket damage caused by excessive vertical pressure.

DEADHEAD - An incomplete double seam resulting from the seaming chuck spinning in the end's
countersink during the double seaming operation. Also known as a spinner, skidder, or slip.

DELAMINATION - Any separation of plies (laminate materials) that results in questionable pouch
integrity.

DOUBLE SEAM - Closure formed by interlocking and compressing the curl of the end and the flange
of the can body. It is commonly produced in 2 operations. The first operation roll preforms the metal to

2 of 7 3/28/08 10:34 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

produce the 5 thicknesses or folds; the second presses and flattens them together to produce double
seam tightness.

DROOP - Smooth projection of the double seam outside and below the bottom of the normal seam.
Usually occurs at the side seam lap area.

FACTORY END - See manufacturer's end.

FALSE SEAM - Double seam where a portion of the cover hook and body hook are not interlocked,
i.e., no hooking of body and cover hooks.

FINISH - That part of the glass container for holding the cap or closures.

FLANGE - Outward flared edge of the can body cylinder that becomes the body hook in the double
seaming operation. For weld cans, any flange crack at or immediately adjacent to the weld is a major
defect.

FLEXIBLE CONTAINER - A container, the shape or contour of which, when filled and sealed, is
affected by the enclosed product.

HEAVY LAP - A lap containing excess solder. Also called a thick lap.

HOOK, BODY - See body hook.

HOOK, COVER - See cover hook.

IMPROPER POUCH SEAL - A defect (e.g., entrapped food, grease, moisture, voids, or fold-over
wrinkles) in that area of the closure seal that extends 1/8 inch vertically from edge of seal on food
product side and along full length of seal.

IRREGULAR WELD WIDTH - Any obvious irregularity in weld width along length of side seam.

JUMPED SEAM - See jumpover.

JUMPOVER - Double seam that is not rolled tight enough adjacent to the cross-over; caused by
jumping of the seaming rolls at the lap.

JUNCTURE - The junction of the body side seam and the end double seam, or that point where the 2
seams come together. Also known as the cross-over.

KNOCKED-DOWN FLANGE - Common term for a false seam where the bottom of the flange is
visible below the double seam. A portion of the body flange is bent back against the body without being
engaged with the cover hook.

LAP - The section at the end of the side seam consisting of 2 layers of metal bonded together. As the
term implies, the 2 portions of the side seam are lapped together to allow for the double seam, rather
than hooked, as in the center of the side seam.

LID - See packer's end.

LIP - Projection where the cover hook metal protrudes below the double seam in one or more "V"
shapes. Also known as a vee.

LUG CAP - Closure with raised internal impressions that intermesh with identical threads on the finish
of the glass container. It is a closure with horizontal protrusions that seat under angled threads on the

3 of 7 3/28/08 10:34 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

glass container finish.

MANUFACTURER'S END - End of the can that is attached by the can manufacturer.

NOTCH - Small cut-out section in the lap designed to facilitate the formation or the body hook at
cross-over.

OPEN LAP - A lap that is not properly soldered or has failed by separating or opening because of
various strains in the solder.

OVERLAP - Distance the cover hook laps over the body hook. Any observable loss of overlap along
the side seam is a critical defect.

PACKER'S END - End of the can attached and coded by the food packer. Also known as the canner's
end.

PLATE - General term for tinplate, aluminum, and the steel sheets from which cans are made. It is
usually tin plate, which is black plate with tin applied to it.

PRESSURE RIDGE - Impression (chuck impression) around the inside of the can body directly
opposite the double seam.

PULL-UP - Term applied to distance measured from the leading edge of the closure lug to the vertical
neck ring seam.

SAWTOOTH - Partial separation of the weld side seam overlap at one or more points along the seam. If
observed after performing the pull test, it is considered a critical defect.

SEAM NARROWING - A steadily visible narrowing of the weld at either end of the weld side seam is
a critical defect.

SEAM THICKNESS - Maximum dimension of double seam measured across or perpendicular to

layers of seam.

SEAM WIDTH (LENGTH OR HEIGHT) - Maximum dimension of double seam measured parallel to
folds of seam.

SECURITY - Residual clamping force remaining in the closure application when gasket has properly
seated after processing and cooling.

SEMIRIGID CONTAINER - A container, the shape or contour of which, when filled and sealed, is not
affected by the enclosed product under normal atmospheric temperature and pressure, but which may be
deformed by external mechanical pressure of less than 10 psi (0.7 kg/cm2) (i.e., normal firm finger
pressure).

SIDE SEAM - The seam joining the 2 edges of the body blank to form a can body.

SKIDDER - Can with incompletely finished double seam because the can slipped in the seaming chuck.
In this defect, part of the seam will be incompletely rolled out. The term has the same meaning as
deadhead when referring to seamers that revolve the can. Also known as a spinner.

SOFT CRAB - Colloquial term used to describe a breakdown in the packer's can resulting in a hole
between end and body.

4 of 7 3/28/08 10:34 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

SPINNER - See deadhead and skidder.

STRIPPED CAP - Lug closure applied with too much torque, which causes lugs to pass over glass
lugs. May have vacuum but has no security value.

TIGHTNESS - Degree to which the double seam is compressed by the second operation roll. Tightness
is determined primarily by the degree of freedom from wrinkles in the cover hook. Tightness rating is a
percentage that ranges from 100 to 0, depending on the depth of the wrinkle: 100% indicates no wrinkle
and 0% indicates a wrinkle extending completely down the face of the cover hook. A well-defined
continuous impression around the circumference of the can in the double seam area indicates a tight
seam. This impression is known as a pressure ridge.

TOP SEAM - Top of packer's end seam.

UNEVEN HOOK - Body or cover hook that is not uniform in length.

WELD CRACK - Class I corrosion products plus any observable seam crack, and any cracks that
extend 25% or more across the width of the weld at any point along the weld seam are considered
critical defects.

WELD PROTRUSION - Protrusion of the weld in excess of 1/16 inch beyond the leading or trailing
edge of the can body.

WRINKLE (COVER HOOK) - A waviness occurring in the cover hook from which the degree of
double seam tightness is determined.

ZIPPER - Gross separation of the side seam overlap along all or any part of the side seam. If observed
during pull test, it is a critical defect.

References

1. American Can Company. 1975. Test Procedures Manual (Internal Publication). Barrington Technical
Center, Barrington, IL.

2. American Can Company. 1978. Top Double Seam Inspections and Evaluation: Round Sanitary Style
Steel Cans. Book No. 4800-S. Barrington Technical Center, Barrington, IL.

3. APHA. 1966. Recommended Methods for the Microbiological Examination of Foods, 2nd ed. J.M.
Sharf (ed). American Public Health Association, New York.

4. APHA. 1984. Chapter 55. Canned foods--tests for cause of spoilage. In: Compendium of Methods
for the Microbiological Examination of Foods, 2nd ed. Marvin L. Speck (ed). American Public Health
Association, Washington, DC.

5. Arndt, G.W. 1990. Burst Testing for Paperboard Aseptic Packages with Fusion Seals. Michigan
State University, School of Packaging, East Lansing, MI.

6. ASTM. 1980. Test for leaks using the mass spectrometer leak detector in the inside out mode. E-493.
Annual Book of ASTM Standards. ASTM, Philadelphia.

7. ASTM. 1980. Test for residual gas using the mass spectrometer in the tracer mode. ASTM E-498.
Annual Book of ASTM Standards. ASTM, Philadelphia.

5 of 7 3/28/08 10:34 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

8. ASTM. 1980. Method for testing for residual gas using the mass spectrometer in the detector probe
mode. ASTM E-499. Annual Book of ASTM Standards. ASTM, Philadelphia.

9. ASTM. 1985. Tensile properties of thin plastic sheeting. ASTM D-882 A or B. Annual Book of
ASTM Standards. ASTM, Philadelphia.

10. ASTM. 1992. Method of compression testing for shipping containers D-642-90. Annual Book of
ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging
Products. ASTM, Philadelphia.

11. ASTM. 1992. Method of drop test for filled bags D-959-80-86. Annual Book of ASTM Standards,
Vol. 15.09. Paper; Packaging; Flexible Barrier Materials: Business Copy Products. ASTM,
Philadelphia.

12. ASTM. 1992. Methods for mechanical handling of unitized loads and large shipping cases and
crates D-1083-91. Annual Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier
Materials; Business Imaging Products. ASTM, Philadelphia.

13. ASTM. 1992. Methods for vibration testing of shipping containers D-999-91. Annual Book of
ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging
Products. ASTM, Philadelphia.

14. ASTM. 1992. Practice for conditioning containers, packages, or package components for testing
D-4332-89. Annual Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier
Materials; Business Imaging Products. ASTM, Philadelphia.

15. ASTM. 1992. Standard practice for performance testing of shipping containers and systems
D-4169-91a. Annual Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier
Materials; Business Imaging Products. ASTM, Philadelphia.

16. ASTM. 1992. Terminology of packaging and distribution environments D-996-91. Annual Book of
ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging
Products. ASTM, Philadelphia.

