Food Preservation by

Application of Heat

UNIT 3 CANNING OF FRUITS AND

VEGETABLES
Structure

3.0 Objectives
3.1 Introduction
3.2 Canning Process for Fruits and Vegetables
Principles
Process
Tin Containers
Spoilage in Canned Fruits and Vegetables
3.3 Canning of Fruits
3.4 Canning of Vegetables
3.5 Aseptic Canning of Fruit and Vegetable Products
3.6 Let Us Sum Up
3.7 Key Words
3.8 Answers to Check Your Progress Exercises
3.9 Some Useful Books

3.0 OBJECTIVES

After reading this unit, you should be able to:

• state the principles of canning;

• explain the various unit operations involved in canning;
• describe the canning process of fruits and vegetables; and
• list the cans and types of spoilages of canned products.

3.1 INTRODUCTION

You know there are several methods of preservation of fruits and vegetables
and canning is one of them. It is an important method of food preservation by
heat. In this process, the foodstuff (fruits & vegetables) are placed in
containers, and sterilized by placing them in hot water or steam. Canning is
also known as appertizing in honour of its inventor. In 1804, Nicholas Appert,
a confectioner in France, invented a process of sealing foods hermetically in
containers and sterilizing them by heat. He had also published a book entitled,
“The Art of Preserving Animal and Vegetable Substance for Many Years”,
which is the first known work on modern canning.

Canning is an important process of preservation of fruits and vegetables by

application of heat. In this unit, we will discuss canning process for fruits and
vegetables. Several unit operations are involved in the canning process. The
process discusses the principles and purpose of canning, types and causes of
spoilages. Tin cans are used in the canning of fruits and vegetables.

Fruits and vegetables are canned in the season when the raw material is
available in plenty and at low price. The canned products are sold round the
year and give better returns to the grower. Thus, canning of fruits and
vegetables is an important industry.

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 Canning of Fruits and
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3.2 CANNING PROCESS FOR FRUITS AND
VEGETABLES
Canning is defined as the preservation of foods in the sealed containers and
usually implies heat treatment as the principal factor in prevention of spoilage.
Mostly the canning is done in tin cans but other containers like glass, plastics,
etc. The fruits and vegetables used for canning should be as fresh as possible
so that their quality could be retained. Fruits should be mature, firm ripe and
free from all defects, while vegetables should be usually tender.

3.2.1 Principles
1. Destruction of spoilage organisms within the sealed containers by
application of heat,
2. To improve the texture, flavour and appearance by cooking, and
3. To stop recontamination of food during storage.
You should be careful during heat application that palatability of food is least
disturbed while all the microbial load is destroyed.
3.2.2 Process
Canning process includes the following steps or unit operations:
Selection of fruits & vegetables → Sorting & Grading → Washing → Peeling
→ Cutting → Blanching → Filling → Syruping/Brining → Lidding or
Clinching → Exhausting → Seaming → Processing → Cooling → Testing for
defects → Storage.
i) Selection of Fruits and Vegetables

We should select the fresh good quality fruits and vegetables for canning
because quality of canned product is dependent on the quality of raw
material. Fruits should be firm, mature and uniformly ripe. Over-ripe,
insect infected and diseased fruits and vegetables should be rejected.
Unripe and immature fruits should be rejected because they generally
shrivel and toughened on canning. Vegetables should be tender. Fruits
and vegetables should be free of dirt.

ii) Sorting and Grading

We should see that any spoiled, blemished, injured fruit or vegetable be

discarded. Raw material should be sorted based on maturity and
ripeness. Fruit and vegetables should be graded according to size and
colour to obtain uniform quality of canned product. Grading can be done
by hand or by machines. Screw type and roller type grader are generally
used.

Fruits like berries, cherries, grape and plum are graded whole, while
peach, pear, apricot, mango, pineapple, etc., are generally graded after
cutting into pieces.

iii) Washing

Fruits and vegetables should be washed with water thoroughly.