17. ASTM. 1992. Test method for drop test of cylindrical shipping containers D-997-80-86. Annual
Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging
Products. ASTM, Philadelphia.

18. ASTM. 1992. Test method for drop test of loaded boxes D-775-80-86. Annual Book of ASTM
Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging Products.
ASTM, Philadelphia.

19. Bee, G.R., R.A. DeCamp, and C.B. Denny. 1972. Construction and use of a vacuum microleak
detector for metal and glass containers. National Canners Association, Washington, DC.

20. National Food Processors Association. 1989. Flexible Package Integrity Bulletin by the Flexible
Package Integrity Committee of NFPA. Bulletin 41-L. NFPA, Washington, DC.

21. Wagner, J.W., et al. 1981. Unpublished data. Bureau of Medical Devices, Food and Drug
Administration, Washington, DC.

General Reading

Bernard, Dane T. 1984. Evaluating container integrity through biotesting. In: Packaging Alternatives for
Food Processors. Proceedings of National Food Processors Association. NFPA, Washington, DC.

6 of 7 3/28/08 10:34 AM
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

Carnation Company, Can Division. No date. Double seam standards and procedures. Oconomowoc,
WI.

Code of Federal Regulations. 1991. Title 21, part 113. Thermally processed low-acid foods packaged in
hermetically sealed containers. U.S. Government Printing Office, Washington, DC.

Continental Can Company. 1976. Top double seaming manual. New York. (Revisions by H.P.
Milleville, Oregon State University, Corvallis, OR).

Corlett, D.A., Jr. 1976. Canned food-tests for cause of spoilage, pp. 632-673. In: Compendium of
Methods for the Microbiological Examination of Foods. M.L. Speck (ed). American Public Health
Association, Washington, DC.

Food Processors Institute. 1982. Canned Foods, 4th ed. FPI, Washington, DC.

Grace, W.R. & Co., Dewey and Almy. 1971. Evaluating a double seam. Chemical Division, Lexington,
MA.

Lampi, R.A., G.L. Schulz, T. Ciavarini, and P.T. Burke. 1976. Performance and integrity of retort
pouch seals. Food Technol. 30(2):38-46

National Canners Association. 1968. Laboratory Manual for Food Canners and Processors, Vol. 2.
AVI Publishing, Westport, CT.

Put, H.M.C., H. Van Doren, W.R. Warner, and J.T. Kruiswijk. 1972. The mechanisms of
microbiological leaker spoilage of canned foods: A review. J. Appl. Bacteriol. 35:7-27.

Hypertext Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. Chapter 22.
*Authors:Rong C. Lin, Paul H. King, and Melvin R. Johnston

Top

B A M | B A M Media | B A M Reagents | Bad Bug Book

Foods Home | FDA Home | Search/Subject Index | Disclaimers & Privacy Policy | Accessibility/Help

Hypertext updated by bap/kwg/cjm 2001-OCT-24

7 of 7 3/28/08 10:34 AM
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

CHAPTER 10. EXAMINATION OF HEAT PROCESSED, HERMETICALLY SEALED

(CANNED) MEAT AND POULTRY PRODUCTS

George W. Krumm, Charles P. Lattuada,

Ralph W. Johnston, James G. Eye, and John Green

10.1 Introduction

Thermally processed meat and poultry products in hermetically

sealed containers include both shelf stable products as well as
those that must be kept refrigerated (i.e. perishable product).
There are a wide variety of packages designed to totally exclude
air. These include traditional rigid containers, such as metal
cans and glass jars; semi-rigid containers such as plastic cans,
bowls and trays; and flexible containers such as retortable
pouches and bags. The microbiological examination of these food
products requires knowledge and a thorough understanding of food
microbiology, food science, and packaging technology and
engineering. Many books and scientific articles are available on
the processing and the laboratory testing of these products.
Individuals who perform these analyses should be familiar with the
current procedures and methods. Some of these references are
listed in section 10.6.

10.2 Important Terms and Concepts

a. Shelf Stability (commercial sterility):

The term "shelf stability" traditionally has been used

by the Agency and is synonymous with the terms
"commercial sterility" or commercially sterile". Shelf
stability is defined in CFR title 9, part 318, Subpart
G, 318.300 (u) of the Food Safety and Inspection Service
(meat and poultry) USDA regulations. Shelf stability
(commercial sterility) means "the condition achieved by
application of heat, sufficient, alone or in combination
with other ingredients and/or treatments, to render the
product free of microorganisms capable of growing in the
product at non-refrigerated conditions (over 50°°F, 10°°C)
at which the product is intended to be held during
distribution and storage". Such a product may contain
viable thermophilic spores, but no mesophilic spores or
vegetative cells. These products usually are stable for
years unless stored at temperatures of 115-130°°F (46-
55°°C) which may allow swelling or flat sour spoilage to

10-1
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

occur because of germination and growth of the

thermophilic spores. Many low acid canned meat/poultry
products contain low numbers of thermophilic spores.
For this reason, samples of canned foods are not
routinely incubated at 55°°C because the results usually
will be confusing and provide no sound information.
Canned food lots that are to be held in hot vending
machines or are destined for tropical countries are
exceptions to this rule.

b. Hermetically Sealed Container:

A container that is totally sealed to prevent the entry

or escape of air and therefore secure the product
against the entry of microorganisms.

c. Adventitious contamination:

Adventitious contamination may be defined as the

accidental addition of environmental microorganisms to
the contents of a container during analysis. This can
occur if the microbiologist has not sterilized the
puncture site on the container surface or the opening
device adequately, or is careless in manipulating
equipment or cultures. Strict attention to proper
procedures is required to avoid this type of
contamination.

d. Cured Meat/Poultry Products:

Many canned meat/poultry products contain curing salts

such as mixtures of sodium chloride and sodium nitrite.
When included in a canned meat/poultry product
formulation, sodium chloride and sodium nitrite inhibit
the outgrowth of bacterial spores, particularly
clostridial spores. Lowering the pH and increasing the
sodium chloride concentration enhance the inhibitory
action of sodium nitrite. Thus, most canned, cured
meat/poultry products are minimally heat processed and
are rendered shelf stable by the interrelationship of
heat, pH, sodium chloride, sodium nitrite and a low
level of indigenous spores. Spoilage in canned cured
meat/poultry products attributed to underprocessing is
rare. When it occurs, it is usually the result of
improper curing rather than inadequate heating. The
heat processes used for canned, cured, shelf stable
meat/poultry products are unique in that they usually

10-2
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

are not designed to destroy mesophilic bacterial spores

but merely to inhibit their outgrowth.

e. Uncured Meat/Poultry Products:

Canned uncured meat/poultry products are given a much

more severe heat treatment than canned cured products.
The treatment given to canned uncured meat/poultry
products is commonly referred to as a "full retort
cook".

10.21 Classification of Containers

a. Metal and plastic cans with metal double sealed end(s):

Cans must be at room temperature for classification.

Cans are classified as NORMAL if both ends are flat or
slightly concave; FLIPPER when one end of a normal-
appearing can is struck sharply on a flat surface, the
opposite end "flips out" (bulges) but returns to its
original appearance with mild thumb pressure; SPRINGER
if one end is slightly convex and when pressed in will
cause the opposite end to become slightly convex; SOFT
SWELL if both ends are slightly convex but can be
pressed inward with moderate thumb pressure only to
return to the convex state when thumb pressure is
released; HARD SWELL if both ends are convex, rigid and
do not respond to medium hard thumb pressure. A can with
a hard swell will usually "buckle" before it bursts.
Hard swollen cans must be handled carefully because they
can explode. They should be chilled before opening
except when aerobic thermophiles are suspected. Never
flame a can with a hard swell, use only chemical
sanitization.

b. Glass jars:

Classify glass jars by the condition of the lid

(closure) only. Do not strike a glass jar against a
surface as you would a can. Instead shake the jar
abruptly to cause the contents to exert force against
the lid; doing so occasionally reveals a flipper.
Scrutinize the contents through the glass prior to
opening. Compare the contents of the
abnormal/questionable jar with the contents of a normal
jar (e.g., color, turbidity, and presence of gas
bubbles), and record observations.

10-3
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

c. Flexible containers (pouches):

Pouches usually are fabricated from laminates consisting

of two or more layers (plies) of material. Retortable
pouches are the most common type of flexible container
used for canned, shelf-stable products. Most pouches
are 3-ply: an outer ply of polyester film, a middle ply
of aluminum foil, and an inner ply of polypropylene.
The polyester functions as the heat resistant, tough
protective layer; the aluminum foil as a moisture, gas
and light barrier; and the polypropylene functions as
the food contact surface and the film for heat sealing.
The polypropylene also provides added strength, and
protects the aluminum film against corrosion by the food
product. Not all retortable pouches contain an aluminum
foil ply. Pouches and paperboard containers used for
non-retorted, shelf stable products (e.g. pH-controlled
and hot-filled product) or aseptically filled containers
may be quite different from retortable pouches in
construction. Pouches and other flexible containers are
either factory-formed and supplied ready for filling, or
are formed by the processor from roll stock.

10.22 Container Abnormalities

To determine the cause of product abnormalities, both normal and

abnormal containers from the same production lot should be
examined. All observed microbiological results should be
correlated with any existing product abnormalities (Section 10.46
a) such as atypical pH, odor, color, gross appearance, direct
microscopic examination, etc. as well as the container evaluation
findings (Section 10.46, b,c). Non-microbial swells (such as
hydrogen swells) are usually diagnosed by considering all product
attributes because culture results are negative or insignificant.

a. Metal cans, plastic containers and glass jars:

Conditions such as "swells" are defined in Section 10.21

(a). The defects and abnormalities associated with
these containers have been extensively detailed by
others. Rather than include extensive descriptions for
each of them in this section, the analyst is referred to
several excellent references presented in Section 10.6.
These references provide detailed information on the
numerous defects and abnormalities that can occur with
these containers. The analyst should be familiar with
these conditions before beginning any analysis of a

10-4
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

defective or abnormal container. The effect of

processing failures, such as overfilling, closure at low
temperature or high altitude; container damage; and
storage temperature changes, must be taken into
consideration as the analyst evaluates possible causes
for the defect or abnormality. For quick reference, a
Glossary of Terms is provided in Appendices I and II.

b. Pouches:

A Glossary of Terms for these containers can be found in

Appendix III. It is imperative to follow uniform
procedures (Section 10.46,c) when examining defective or
abnormal pouches. The APHA, 1966 reference (Section
10.6) provides detailed information on the analysis of
pouch defects.

10.3 Analysis of Containers

The number of containers available for analysis will vary.

However, it is important that the number be large enough to
provide valid results. Unless the cause of spoilage is clear cut,
at least 12 containers should be examined. With a clear cut
cause, one half this number may be adequate. If abnormal
containers have been reported, but are not available for analysis,
incubation of like-coded containers may reproduce the abnormality.
The "normal" cans should be incubated at 35°°C for 10 days prior to
examination. Incubation temperatures in excess of 35°°C should not
be used unless thermophilic spoilage is suspected. This
incubation may reproduce the abnormality, and thereby document
progressive microbiological changes in the product. Examine the
incubated cans daily. Remove any swells from the incubator as
they develop and culture them along with a normal control. After
the 10 day incubation period, cool the cans to room temperature
and reclassify. Swollen, buckled and blown containers should NOT
be incubated but analyzed immediately along with a normal control.
All steps in the analysis should be conducted in sequence
according to protocol.

10.31 Physical Examination of Metal and Plastic Containers

a. Before opening, visually examine the double end seam(s)

and side seam (if present) for structural defects, flaws
and physical damage; record pertinent observations.

10-5
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

b. Run thumb and forefinger around the inside and outside

of the double seams for evidence of roughness,
unevenness, or sharpness.

c. Using a felt marker, make three slash marks at irregular

intervals across the label and the code-end seam.
Remove the label and copy any label code-numbers to the
side of the container along with a mark indicating the
code end of the can. Correlate any stains on the label
with suspicious areas on the side panel (can body) by
returning the label to its exact position relative to
the slash marks.

d. Examine all non-seam areas of the can and ends for any
evidence of physical damage. If the code is embossed,
carefully examine it for any evidence of puncturing.
Circle any suspect and/or defective areas with an
indelible pen and record this information on the work
sheet. For an illustration of these defects see the
APHA, 1966 reference (Section 10.6).

10.32 Physical Examination of Glass Jars

a. Before opening, remove the label and, using a good light

source such as a microscope light, examine the container
for apparent or suspected defects. Microorganisms may
enter jars through small cracks in the glass. Make note
of any residue observed on the outer surface and the
location.

b. Test the closure gently to determine its tightness.

After sampling has been completed, examine the lid
(closure) and the glass rim (sealing surface) of the
jar. Look for flaws in the sealing ring or compound
inside the closure; for food particles lodged between
the glass and the lid; and for chips or uneven areas in
the glass rim.

10.33 Physical Examination of Pouches

a. Pouches should be examined using an illuminated 5X

magnifier.

b. Hold the pouch in one hand, examine it for

abnormalities, such as swelling, leakage, overfilling,
and defects such as delamination and severe distortion.
Record any pertinent observations.

10-6
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

c. Hold the pouch at both ends and examine both sides for
noticeable cuts, cracks, scratches, food residues,
punctures, missing labels, foreign materials or other
abnormalities.

d. Carefully examine all seal areas for incomplete fusion.

Pay attention to such defects as entrapped product,
wrinkles, moisture and foreign material in the seal.
Particular attention should be given to the final or
closing seal.

e. All actual and suspected defects should be circled with

an indelible marking pen for more detailed examination
after all sampling is complete.

10.4 Analysis of the Contents

Processing errors occur infrequently with canned products, but may

result in the improper processing of large quantities of product.
Swollen cans, for instance, may signal a microbial spoilage
problem. Each abnormality in a "canned" product must be
investigated thoroughly and correctly. The following procedures
should be followed carefully.

10.41 Equipment and Material

a. Incubators 20°°, 35°° & 55 ± 1°°C

b. Vertical laminar flow hood
c. Microscope, microscope slides & cover slips
d. pH meter equipped with a flat electrode
e. Felt-tip indelible marker
f. Illuminated 5X magnifier
g. Sterile Bacti-disc cutter or other suitable opening
device
h. Large, sterile plastic or metal funnel
i. Large autoclavable holding pans
j. Sterile towels
k. Clean laboratory coat and hair covering(s)
l. Sterile wide bore pipettes or 8 mm glass tubing with
cotton plugs
m. Sterile serological pipettes with cotton plugs
n. Safety aspiration device for pipetting (e.g. pro-
pipette)
o. Sterile petri dishes, beakers, and large test tubes
p. Sterile triers, cork borers, scissors, knives and 8"
forceps. Triers can be made from the tail piece of

10-7
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

chrome finish sink drain pipe, 1 1/2" in diameter,

flanged on one end and sharpened on the other end.
q. Sterile cotton swabs with wooden handles in glass test
tubes, one per tube, or commercially sterilized swabs in
paper sleeves
r. Sterile gloves
s. Small wire basket to hold pouches in an upright position
t. Seam analysis tools (micrometer, calipers, saw,
countersink meter, metal plate scissors, nippers).
u. Vacuum gauge
v. Light source such as a microscope light
w. Sonic cleaning apparatus
x. Transparent acrylic plate with a hole and tubing to a
vacuum source
y. Bituminous compound in strips (tar type strips usually
available in hardware stores) stored in the 35°°C
incubator
z. Seamtest Type U (Concentrate), Winston Products Co., Inc
Box 3332, Charlotte, N.C., Dilute 1:300 with distilled
water for use.
aa. Wooden dowels, 1/2" diameter
bb. Gas cylinder clamp
cc. Abrasive chlorinated cleaner or a scouring pad

10.42 Media and Reagents

a. Modified Cooked Meat Medium (MCMM) STEAM JUST BEFORE USE

b. Brom Cresol Purple Broth (BCPB) or Dextrose Tryptone
Broth
c. Plate Count Agar
d. APT Agar
e. KF Broth
f. Strong's Sporulation Medium
g. Gram stain reagents
h. Spore stain
i. Dishwashing detergent
j. Chlorine solution, (Commercial Bleach with approximately
5% available chlorine diluted 1:100 with 0.5 M phosphate
buffer, pH 6.2)

10.43 Preparation

a. The Analyst

i. The analyst must wear a clean full length

laboratory coat.

10-8
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

ii. Hair must be completely covered with a clean,

disposable operating room type hair cover. A
surgical face mask should be worn; if the analyst
has facial hair such as beards and sideburns, the
mask must completely cover it.

iii. Hands, forearms and face should be washed with

germicidal soap and water.

iv. The analyst should wear safety glasses or goggles,

preferably in combination with some type of face
shield when opening swollen cans or cans suspected
of being contaminated with Clostridium spp.

b. Preparing the Environment

i. If possible, the analysis should be done in a

vertical laminar flow hood. If a hood is not
available, the area used must be clean and
draft-free.

ii. Flat cans should be opened in the laminar flow

hood.

iii. Swells may explode or spew, therefore they should

be opened outside the hood and the container
transferred to the hood only after it is opened and
all gas released.

iv. Disinfect the work surface before beginning any

work.

c. Preparing Metal Cans Prior to Opening

i. Scrub the non-coded end of the metal can with

abrasive cleaner or a scouring pad. This removes
bacteria-laden oil and protein residues. Rinse
well with tap water. Cans with an "easy open" end
usually are coded on the bottom. Record the code
exactly and prepare the code end as described
above.

ii. Sanitize the cleaned end with chlorine solution

(Section 10.42 j) either by placing clean tissues
over the end and saturating it with chlorine
solution or by immersing the end in a shallow pan
containing the solution. Allow a 15-minute contact

10-9
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

time; wipe dry with sterile towels or tissue. (An

alternative sanitization procedure which can be
used on Normal-appearing cans ONLY is to heat the
entire can surface using a laboratory burner or a
propane torch until the metal becomes slightly
discolored from the heat.) Proceed as outlined in
Section 10.44.

d. Preparing Jars Prior to Opening

i. Scrub the surface of the jar closure with abrasive

cleaner or scouring pads. Rinse well with tap
water.

ii. Sanitize the jar closure with chlorine (Section

10.42 j) either by placing clean tissues over the
closure and saturating it with chlorine solution or
immersing the closure in a shallow pan containing
the solution. Allow a 15-minute contact time; wipe
dry with sterile towels or tissue.

e. Preparing Plastic Containers Prior to Opening

i. Scrub the bottom surface of the container with

abrasive cleaner or scouring pads. Rinse well with
tap water.

ii. Sanitize the bottom with chlorine solution (Section

10.42 j) by placing clean tissues over the bottom
and saturating it with chlorine or immersing the
bottom of the container in a shallow pan containing
the solution. Allow a 15-minute contact time; then
wipe dry with sterile towels or tissue.

f. Preparing Normal and Abnormal-Appearing Flexible

Retortable Pouches Prior to Opening

i. Clean the outside of the pouch with a sanitizer and

rinse well.

ii. Sanitize the entire pouch in a suitably sized pan

with chlorine solution (Section 10.42 j). Allow a
15-minute contact time; then wipe dry with sterile
towels or tissue.