Washing will remove dust, dirt and any sprayed chemical residue. Any
microorganism over the surface of the fruits or vegetables are also

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washed out. Water used for washing may be cold or hot. We may
employ chlorine (150ppm) or potassium permanganate (dilute solution)
in water to disinfect fruits and vegetables. Fruits and vegetables are
generally soaked in water tank before washing by hand. They can be
washed by spraying water, which is the most effective method.

iv) Peeling

Washed fruits and vegetables are prepared for canning. The fruits and
vegetables are peeled by hand with knife or machine, heat treatment or
lye solution. Lye is a solution of caustic soda. For example, peaches and
potatoes are scaled in steam or boiling water and put in cold water to
soften and loosen or cracking of skin. Later the skin can easily be
removed by hand or pressure spray of water.

In case of lye peeling of fruits and vegetables, e.g., peaches, apricots,

orange and sweet potatoes are dipped in boiling lye (1-2% caustic soda)
for ½ to 2 minutes. Any trace of alkali is removed by washing fruits and
vegetables in running cold water; sometimes they are also washed in
water containing 0.5 per cent citric acid or hydrochloric acid.

v) Cutting

We should cut the fruits and vegetables depending upon the requirement
like slice, dice, finger etc either by knife or by machine. At the same
time seed, stone and core are also removed by special coring knife.

vi) Blanching

In blanching operations the prepared fruits and vegetables are kept in

boiling water or exposed to steam for 2 to 5 minutes followed by cooling
in running cold water. The time and temperature of blanching vary
depending on the type of raw material. Inactivation of peroxidase
enzyme is used as an index adequacy of blanching. The purposes of
blanching are: (1) to inactivate the enzymes, which cause discolouration
and off-flavour, (2) to reduce the volume by shrinkage, making their
packing easier, (3) to reduce the microbial load on raw materials, (4) to
enhance the green colour of vegetables like peas and spinach, (5) to
remove undesirable acids and astringent taste of the peel resulting
improved flavour, and (6) to remove occluded gases for reducing strain
on the seam of can during processing.

vii) Filling

Tin cans are used as containers for canning. The cans can be opened
from any end as they are called open top sanitary can. Cans are washed
with hot water. Prepared fruits and vegetables are filled into cans either
by hand or by machine. Plain cans are used generally, although in case
of coloured fruits like black grapes, red plum, strawberries, etc.,
lacquered cans are employed.

In case of canned fruits the drained weight should not be less than 50%
and for berry fruits not less than 40%. Similarly for canned vegetables
the drained weight should not be less than 55% but in case of tomatoes
limit is the 50%. Therefore, fruits and vegetables are filled about 60 per
cent of the filling capacity of a can.

viii) Syruping
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 Canning of Fruits and
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A solution of sugar in water is called syrup. Generally the fruits are
covered with sugar syrup. Cans are filled with hot (79°–82°C) sugar
syrup, leaving a headspace of 0.3 to 0.5cm. Syrup of 10° to 55° Brix
(per cent sucrose) is generally used. We can prepare sugar syrup of 20°
Brix by dissolving 250 g sugar in one-liter water and of 50oBrix by
dissolving one kg of sugar in one litre water. Sometimes citric acid and
ascorbic acid are also mixed with the syrup to improve flavour and
nutritional value, respectively. The purpose of adding syrup to fruits is
(1) to improve taste, (2) to fill up the interspaces in can, and (3) to
facilitate further processing.

ix) Brining

Brine is a solution of common salt in water. Brine is used in canning of

vegetables. A brine of 1 to 3% salt is used at 79°-82°C, leaving a
headspace of 0.3 to 0.5 cm in the can. The objectives of brining are to
improve the taste of vegetables and to facilitate further processing by
filling the interspaces of vegetables in the can.

x) Lidding or Clinching

Now the filled cans are covered loosely with the lid before exhausting. It
has some disadvantages such as spilling of the contents and toppling of
the lids. In modern canning, lidding has been replaced by clinching
operation. In this case, lid is partially seamed. The lid remains
sufficiently loose to permit the escape of gases, air and vapour formed
during exhausting operation.

xi) Exhausting

There are respiratory gases and air remain in the cans, which are to be
removed before processing. The method of removing these gases is
known as exhausting. Containers are exhausted by heating or
mechanically. In heat exhausting, the cans are passed through a tank of
hot water or exhaust box under steam. The fruit cans are exhausted at 82
to 100°C for 7-10 minutes or until temperature at the centre of the can
reaches 74°C. The vegetable cans are exhausted at 90 to 100°C for 7-10
minutes or until temperature at the centre of the can reaches 77°C. The
proper exhausting reduces the strain on the seam of the can.

The time and temperature of exhausting vary with the size and contents
of can, but it should be sufficient to ensure a vacuum of 12 to 15 inch
Hg in processed and cooled can.

xii) Sealing or Seaming

After exhausting, the cans are sealed by double seaming machine and
the method is called seaming. In sealing lids on cans, a double seam is
created, and the method of sealing or closing is also known as seaming.

xiii) Processing

Process of heating and cooling of canned food to inactivate bacteria and

to preserve food is also called as commercial sterilization. Many
bacterial spores are heat resistant, which can only be killed either by
very high or by very low temperature treatment or prolonged cooking.
Such drastic treatment, however, affects the quality of food. Thus,

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processing time and temperature should be adequate to eliminate all
bacterial growth. We must not over-cook the canned foods otherwise it
will spoil the flavour, appearance and texture of the product.

All fruits and acid vegetables can be processed satisfactorily at a

temperature of 100°C, i.e., in boiling water. The acid present in fruits
and acid vegetables retards the growth of bacteria and spores. These
bacteria and spores do not thrive in heavy sugar syrups, which are
normally used in canning fruits. Vegetables, generally non acidic
(except tomato and rhubarb), are processed at a higher temperatures of
about 115 to 121°C.

Bacterial spores usually do not grow below pH 4.5 as you have read in
previous chapters. We, generally process the canned products having pH
less than 4.5 in boiling water but products with pH higher than 4.5
require processing at 115 to 121°C. The higher temperature can be
obtained by processing in a retort under a pressure of 0.70 to 1.05
kg/cm2 (10 to 15 lb/sq. inch). The centre of can should attain these high
temperatures.

The temperature and time of processing vary with the size of the can, the
larger the can, the greater is the processing time. Fruits and acid
vegetables are generally processed in open type cookers, continuous
non-agitating cookers and continuous agitating cookers.

The open cookers are galvanized iron tank of desired capacity. Sealed
cans are placed in iron crates and immersed in the tank containing
boiling water. In continuous cookers, the cans travel in boiling water in
crates carried by overhead conveyors. In continuous agitated cookers,
the cans are rotated by special mechanical devices to agitate the contents
of the cans. Agitation reduces the processing time considerably.

The non-acid vegetables are processed under steam pressure in closed

retorts. The sealed cans are placed in the retort, keeping the level of
water 2.5 to 5.0 cm above the top of the cans. The cover of the cooker is
then screwed down tightly and the cooker is heated by steam to the
desired temperature. The period of processing (sterilization) should be
counted from the time the water starts boiling or steaming. After
heating for the required period, heating is stopped and the petcock or
vent is opened. When the pressure comes down to zero the cover is
removed and the cans are taken out.

xiv) Cooling

After processing, the cans are cooled rapidly to about 39°C to stop the
cooking process. Cooling can be done by several methods such as
(1) immersing the hot cans in tank containing cold water, (2) spraying
cold water, (3) turning in cold water into the pressure cooker, and
(4) exposing the cans to air. Generally the first method is practiced.
Cooling water may be kept sterile with 1 or 2 per cent chlorine. If
canned products are not cool immediately after processing, the quality is
deteriorated, e.g., peaches and pears become dark in colour, tomatoes
turn brownish and become bitter in taste, while peas become mashy with
a cooked taste.

xv) Testing for Defects

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Before the canned products are marketed, we should test them for any
defect. The finished cans are tested for leak or imperfect seals. We
should tap the top of the can with a short steel rod. A clear ringing
sound indicates a perfect seal, while a dull and hollow sound shows a
leaky or imperfect seal. Leaky cans should be removed from the lot.