10-10
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

g. Preparing Swollen Cans Prior to Opening

i. Scrub the non-coded end of the chilled metal can

with an abrasive cleaner or a scouring pad. This
removes bacteria-laden oil and protein residues.
Rinse well with tap water.

ii. Sanitize the cleaned end with chlorine solution

(Section 10.42 j) either by placing clean tissues
over the end and saturating it with chlorine
solution or immersing the end in a shallow pan
containing the solution. Allow a 15-minute contact
time; then wipe dry with sterile towels or tissue.

h. Opening Devices

i. The preferred type of opening device is the

adjustable Bacti-disc cutter (available from the
Wilkens-Anderson Company, 4525 W. Division Street,
Chicago, IL.; a similar device is available from
the American National Can Co., 1301 Dugdale Rd.,
Waukegan, IL. Order Number WT2437). The opener
should be pre-sterilized or heated in a flame to
redness. If this type of device is not available,
individually packaged and heat sterilized regular,
all metal, kitchen-type can openers may be used.
The advantage of the Bacti-disc type opener is that
it causes no damage to the double seam (simplifying
later examination) and the size of the opening can
be adjusted.

ii. Sometimes a large can (e.g. a #10 size can) may be

difficult to open. The analyst could be exposed to
pathogens or their toxins if the can is not
properly secured. The container can be held
tightly with a gas cylinder clamp secured in an
inverted position in a shallow metal drawer or tray
lined with a large disposable poly bag or an
autoclavable tray to contain any overflow. Place
the #10 container against the clamp and secure the
strap. Rotate the can and continue cutting until
the opening is completed. The metal tray and liner
may be removed for cleaning and the clamp is
autoclavable.

10-11
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10.44 Sampling

a. Normal-Appearing Metal Cans and Jars with Metal Closures

i. Prepare the area and can or jar closure as

described in section 10.43.

ii. Shake the container to distribute the contents.

iii. Use a sterilized opening device to cut the desired

size entry hole. Transfer samples immediately to
the selected media with a sterile pipette or swab
and proceed as outlined in Section 10.45.

iv. Aseptically transfer a representative amount of the

product to a sterile test tube or other sterile
container as a working reserve. Use a pipet or
sterile spoon to accomplish this.

v. Caution: The contents from overfilled cans may

flow out of the hole onto the surrounding lid
surface at the time of opening. This material can
then drain back into the can when the opening
device is removed. Should this occur, terminate
the analysis.

b. Normal and Abnormal-Appearing Plastic Containers

i. Immediately after removing the container from the

chlorine solution and wiping the excess liquid, use
a very hot, sterilized opening device to cut the
desired size entry hole. Transfer samples
immediately to the selected media with a sterile
pipette or swab and proceed as outlined in Section
10.45.

ii. Aseptically transfer a representative amount of the

product to a sterile test tube or other sterile
container as a working reserve. Use a pipet or
sterile spoon to accomplish this.

c. Normal and Abnormal Appearing Flexible Retortable

Pouches

i. Place the disinfected pouch upright in a sterile

beaker and cut a two inch strip about one quarter

10-12
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

of an inch under the seam edge using a sterile

scissors. If possible, use a pipette to remove
some of the pouch contents, otherwise use a swab.
Transfer the samples immediately to the selected
media with a sterile pipet or swab, proceed as in
section 10.45.

ii. Aseptically transfer a representative amount of the

product to a sterile test tube or other sterile
container as a working reserve. Fold the edge of
the opened pouch over against itself several times
and secure with tape until the microbiological
analysis is complete.

d. Swollen Cans

i. Cans displaying a hard swell should be chilled

before opening. Most foods spoiled by Bacillus
stearothermophilus will not produce gas (flat sour
spoilage). However, if nitrate or nitrite is
present in the meat/poultry product, gas may be
produced by this microorganism. Cold usually will
kill B. stearothermophilus resulting in no growth
in Bromcresol Purple Broth. If possible, save one
or two cans and store without refrigeration.

ii. NEVER FLAME A SWOLLEN CONTAINER - IT MAY BURST.

Place the container to be opened in a large,
shallow, autoclavable pan. The side seam, if
present, should be facing away from the analyst. A
container with a hard swell may forcefully spray
out some its contents, posing a possible hazard to
the analyst if the contents are toxic. Therefore,
these cans should be considered a biohazard and
precautions must be taken to protect the analyst.
Protective gloves should be worn and the lab coat
should be tucked inside the cuffs of the gloves or
at least secured around the wrist. Some type of
facial shield is also recommended.

iii. Place the sanitized container into a biohazard bag

and cover with a sterile towel or invert a sterile
funnel with a cotton filter in the stem over the
can. Place the point of the sterile opening device
in the middle of the container closure. Make a
small hole in the center of the sterilized
end/closure. Try to maintain pressure over the

10-13
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

hole. Release the instrument slowly to allow gas

to escape into the towel or funnel.

iv. After the gas pressure has been released, enlarge

the opening to the desired size to permit sampling
and aseptically remove some of the container
contents. Sample as outlined in (a) above.

10.45 Culturing

a. Inoculation of Culture Media

i. The sampling and transfer processes must be

conducted aseptically; care must be taken to
prevent contamination during the various
manipulations.

ii. Transfer the sample at once to the selected media,

inoculating each tube at the bottom. Whenever
possible, use a pipet and pro-pipette to remove 1-2
ml of product for inoculating each tube of medium.
When the nature of the meat/poultry product makes
it impossible to use a pipet, use a sampling swab
(holding it by the very end of the shaft) to
transfer 1-2 g of the product to each tube. This
is accomplished by plunging the swab into the
product, then inserting the swab as far as possible
into the appropriate tube of medium and breaking
off the portion of the shaft that was handled. Use
one swab for each tube of medium. When inoculating
MCMM, force the broken swab to the bottom of the
tube by using the tip of another sterile swab.

iii. For each sample, inoculate 2 tubes of MCMM which

were steamed (or boiled) for 10 minutes and cooled
just before use and 2 tubes of Bromcresol Purple
Broth. If a tube of KF medium is inoculated at the
same time, the presence of enterococci can be
determined rapidly.

iv. As a process control, place uninoculated swabs into

each of two tubes of MCMM and BCP and one swab into
KF broth (if used). Additionally, label two
uninoculated tubes of each medium to serve as
controls. If multiple samples are cultured at the
same time, only one set of control tubes are needed
for each medium and each temperature.

10-14
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

v. After all tubes have been inoculated with a sample,

aseptically transfer approximately 30 ml or a 30 g
portion of the container contents to a sterile
tube, Whirl-Pak® or jar for retention as a working
reserve sample. Appropriately label the container
and store it in a refrigerator at approximately
4°°C.

vi. Finally, transfer a portion of the container

contents to a sterile Petri plate, clean jar or
beaker for pH, microscopic, organoleptic and other
relevant analyses (10.46).

vii. Cover the hole made in the container with several

layers of sterile aluminum foil, secure the foil
with tape and then store the container in a
refrigerator at approximately 4°°C. This serves as
the primary reserve. Re-enter it only as a last
resort. If the sample is a regulatory sample,
chain of custody records must be maintained on it.

b. Incubation of Culture Media

i. Incubate one tube each of MCMM and BCP at 35°°C and

one tube each at 55°°C. If used, incubate the tube
of KF medium at 35°°C. For the MCMM and BCP
controls, incubate one tube at 35°° and one at 55°°C.

ii. Observe all tubes at 24 and 48 h. Tubes incubated

at 35°°C that show no growth should be incubated for
5 days before discarding. Tubes incubated at 55°°C
should be incubated for 3 days before discarding.
Subculture any questionable tubes, especially if
the product under examination contributes
turbidity.

c. Identification of Organisms

i. Use conventional bacteriological procedures to

characterize the type(s) of microbial flora found
in the contents of the container.

10-15
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

ii. Use descriptive terms such as: mixed culture or

pure culture, anaerobic or aerobic growth, spore
former or non-sporeformer, mesophile or
thermophile, cocci or rods.

iii. Cultures should be examined using a Gram stain.