xvi) Storage, labelling and packing

Before storage, the cans should be completely dry, small traces of

moisture are likely to induce rusting. They should be stored in a cool
and dry place. Storage of cans at high temperature should be avoided, as
it shortens the shelf life of the product. The high temperature may lead
to hydrogen swell and perforation during extended storage. The
basement stores are useful, especially during summer months. The
temperature in these stores is lower by about 6° to 8°C, compared to
outside temperature. Before dispatch, the cans are labelled and packed
either in wooden or cardboard boxes, and are ready for marketing. The
cans may be stored for 1 to 2 years depending upon the type of raw
materials used and the shelf life of the product.

3.2.3 Tin Containers

The cans are made of thin steel plate of low carbon content, lightly coated on
both sides with tin metal. Sometimes discolouration of the product or
corrosion of the tin plate takes place. In order to avoid corrosion, these cans
are coated inside and or outside with lacquer, the process is known as
“lacquering”. There are two types of lacquers used.

1. Acid-resistant-Acid-resistant lacquer is a golden colour enamel, cans

coated with it are called R enamel or A.R. cans. The lacquered cans are
used for packing fruits having water soluble colour (anthocyanins) for
example raspberry, strawberry, red plum, coloured grapes, pomegranate,
etc. Fruits having water insoluble colour, for example pineapple, mango,
grapefruit, etc., are packed in plain cans only.

2. Sulphur-resistant – This lacquer is also of a golden colour, cans coated

with it are called C. enamel or S.R. cans. These cans are used for packing
pea, corn, lima beans, etc.

The tin cans are supplied to the canning factory in flattened form, where they
are reformed using a machine, reformer, into cylindrical shape. After that,
they are flanged by using flanger, which curls the rings outwards at each end.
The one end of the cylindrical can is then fixed, before filling it, using a
machine known as double seamer. After filling, processing and exhausting the
can, the lid is fixed using the same machine.
Table 3.1: Commercial can sizes and capacities

Sl. Trade name of can Size (mm) Capacity (in

No. cubic cm)
1. A1 68 × 102 316
2. 1-1b Jam 78 × 90 356
3. A1-T 78 × 119 479
4. A2 87 × 114 579

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5. 1-1b Butter 103 × 70 470
6. A2-1b Jam 103 × 102 721
7. A2½ 103 × 119 848
8. 7-1b Jam 157 × 148 2543
9. A10 157 × 178 3069

3.2.4 Spoilage in Canned Fruits and Vegetables

Canned products are liable to spoilage for various reasons. Spoilage in canned
food may be caused due to two reasons:
A) Spoilage due to physical and chemical changes:
1. Swell – Swell or bulge in cans caused due to the positive internal
pressure of gases formed by microbial or chemical action. Hydrogen
Swell – This type of swelling is due to the hydrogen gas produced by
the action of food acids on the metal of the can. The swelling ranges
from flipper – springer, soft swell or hard swell.
2. Overfilling – Overfilling should be avoided.
3. Faulty retort operation – It gives cans look like swells.
4. Under exhausting – It causes severe strain during heat processing.
5. Panelling – It is seen in large sized cans that the body is pushed inward
due to high vacuum inside.
6. Rust – Rust is mostly seen under the label and subsequently affects the
label. Cans lacquered externally do not rust.
7. Leakage – Cans generally leak due to defective seaming and nail holes.
8. Bursting – Cans may burst due to excess pressure of gases produced by
decomposition of the food.
9. Discolouration – This may be due to enzymatic and non – enzymatic
browning. Enzymatic discolouration can be avoided by placing the
peeled and cut pieces of fruits and vegetables in 2% salt solution.
10. Stack burning – The contents in the can if remain hot for a long time
during storage result in stack burning. It may cause discolouration. To
avoid stack burning cans should be cooled quickly to about 39oC
before storage.
B) Spoilage by microorganisms
The time gap between filling and heat processing may cause microbial
spoilage. If cans are not processed properly they may result in spoilage by
bacteria and the spoilage is termed as “Under processed” spoilage.
Various spoilages caused due to different microorganisms are:
1. Flat sour – The non-acid vegetables spoiled by Bacillus coagulens and
Bacillus sterothermophilus.
2. Thermophilic acid spoilage – Cans swell due to production of carbon
dioxide and hydrogen by Clostridium thermosaccharolyticum.

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3. Sulphide spoilage – Caused by Clostridium nignificans in low acid
foods.
So, we should process cans properly to avoid any type of spoilage.

Check Your Progress Exercise 1 "

Note: a) Use the space below for your answer.
b) Compare your answers with those given at the end of the unit.
1. Define principles of processing.
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2. List the name of unit operations involved in the canning process.
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3. State the differences between processing of fruits and vegetables in a can.
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Food Preservation by
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4. Describe the causes and types of spoilages of canned foods?
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3.3 CANNING OF FRUITS

The fruits are exhausted at 82 to 100oC for 7-10 minutes or until the centre of
the can reaches at least 74oC temperature. The types of can, strength of
covering sugar syrup and time-temperature for No.2½ and No.10 cans are
summarised in Table 3.2.
Table 3.2: Canning time table for fruits and tomatoes

Sl. Fruit Type of Strength of Processing time (min)

No. can syrup in boiling water at
(Degree Brix) 100°C

No.2½ No. 10

1. Apple Plain Water or light 12 25

syrup
2. Apricot Plain 55 35 50
3. Banana Plain 30+0.2% 20 −
citric acid
4. Blackberry Fruit 55 20 30
lacquered
5. Cherry Fruit 40 20 25
(sweet) lacquered
6. Cherry (sour) Fruit 45 20 25
lacquered
7. Fig Plain 55 15 35
8. Grape Fruit 40 12 15
(coloured) lacquered
9. Grape (white) Plain 40 12 15
10. Grape fruit Plain 60 30to 40

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11. Guava Plain 40 20 −
12. Jack fruit Plain 50 30 −
13. Litchi Plain 40 30 −
14. Mango Plain 40 30 −
15. Mulberry Fruit 40 12 −
(coloured) lacquered
16. Musk Melon Plain 40+0.3% 30 −
Citric acid
17. Orange Plain 50 15 to 20
18. Papaya Plain 45 30 −
19. Peach Plain 55 30 50
20. Pear Plain 40 35 60
21. Pineapple Plain 40 30 60
22. Plum, red Fruit 40 20 30
lacquered
23. Raspberry Fruit 45 12 25
lacquered
25. Strawberry Fruit 50 15 20
lacquered
26. Tomato Plain Only tomato 30 70
juice in the
case of
standard pack
27. Fruit Cocktail Plain 45 30 90
(Fruit salad)