Gram stains should be done only on 18-24 h
cultures. Record the morphological types observed
and their Gram reaction. If the container contents
are examined microscopically using a methylene blue
stain, record those observations as well. If
endospores are present, the spore stain can be used
for better definition of spore type and placement.

iv. Record all biochemical test results in addition to

any characteristic growth patterns on differential
and/or selective media.

v. MCMM tubes showing a bright yellow color with

visible gas bubbles, and containing gram positive
or gram variable rods should be suspected of
containing gas-forming anaerobes. If Clostridium
botulinum is suspected, sub-cultures should be made
and incubated for 4-5 days. The original tube
should be reincubated to check for spores. After 4
- 5 days incubation, test the cultures for toxin by
the mouse bioassay (see Chapter 14).

10.46 Supportive Determinations

a. Examination of Container Contents

i. Determine the pH of the sample (10.45, a, vii)

using a flat electrode. Disinfect the electrode
after taking this measurement.

ii. If applicable, determine the water activity of the

sample (Section 2.4).

iii. Examine the sample microscopically by making a

simple methylene blue or crystal violet stain. A
Gram stain is of no value since the age of the
cells is not known and Gram-stain reactions may not
be dependable in the case of old cells. Prepare a
spore stain if the contents of a swollen container
show signs of digestion and few bacterial cells.

10-16
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

iv. Note abnormalities observed in the container

contents such as off-odors, off-color, changes in
consistency and texture when compared with normal
product. DO NOT TASTE!

b. Examination of Metal and Plastic Cans

NOTE: Whenever possible a "normal" companion can should

be examined along with the abnormal one.

i. After a reserve sample has been taken and all

examinations are complete, discard any remaining
product into an autoclavable bag and terminally
sterilize.

ii. Disinfect the inside of the container with a

phenolic disinfectant and carefully clean it with a
stiff brush or use an ultra sonic bath. Do not
autoclave the container since this may destroy any
defects.

iii. Examine the interior lining of metal containers for

blackening, detinning and pitting.

iv. The container code should have been recorded prior

to analysis; if it was not, do so now. Sometimes
embossed codes are poorly impressed and can be
revealed by rubbing a pencil on a paper held over
the code. If this does not work, place a thin
smooth piece of paper over the code, hold securely
and rub the paper with a clean finger in order to
impress the paper. Rerub the paper with a finger
coated with graphite. This is superior to using a
pencil to rub the code. If that fails, rub the
code with carbon paper. Place transparent adhesive
tape over the code and rub the tape with the back
of a fingernail. Lift the tape and transfer it to
any document requiring the can code. The latter
two techniques allow a record to be kept of any
partial numbers or symbols. It is also possible to
wait until the can is emptied, then view the
reverse of the code from the inside. If needed,
the code can be viewed in a mirror.

v. When leakage from double seams or side seams is

suspected, remove excess metal from the opened end,
leaving a 0.5 - 1 cm flange. Dry thoroughly,

10-17
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

preferably overnight, in the 55°°C incubator. Add

leak detection liquid (10.41z) to the can to a
depth of 2-4 cm. Place a microleak detector on the
open end of the container. The leak detector
consists of a transparent acrylic plate with a
vacuum gauge and connector for a vacuum source.
Place a gasket (cut pieces of an automobile tire
inner tube will do) between the apparatus and the
can. If the fit is not tight (e.g., end seam is
bent), use modeling clay to fill in the gaps.
Large cans without beading or thin metal cans
having a wider diameter than height may collapse
when vacuum is applied. To prevent this from
happening, use 1/2" wooden dowels cut to the
appropriate length to support the can sides.
Bituminous compound on the dowel ends will hold
them in place. Generally, 4 dowels are sufficient
for a #10 can. Apply the gasket and any bituminous
compound, to the open can end and fit the leak
detector plate in place. Connect the vacuum and
apply 10 inches vacuum to the can. Swirl the
liquid to dissipate bubbles formed by gases
dissolved in the liquid. Examine seams by covering
them with the diluted Seamtest. Leaks are
identified by a steady stream of bubbles or a
steadily increasing bubble size. After carefully
examining all seams for leaks, increase the vacuum
to 20 inches vacuum and re-examine the seams.
Leave the can under vacuum until a leak appears or
for a maximum of 2 h, and examine at half-hour
intervals. Mark the location of leaks on the can's
exterior using a marking pen. When reporting, note
which seam, and the distance from the side seam or
some other appropriate reference point. If no
leaks were found, note test conditions (time and
amount of vacuum drawn).

vi. Perform a tear-down examination of the double

seams. The following references in Section 10.6
will guide you through this process: APHA, 1966;
Food Processors Institute, 1988; Double Seam
Manual; Evaluating a Double Seam, FDA
Bacteriological Analytical Manual, 1992.

vii. The tightness of double seams formed by plastic

cans and metal can ends may be evaluated by
comparing the actual seam thickness to the

10-18
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

calculated thickness of the plastic flange, neck,

or metal end. This would include three thicknesses
of plastic and two of metal. Also, assess
tightness by inspecting the pressure ridge, since
it reflects the compression of the plastic body
wall. The pressure ridge should be visible and
continuous. Each packer may have different
specifications for the finished seams; if
necessary, the analyst must call the in-plant
inspector and ask for specifications for the
container of interest.

c. Examination of Pouches

i. The best way to determine if a pouch has leaked is

by the type of microorganisms recovered.

ii. The pouch should be examined microscopically

looking for points of light coming through the
film. These are potential leakage sites.

10.47 Interpretation of Results

Use Tables 2, 3 and 4 to arrive at possible causes of spoilage

based on all laboratory results. Caution: The tables are based
on a single cause of spoilage. If there are multiple causes, the
tables may not help.

10.5 Examination of Canned, Perishable Meat/Poultry Products

Perishable meat and poultry products, such as hams, luncheon

meats, and loaves are packaged in hermetically-sealed containers
and then heat-processed to internal temperatures of not less than
150°°F (65.5oC) and usually not greater than 160°°F (71oC).
"Perishable, Keep Refrigerated" must appear on the label of these
products. Although they are not shelf stable, good commercial
processing usually will destroy vegetative bacterial cells. The
combined effects of sodium nitrite, salt, refrigeration, and low
oxygen tension retard the outgrowth of the few vegetative cells
and/or spores that may survive the process. Such products can
retain their acceptable quality for 1 to 3 years when properly
processed and refrigerated.

10.51 Analysis of Containers

See Sections 10.3 - 10.33

10-19
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10.52 Analysis of the Contents

a. Equipment and Material

See Section 10.41

b. Media and Reagents

See Section 10.42

c. Preparation

See Section 10.43

d. Sampling

i. Using procedures already described (Section 10.44)

remove approximately 50 g of sample with a
sterilized trier, large cork borers, scissors,
knife or forceps.

ii. Place the sample into a sterile blender jar or

Stomacher bag, add 450 ml of sterile Butterfield's
Phosphate Diluent and homogenize for 2 minutes.
This is a 1:10 dilution; make additional dilutions
through at least 10-4. Proceed with the culturing
steps given in Section 10.52 (e, f & g).

iii. After sampling, cover the container opening with

sterile aluminum foil several layers thick and
secure with tape. Place the opened sample unit in
the freezer until the analysis is complete.

e. Aerobic Plate Counts

i. Pipet 1 ml of each dilution prepared in 10.52 (d)

into each of two sets of duplicate pour plates
according to the instructions given in Section 3.4.

ii. Prepare one dilution set with Plate Count Agar.

Incubate this set at 35°°C for 48 h.

iii. Substitute APT agar for the Plate Count Agar in the
other set of plates. Incubate this set at 20°°C for
96 h.

10-20
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

iv. Count and record the results from both sets as

described in Section 3.4.

f. Gas-Forming Anaerobes (GFAs)

i. Steam tubes of MCMM for 10 minutes and cool just

prior to use.

ii. Inoculate each tube with l ml of each dilution

prepared in 10.52 (d). Begin with the 1:10
dilution and continue with subsequent dilutions.
Use a separate pipet for each dilution. Dilutions
must be sufficiently high to yield a negative
endpoint. Be sure that the inoculum is deposited
near the bottom of the tube.

iii. Incubate these tubes for 48 h at 35°°C, but read

daily.

iv. Consider any MCMM tubes showing a bright yellow

color, containing visible gas bubbles, and
containing gram positive or gram variable rods as
positive for GFAs.

v. Based upon the highest dilution showing these

organisms, report the approximate number of
gas-forming anaerobes per gram, calculated as the
reciprocal of the highest positive dilution. If
skips occur, disregard the final actual dilution
and calculate the end point at the dilution where
the skip occurred. This is only an approximation
of the gas forming anaerobe count. A minimum of
three tubes per dilution and an MPN table must be
used for a more accurate determination.

vi. If Clostridium botulinum is suspected,

representative tubes that have not been opened
should be reincubated for a total of 4 - 5 days and
then tested for botulinum toxin using the mouse
bioassay (Chapter 14).

g. Enterococci

i. Transfer 1 ml of each dilution prepared in 10.52(d)

to individual tubes of KF broth. Use a separate
pipette for each dilution. Begin with the 1:10
dilution and continue with each subsequent

10-21
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

dilution. Dilutions must be sufficiently high to

yield a negative end point.

ii. Incubate these tubes at 35°C for 48 h. Tubes

showing a yellow color, turbidity and buttoning of
growth are presumptive positives.

iii. Confirm all presumptive positives microscopically.

Either wet mounts examined under low light or gram
stained preparations are suitable for these
microscopic determinations. Microscopic
determinations yielding cells with ovoid
streptococcal morphology shall be considered
confirmed positive.

iv. Report the approximate number of enterococci per

gram, calculated as the reciprocal of the highest
positive confirmed dilution. If skips occur,
disregard the final actual dilution and calculate
the end point at the dilution where the skip
occurred. This is only an approximation of the
number of enterococci. A minimum of three tubes
per dilution and an MPN table must be used for a
more accurate determination of organisms as
described in 10.43-10.45 and Tables 2, 3 and 4.

10-22
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10.6 Selected References

APHA 1966. Recommended Methods for the Microbiological

Examination of Foods. 2nd Edition. American Public Health
Association, Inc., New York, New York.

Bee, G. R. and Denny, C. B., 1972, First Revision.

Construction and Use of a Vacuum Micro-Leak Detector for
Metal and Glass Containers. National Canners Association,
(now NFPA), Washington, D.C.

Crown Cork & Seal. Top Double Seaming Manual. Crown Cork
and Seal Co., Inc., 9300 Ashton Road, Philadelphia, PA 19136

Cunniff, P. (ed.). 1995. Official Methods of Analysis of

AOAC International, 16th Edition. Sections 17.6 - 17.8. AOAC
International, Inc., Gaithersburg, MD 20877.

Denny, C., Collaborative Study of a Method for the

Determination of Commercial Sterility of Low-Acid Canned
Foods, Journal of the Association of Official Analytical
Chemists 55 (3):613 (1972).

Double Seam Manual. Carnaud Metalbox Engineering, 79

Rockland Road, Norwalk, Connecticut 06854

Evaluating a Double Seam. W. R. Grace and Company, Grace

Container Products, 55 Hayden Ave., Cambridge, Massachusetts
02173

Food and Drug Administration, Bacteriological Analytical

Manual, Division of Microbiology, Center for Food Safety and
Applied Nutrition, 7th ed., 1992. Association of Official
Analytical Chemists, 1111 North 19th Street, Suite 210,
Arlington, VA 22209.

Food Processors Institute 1988. Canned Foods: Principles of

Thermal Process Control, Acidification and Container Closure
Evaluation. The Food Processors Institute, Washington, D.C.
20005.

Hersom, A. C. and Hulland, E. D., 1964. Canned Foods, An

Introduction to Their Microbiology. Chemical Publishing
Company, Inc. New York, New York.

10-23
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

National Food Processors Association, 1979. Guidelines for

Evaluation and Disposition of Damaged Canned Food Containers
Bulletin 38-L, 2nd Edition. National Food Processors Assoc.,
Washinton, D.C.

National Food Processors Association, 1989. Flexible Package

Integrity Bulletin by the Flexible Package Integrity
Committee of NFPA. Bulletin 41-L. NFPA, Washington, D.C.

Schmitt, H. P. 1966. Commercial Sterility in Canned Foods,

Its Meaning and Determination. Assoc. Food and Drug
Officials of the U.S. 30:141.

Townsend, C. T., 1964. The Safe Processing of Canned Foods.

Assoc. Food and Drug Officials of the U.S. 28:206.

Townsend, C. T., 1966. Spoilage in Canned Foods. J. Milk

Food Tech. 20 (1):91-94.

United States Department of Agriculture, Food Safety

Inspection Service. Code of Federal Regulations, Title 9,
part 318.300, Subpart G (u).

Vanderzant, C., and D. F. Splittstoesser (ed.). 1992.

Compendium of Methods for the Microbiological Examination of
Foods, 3rd Edition. Amer. Publ. Hlth. Assoc., Washington,
D.C. 20005.

10-24
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix I

Glossary of Metal/Plastic Can Seam Terminology

for Container Components and Defects

The same terms that are used to describe an all-metal seam apply
equally well to the metal end/plastic body seam.

Base Plate: Part of a closing machine which supports cans

during seaming operation.

Beaded Can: A can which is re-enforced by having ring

indentations around the body. The bead tends to keep the can
cylindrical and helps to eliminate paneling of the can body.

Body: Principal part of a container - usually the largest

part in one piece containing the sides (thus sidewall or body
wall).

Body Hook: Can body portion of double seam. Prior to

seaming, this portion was the flange of the can.

Bottom Seam: Factory end seam. The double seam of the can
end put on by the can manufacturer.

Buckling: A distortion in a can end.

Can Size: Two systems are commonly used to denote can size:

i. An Arbitrary system (1, 2, etc.) with no relation

to finished dimension.

ii. A system indicating the nominal finished dimensions

of a can; e.g. "307 x 512." In this example, the
first group of digits ("307") refers to the can's
diameter and the second set ("512"), the can's
height. The first digit in each set represents
inches, and the next two digits represent
sixteenths of an inch. Hence, the example can has
a diameter of 3-7/16 and a height of 5-12/16 (or 5-
3/4) inches.

Chuck: Part of a closing machine which fits inside the

countersink and in the chuck wall of the end during seaming.

10-25
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Closing Machine: Also known as a double seamer. Machine

which double seams the lid onto the can bodies.

Compound: Rubber or other material applied inside the end

curl to aid in forming a hermetic seal when the end is double
seamed on the can body.

Contamination in Weld Area: Any visible burn at one or more

points along the side seam of a welded can. This is a major
defect.

Countersink: On a seamed end, the perpendicular distance

from the outermost end panel to the top seam.

Cover: Can end placed on can by packer. Also known as top,

lid, packer's end, canner's end.

Cover Hook: That part of double seam formed from the curl of
the can end.

Cross Over: The portion of a double seam at the lap.

Cross Section: Referring to a double seam, a section through

the double seam.

Curl: The semi-circular edge of a finished end prior to

double seaming. The curl forms the cover hook of the double
seam.

Cut Code: A break in the metal of a can due to improper

embossing-marker equipment.

Cut-Over: During certain abnormal double seaming conditions,

the seaming panel becomes flattened and metal is forced over
the seaming chuck forming a sharp lip at the chuck wall. In
extreme cases the metal may split in a cut-over.

Dead-Head: An incompletely rolled finished seam. Also known

as a skip, skid or spinner.

Double Seam: The joint between the end and the can body
formed by rolling the curl under the flange (1st operation)
and then pressing the metal together (2nd operation).

Droop: A smooth projection of double seam below the bottom of

a normal seam. While droops may occur at any point of the
seam, they usually are evident at the side seam lap. A

10-26
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

slight droop at the lap may be considered normal because of

additional plate thickness incorporated into the seam
structure.

Excessive Slivers: One or more slivers which are 1/32" or

longer. This is a minor defect of welded cans.

Factory End: Bottom or can manufacturer's end.

False Seam: A seam fault where the end and body hook are not
over-lapped (engaged), although they give the appearance of a
properly formed seam. Also see Knockdown Flange.

Feather: Beginnings of a cut-over. See Sharp Edge.

First Operation: The first operation in double seaming. In

this operation, the curl of the end is tucked under the
flange of the can body which is bent down to form cover and
body hook, respectively.

Flange: The flared portion of the can body which facilitates

double seaming.

Flange Crack: Any crack at the flange or immediately adjacent

to the weld of welded cans. This is a major defect.

Headspace: The free space above the contents of a can and the
can lid.

Heavy Lap: A lap containing excess solder. Also called a

thick lap.

Hook: (i). The bent over edges of a body blank, which form
the side seam lock (ii). The body and cover hooks in a
double seam.

Internal Enamel: A coating applied to the inside of the can

to protect the can from chemical action by the contents or to
prevent discoloration. A lacquer is usually clear; an enamel
is pigmented and opaque.

Jumped Seam: A double seam which is not rolled tight enough

adjacent to the crossover caused by jumping of the seaming
rolls at the lap.

Knockdown Flange: A seam defect in which the flange is bent

against the body of the can. The cover hook is not tucked

10-27
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

inside the body hook, but lies outside of it. False seams,
knockdown flanges and soft crabs are degrees of the same
effect. In order to distinguish the degree of the defect,
the following terminology is suggested:

False Seam: The cover hook and body hook are not tucked
for a distance of less than an inch. Thus it may not be
possible to detect a false seam until the can is torn
down.

Knockdown Flange: As above, but more than an inch in

length. Body hook and cover hook in contact, but not
tucked.

Soft Crab: A defect in which the body of the can is

broken down and does not contact the double seam. Thus,
there is a wide open hole in the can below the double
seam where the body was not incorporated into the seam.

Lap: The soldered but not locked portions of a side seam at

the ends of the can body before seaming and removing the can
from the chuck at completion of the operation.