i) Apple
Apples are generally not canned. However, canned apples available in
the large sizes of cans are used in pies. The varieties used for canning
are: Golden Delicious, Yellow Newton, Baldwin, Jonathan, and Ambri.
The fruits should be washed in warm dilute hydrochloric acid (0.5%)
solution to remove any residue of lead or arsenic sprays. And then
washed thoroughly in cold water to remove traces of acid. The apples
are peeled by hand or machine and cut into 0.3 to 0.6 cm thick slices.
The prepared fruits should be kept in 2 to 3 per cent common salt
solution to avoid darkening due to enzyme action. The prepared fruits
are blanched in hot water at 71 to 81o C for 3 to 4 minutes and then
cooled in water. Blanching removes the air and gases and inactivates
enzymes. The blanched fruits are filled into cans, covered with hot
water or thin sugar syrup, exhausted, sealed and processed.
ii) Apricot
Apricots are mostly grown in Kashmir, Himachal Pradesh and
Uttaranchal, where a great scope exists for their canning. Charmagz and
Shakarkand are white sweet varieties which are good for canning.
Apricots are either canned whole or halves.
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iii) Banana
South Indian varieties of banana, viz. Pachabale, Chandrabale, Nendran,
Poovan and Vannan are good for canning. Fully ripe bananas are
selected for canning. Fruits are peeled by hand and then cut into long
slices of 1 to 2 cm thickness. The slices are filled into cans and covered
with a sugar syrup of 25 to 30° Brix containing 0.2 per cent citric acid.
Then the cans are exhausted, sealed and processed.
iv) Ber
Umran and Katha varieties of ber are good for canning. Fully mature
fruits are selected for canning. Peel is removed by hand with the help of
stainless steel knife or by dipping in 5 per cent boiling hot caustic soda
solution for 2 minutes and then washed in running tap water. Second
washing is done in water containing 0.1 per cent citric acid in order to
remove any traces of caustic soda solution. The fruits are cut into slices.
The slices are filled into one lb Jam size can, exhausted; sealed,
processed in boiling water for 20 minutes and cooled.
v) Berry Fruits
Among berry fruits, strawberry, loganberry, black berry, raspberry,
mulberry and black and red currants are popular for canning. White
heart cherry and red cherry having creamy white flesh, are good for
canning. Maraschino cherries are canned for mixing with other fruits
and for fruit cocktails.
The cherries for canning are generally decolourised during curing in
brine for 4-6 weeks. During curing cherries are kept in a brine, which is
made up of about 0.75 to 1.0 per cent sulphur dioxide (SO2) and about
0.4 to 0.6 per cent slaked lime. The cured cherries are washed well in
water and dyed with a red dye like Erythrosine, and the colour is fixed
with citric acid. These cherries are used for canning.
vi) Citrus Fruits
Generally grape fruit and oranges are canned. Grape fruit varieties
Marsh Seedless, Duncan and Foster are good for canning. The fruit is
immersed in hot water (93 to 96°C) for 2 to 5 minutes. It softens the
peel, which can easily be removed by hand. The peeled fruit is further
hand peeled or lye-peeled to remove the white rag portion called albedo.
For lye peeling, the whole fruit is immersed in hot lye solution
containing 1.5 to 2.0 per cent caustic soda (NaOH) for 20 to 30 seconds.
It is then washed with cold water and the segments are separated. The
membranes and seeds are removed with the help of knife. The prepared
segments are filled into plain cans, and then filled with 60° Brix syrup.
The filled cans are exhausted for 25 to 30 minutes at 82 to 87°C, then
sealed and processed for 30 to 40 minutes at the same temperature. The
cans are cooled immediately after processing.
Satsuma, Mandarin and Unshu (in Japan) are employed for canning.
Malta and Sathgudi, which are tight skin, and loose jacket Nagpur and
Coorg oranges also yield good canned products.
The peel of loose jacket orange is removed by hand easily. The peel of
tight skin oranges is removed and prepared similar to grape fruit. The
filled cans are exhausted for 15 to 20 minutes at 82 to 87°C, sealed and