Lid: See Cover.

Lip, Spurs or Vees: Irregularities in the double seam due to

insufficient or sometimes absent overlap of the cover hook
with the body hook, usually in small areas of the seam. The
cover hook metal protrudes below the seam at the bottom of
the cover hook in one or more "V" shapes.

Loss of Overlap: Any observable loss of overlap along the

side seam of a welded can. This is a critical defect.

Loose Tin: A metal can which does not appear swollen, but
slight pressure reveals a looseness.

Mislock: A poor or partial side seam lock, due to improper

forming of the side seam hooks.

Neck: The thickness of the top of the sidewall (body wall) of

a plastic tub, one tenth of an inch below the junction of the
flange and the sidewall.

Notch: A small cut-away portion at the corners of the body

blank. This reduces droop when double seaming.

10-28
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Oozier: An imperfect can which allows the escape of the

contents through the seam.

Open Lap: A lap failed due to various strains set up during

manufacturing operations. Also caused by improper cooling of
the solder (See Weak Lap). A lap which is not properly
soldered so the two halves are not properly joined.

Over Lap: The distance the cover hook laps over the body
hook.

Paneling: A flattening of the can side. Also used to define

concentric (expansion) rings in can ends.

Peaking: Permanent deformation of the expansion rings on the

can ends due to rapid reduction of steam pressure at the
conclusion of processing. Such cans have no positive
internal pressure and the ends can be forced back more or
less to their normal position.

Perforation: Holes in the metal of a can resulting from the

action of acid in food on metal. Perforation may come from
inside due to product in the can or from outside due to
material spilled on the cans.

Pleat: A fold in the cover hook which extends from the edge
downward toward the bottom of the cover hook and sometimes
results in a sharp droop, vee or spur.

Pressure Ridge: A ridge formed on the inside of the can body

directly opposite the double seam, as a result of the
pressure applied by the seaming rolls during seam formation.

Pucker: A condition which is intermediate between a wrinkle

and a pleat in which the cover hook is locally distorted
downward without actual folding. Puckers may be graded the
same way as wrinkles.

Sanitary Can: Can with one end attached, the other end put on
by the packer after the can is filled. Also known as
packer's can or open top can.

Sawtooth: Partial separation of the side seam overlap at one

or more points along the side seam after performing the pull
test on a welded side seam. This is a critical defect.

10-29
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Seam Arrowing: A readily visible narrowing of the weld at

either end of the can body. This is a major defect.

Seam Width: The maximum dimensions of a seam measured

parallel to folds of the seam. Also referred to as the seam
length or height.

Seam Thickness: The maximum dimension measured across or

perpendicular to the layers of the seam.

Second Operation: The finishing operation in double seaming.

The hooks formed in the first operation are rolled tight
against each other in the second operation.

Sharp Edge: A sharp edge at the top of the inside portion of

the double seam due to the end metal being forced over the
seaming chuck.

Side Seam: The seam joining the two edges of a blank to form
a body.

Skipper / Spinner: See Deadhead.

Uneven Hook: A body or cover hook which is not uniform in

length.

Vee: See Lip.

Weak Lap: The lap is soldered and both parts are together.
However, strain on this lap (e.g. by twisting with the
fingers) will cause the solderbond to break.

Weld Crack: Any observable crack in a welded side seam. This

is a critical defect.

Worm Holes: Voids in solder usually at the end of the side

seam. May extend completely through the width of the side
seam.

Wrinkle: The small ripples in the cover hook of a can. A

measure of tightness of a seam.

10-30
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix II

Glossary of Glass Container Parts

From a manufacturing standpoint, there are three basic parts to a

glass container based on the three parts of glass container molds
in which they are made. These are the finish, the body and the
bottom.

Finish: The finish is that part of the jar that holds the cap
or closure. It is the glass surrounding the opening in the
container. In the manufacturing process, it is made in the
neck ring or the finish ring. It is so named since, in early
hand glass manufacturing, it was the last part of the glass
container to be fabricated, hence "the finish". The finish
of glass containers has several specific areas as follows:

Continuous Thread: A continuous spiral projecting glass ridge

on the finish of a container intended to mesh with the thread
of a screw-type closure.

Glass lug: One of several horizontal tapering protruding

ridges of glass around the periphery of the finish that
permit specially designed edges or lugs on the closure to
slide between these protrusions and fasten the number of
lugs on the closure and their precise configuration is
established by the closure manufacture.

Neck Ring Parting Line: A horizontal mark on the glass

surface at the bottom of the neck ring or finish ring
resulting from the matching of the neck ring parts with the
body mold parts.

Sealing Surface: That portion of the finish which makes

contact with the sealing gasket or liner. The sealing
surface may be on the top of the finish, or may be a
combination of both top and side seal.

Vertical Neck Ring Seam: A mark on the glass finish resulting

from the joint of matching the two parts of the neck ring.
NOTE: Some finishes are made in a one-piece ring and do not
have this seam.

Body: The body of the container is that portion which is made

in the "body-mold" in manufacturing. It is the largest part
of the container and lies between the finish and the bottom.

10-31
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

The characteristic parts of the body of a glass container

are:

Heel: The heel is the curved portion between the bottom and
the beginning of the straight side wall.

Mold Seam: A vertical mark on the glass surface in the body

area resulting from matching the two parts of the body mold.

Shoulder: That portion of a glass container in which the

maximum cross-section or body area decreases to join the neck
or finish area. Most glass containers for processed foods
have very little neck. The neck would be a straight area
between the shoulder and the bottom of the bead or, with
beadless finishes, the neck ring parting line.

Side Wall: The remainder of the body area between the

shoulder and the heel.

Bottom: The bottom of the container is made in the "bottom

plate" part of the glass container mold. The designated parts
of the bottom normally are:

Bearing Surface: That portion of the container on which it

rests. The bearing surface may have a special configuration
known as the "stacking feature" which is designed to provide
some interlocking of the bottom of the jar with the closure
of another jar on which it might be stacked for display
purposes.

Bottom Plate Parting Line: A horizontal mark on the glass

surface resulting from the matching of the body mold parts
with the bottom plate.

10-32
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix III

Glossary of terms - Flexible Retortable Pouches.

Adhesive: A substance applied to ply surfaces to cement the

layers together in a laminated film: (a). Polyurethane
adhesive for the outer layer (b). Maleic anhydride adduct of
polypropylene for the inner layer.

Blisters: Bubbles/gaseous inclusions/particulate material,

may be present between layers of laminate, usually are found
in the seal area.

Bottom of Closing Seal: Portion of closing (packer) seal

adjustment to the pouch contents.

Bottom Seal: A seal applied by heat and pressure to the

bottom of a flexible pouch.

Cosmetic Seal: Area above the primary seal designed to close

the edges of the pouch thus preventing the accumulation of
extraneous material.

Cuts, Punctures, Scratches: Mechanical defects that penetrate

one or more layers of the pouch.

Delamination: Any separation of plies through adhesive

failure. This may result in questionable integrity of the
package and safety of the product.

Dirty: Smeared with product or product trapped in top edges

(where there are no cosmetic seals).

Disintegrated Container: Evidence of delamination or

degradation after retorting.

Final Seal: A seal formed by heat and pressure by the packer

after pouch filling and prior to retorting.

Foil Flex Cracks/Foil Roll Holes: Visible cracks in the

aluminum foil layer caused by flexing of the pouch or pin
holes (roll holes) in the foil caused through manufacture of
the aluminum ply.

10-33
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Foreign Materials: Any material (solid food, condensate,

grease, voids, blemishes) that may be entrapped between the
plies but usually found in the seal area.

Fusion Seal: A seal formed by joining two opposing surfaces

by the application of heat and pressure.

Hard Swell or Blown: Distention or rupture due to internal

gas formation.

Inner Ply: Polypropylene coating bonded to the food surface

side of the aluminum foil.

Laminate: Two or more layers of material held together by

adhesive(s).

Leaker: Product leaking through any area of the pouch.

Outer Ply: The polyester film bonded to the exterior surface

of the aluminum foil.

Over Carton: A separate container (usually cardboard) in

which the flexible pouch is packaged for additional
protection.

Package Dimensions: The measurements of retortable flexible

pouches stated as length, the longest dimension (LGT), width
the second longest dimension (W), and thickness, the shortest
dimension (HGT). All are given as internal measurements.

Pin Holes, Roll Holes: Holes in the aluminum foil layer only,
originating during manufacturing; usually do not leak.

Preformed Seals: Seals formed by heat and pressure, by the

manufacturer of the pouches, along the sides and at the
bottom of the pouches.

Primary Seal: A fusion seal formed by the food processor by

applying heat and pressure immediately after filling.

Seal: A continuous joint of two surfaces made by fusion of

the laminated materials.

Seal Width: The maximum dimension of the seal measured from

the leading outside edge perpendicular to the inside edge of
the same seal.

10-34
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Severely Damaged: Punctures, cuts or ruptures which penetrate

all layers of the pouch and expose the product to
contamination.

Side Seals: Seals formed by applying heat and pressure to the

sides of the pouch's laminates to form the "preformed pouch".

Tear Nicks or Notch: Notches near the final seal to aid the
consumer in opening the pouch.

Wrinkle: A crease or pucker in the seal (Packer or Factory)

areas.

10-35
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix IV

Table 1. Normal pH Values for a Few Representative Canned

Meat/Poultry Products.

__________________________________________________________________

Kinds of Food pH

Beans with Wieners 5.7

Beef Chili 5.6
Beef Paté 5.7
Beef Stew 5.4 - 5.9
Beef Taco Filling 5.8
Beef and Gravy 5.9 - 6.1
Chicken Noodle Soup 5.8 - 6.5
Chicken Soup with Rice 6.7 - 7.1
Chicken Broth 6.8 - 7.0
Chicken and Dumplings 6.4
Chicken Vegetable Soup 5.6
Chicken Stew 5.6
Chicken Vienna Sausage 6.1 - 7.0
Chorizos 5.2
Corned Beef 6.2
Corned Beef Hash 5.0 - 5.7
Egg Noodles & Chicken 6.5
Ham 6.0 - 6.5
Lamb, Strained Baby Food 6.4 - 6.5
Pork Cocktail Franks 6.2
Pork with Natural Juices 6.2 - 6.4
Pork Sausage 6.1 - 6.2
Roast Beef 5.9 - 6.0
Spaghetti and Meatballs 5.0
Spaghetti Sauce with Beef 4.2
Stuffed Cabbage 5.9
Sloppy Joe 4.4
Turkey, Boned in Bouillon 6.1 - 6.2
Turkey with Gravy 6.0 - 6.3
Vienna Sausage 6.2 - 6.5
Wieners, Franks 6.2
__________________________________________________________________

10-36
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix V

Table 2. KEY TO PROBABLE CAUSE OF SPOILAGE IN CANNED FOODS

Group 1.- Low-Acid Foods

pH Range 5.0 to 8.0

Condition of Characteristics of Material in Cans

cans
Odor Appearance Gas pH Smear Cultures Diagnosis
(CO2 &
H2)
Swells Normal to Normal to frothy More than Normal Negative to Negative Hydrogen swells
"metallic" (Cans usually etched 20% H2 occasional
or corroded) organisms
Sour Frothy; possibly ropy Mostly Below Pure or mixed Growth, aerobically Leakage
brine CO2 Normal cultures of and/or anaerobically
rods, cocci, at 35°° C., and
yeasts or molds possibly at 55°° C.
Sour Frothy; possibly ropy Mostly Below Pure or mixed Growth, aerobically No process given
brine, food particles CO2 Normal cultures of and/or anaerobically
firm with uncooked rods, coccoids, at 35°° C., and
appearance cocci and possibly at 55°° C.
yeasts (If product received
high exhaust, only
spore formers may be
recovered)
Normal to Frothy H2 and Slightly to Rods, med. Gas, anaerobically Post-processing
sour- CO2 definitely Short to med. at 55°° C., and temperature abuse
cheesy below long, usually possibly slowly at Thermophilic
normal granular; 35°° C. anaerobes
spores seldom
seen
Cheesy to Usually frothy with Mostly Slightly to Rods; usually Gas anaerobically at Underprocessing -
putrid disintegration of CO2; definitely spores present 35°° C. mesophilic anaerobes
solid particles possibly below (possibility of Cl.
some H2 normal botulinum)
Slightly Normal to frothy Slightly to Rods; spores Growth, aerobically Underprocessing - B.
off – definitely occasionally and/or anaerobically subtilis type
possibly below seen with gas at 35°° C and
ammoniacal normal possibly at 55°° C.
Pellicle in aerobic
broth tubes. Spores
formed on agar and
in pellicle.

10-37
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

No Normal Normal No H2 Normal to Negative to Negative Insufficient vacuum,

vacuum slightly moderate number caused by: 1)
and/or below of organisms Incipient spoilage,
Cans normal 2) Insufficient
buckled exhaust,
3) Insufficient
blanch,
4) Improper retort
cooling procedures,
5) Over fill
Normal to Normal to cloudy Slightly to Rods, generally Growth without gas Post-Processing
Flat sour brine definitely granular in at 55°° C. Spore temperature abuse
cans below appearance; formation on Thermophilic flat
(0 to normal spores seldom nutrient agar sours.
normal seen
vacuum)
Normal to Normal to cloudy Slightly to Pure or mixed Growth, aerobically Leakage
sour brine; possibly moldy definitely cultures of and/or anaerobically
below rods, coccoids, at 35°° C., and
normal cocci or mold possibly at 55°° C.

10-38
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix VI

Table 3. KEY TO PROBABLE CAUSE OF SPOILAGE IN CANNED FOODS

Group 3. Semi-Acid Foods

pH Range 4.6 to 5.0

Condition of Characteristics of Material in Cans

cans
Odor Appearance Gas pH Smear Cultures Diagnosis
(CO2 &
H2)
Swells Normal to Normal to frothy More Normal Negative to Negative Hydrogen swells
"metallic" (Cans usually etched than occasional
or corroded) 20% H2 organisms
Sour Frothy; possibly Mostly Below Normal Pure or mixed Growth, Leakage
ropy brine CO2 cultures of aerobically
rods, coccoids, and/or
cocci, yeasts anaerobically at
or molds 35°° C., and
possibly at
55°° C.
Sour Frothy; possibly Mostly Below Normal Pure or mixed Growth, No process given
Note: ropy brine, food CO2 cultures of aerobically
Cans are particles firm with rods, coccoids, and/or
Sometimes uncooked appearance cocci and anaerobically at
flat yeasts 35°° C., and
possibly at
55°° C. (If
product received
high exhaust,
only spore
formers may be
recovered)
Normal to Frothy H2 and Slightly to Rods - med. Gas, Post-processing
sour-cheesy CO2 definitely Short to med. anaerobically at temperature abuse
below normal long, usually 55°° C., and Thermophilic
granular; possibly slowly anaerobes
spores seldom at 35°° C.
seen
Normal to Normal to frothy Mostly Normal to Rods; possibly Gas Underprocessing –
cheesy to with disintegration CO2; slightly below spores present anaerobically at mesophilic
putrid of solid particles poss- normal 35°° C. Putrid anaerobes
ibly odor (possibility of
some H2 Cl. Botulinum)

10-39
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Slightly off Normal to frothy Slightly to Rods; Growth, Under-

- possibly definitely occasionally aerobically processing - B.
ammoniacal below normal spores observed and/or subtilis type
anaerobically
with gas at 35°° C
and possibly at
55°° C. Pellicle
in aerobic broth
tubes. Spores
formed on agar
and in pellicle.
Butyric acid Frothy, large volume H2 and Definitely Rods - bipolar Gas Under
gas CO2 below normal staining; anaerobically at processing -
possibly spores 35°° C. Butyric butyric acid
acid odor anaerobe

No vacuum Normal Normal No H2 Normal to Negative to Negative Insufficient

and/or Cans slightly below moderate number vacuum, caused by:
buckled normal of organisms 1) Incipient
spoilage,
2) Insufficient
exhaust,
3) Insufficient
blanch,
4) Improper retort
cooling
procedures, 5)
Over fill
Flat cans Sour to Normal to cloudy Slightly to Rods, possibly Growth without Underprocessing B.
(0 to normal "medicinal" brine definitely granular in gas at 55°° C. and coagulans
vacuum) below normal appearance possibly at
35°° C. Growth on
thermoacidurans
agar
Normal to Normal to cloudy Slightly to Pure or mixed Growth, Leakage
sour brine; possibly definitely cultures or aerobically
moldy below normal rods, coccoid, and/or
cocci or mold anaerobically at
35°° C., and
possibly at
55°° C.

10-40
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

Appendix VII

Table 4. Characteristics of Normal and Abnormal Perishable Canned Meat/Poultry Products

Condition of Odor Appearance pH Smear Cultures Probable

Cans Cause
Flat Cans (0 to Normal Normal Normal Negative to 0 to low # APC, Normal product
Normal Vacuum) occasional APT agar count
organisms
0 to degrees of Sour to off Normal to mushy, Slightly to Mixed culture Low # mesophiles, 1. Prolonged storage
swelling odor possible gel definitely of rods & high # at low temperatures
liquification below normal enterococci psychrophilic non- 2. Abnormal high
spore formers levels in raw
(enterococci, materials 3.
lactobacilli Substandard process
Swell Sour or off Normal to mushy, Slightly to Mixed culture High # mesophilic Product held without
odor, possibly possible gel definitely of rods, cocci spore formers and refrigeration
putrid liquification below normal non-sporeformers
Swell Normal to sour Normal Below normal Cocci, rods or Enterococci, rods Leakage if shell
both or both higher than core.
Underprocessing if
core higher than
shell
Swell Off odor Normal to off Below normal Rods Psychrotrophic Low brine levels
color clostridia (rarely
occurs in U.S.).
Swell Normal to Ranges from Normal to low, Vary Vary Missed processing
putrid, uncooked depending on cycle.
depending on appearance to length of Most of these are
length of digested storage. detected soon after
storage. distribution.

10-41