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pressed for another 15 to 20 minutes at the same temperature in open
cooker. After processing, the cans are cooled immediately in cold
water.
vii) Grape
Grape varieties such as Thompson Seedless and Muscat are good for
canning. Only large sized berries are used for canning. Washed berries
are filled into cans and covered with syrup of 20 to 40° Brix. The cans
are exhausted, sealed and processed. The coloured grapes should be
canned in lacquered cans.
viii) Guava
Fully ripe but firm fruit, with white flesh, are selected for canning.
Fruits are peeled by knife or by lye solution as described above. Peeled
fruits are cut into halves and seeds are scooped out with a spoon-shaped
knife. The prepared fruit should be immersed in 1 to 2 per cent common
salt solution. It helps to prevent the fruit from browning. Either halved
or quarters are canned. The peel and core with seeds can be used for
making guava jelly or guava cheese. Canned guava has a taste and
aroma better than those of fresh fruits.
ix) Jack-Fruit
Jackfruit is mostly available in Maharashtra, Bihar, Orissa, Karnataka,
Kerala and Tamilnadu. In these states, certain sections of the people use
it as an important staple food. All parts of the fruit can be used in one or
the other form of food. The green and immature fruit can be canned as a
curried vegetable. The ripe fruit with the crisp bulb after seed removal
is used for canning in sugar syrup.
The fruit is washed, cut into several large pieces and the bulbs are
removed with hand. The fruit contains a white, highly sticky, latex so, a
little vegetable oil such as til or gingelly oil, is smeared on the hand and
the knife to prevent the latex from sticking on them. The latex is soluble
in oil. The bulb after seed removal is canned as a whole, halved or
quarter. Generally syrup of 50° Brix having 0.5 to 0.75 per cent citric
acid is used for canning of jackfruit bulb.
x) Litchi
Litchis are mostly cultivated in Bihar, Orissa, Uttaranchal and Uttar
Pradesh. Tree-ripened fruit is selected for canning. Fruit is washed,
skin is removed, and aril is separated from stones. The aril is filled in
cans, and aril covered with sugar syrup of about 40o Brix containing 0.5
per cent citric acid. The filled cans are exhausted, sealed and then
processed as mentioned earlier. After processing, cans are cooled
promptly and thoroughly in running cold water to prevent development
of pink colour in the product.
xi) Mango
In India, Uttar Pradesh, Tamil Nadu, Andhra Pradesh, Karnataka, Bihar,
Maharashtra and West Bengal lead in mango cultivation. Dashehari,
Alphonso, Badami, Baneshan, Raspuri, Neelam, Mulgoa and Totapuri or
Bangalora are the most important mango varieties for canning. Juicy
and fibrous varieties are not suitable for canning.

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Fully developed and mature fruits are harvested and ripened. Canning
ripe (just ripe but firm) fruits are selected, washed with water and peeled
by hand with the help of knife. The pulp is either cut into two broad
side (Chick) or quartered or 6 to 8 cm longitudinal slices.
The prepared fruit is placed in two per cent common salt solution to
prevent enzymatic browning. The fruit has slightly higher pH than the
critical pH of 4.2 so it is necessary to add 0.3 to 0.5 per cent citric acid
in the syrup in order to process in open cookers. The trimmings of the
slices, pulp adhering to the peel and stone can be used profitably for the
preparation of mango juice or beverages and mango jam.
xii) Papaya
Fruit is washed, peeled, seed removed and cut into slices or cubes for
canning. The fruit pulp has a high pH value so it is necessary to add 0.5
per cent citric acid in the syrup to reduce the pH below 4.5. Sometimes
papaya is canned with other fruits like pineapple, mango, banana, etc., to
produce fruit cocktails.
xiii) Peach
There are two types of peaches, one the clingstone, where the pulp
adheres to the stone tightly, and the other freestone where the pulp
adheres to the stone loosely or freely. Among the clingstone peaches,
Tuscan, Palora and Philips Cling are the varieties good for canning.
Among the freestone peaches, Elberta, Lovell and J.H. Hale are suitable
varieties for canning.
The fruits are cut into two halves and the pits removed. In large
canneries, mechanically operated knives are used to cut fruit into halves
and to remove the pits. The cut halves are peeled by immersing them in
boiling lye solution containing 1 to 2 per cent caustic soda for ½ to 1
minute. The loosened peel is removed by washing with water. The
prepared halves are filled in cans, covered with syrup, exhausted and
processed in open cooker. Sometimes peach slices are also canned.
Peaches are also used as an important constituent of fruit cocktail.
xiv) Pear
Pears are cultivated in Himachal Pradesh, Kashmir, Uttaranchal and
hilly areas of South India. Pears are harvested fully mature, firm but
green. The fruits are ripened at room temperature (23 – 26o C) and soft
fruits are used for canning.
The fruit is peeled with a knife and cut longitudinally into two halves.
The core is removed by coring knife. The prepared fruit is placed in 1 to
2 per cent common salt solution to prevent browning. The halves are
then filled into cans, covered with hot sugar syrup, exhausted, seamed
and processed as usual. The cans should be cooled immediately in cold
water to prevent development of pink discolouration of the fruit during
storage.
xv) Pineapple
Pineapple is mostly grown in Assam, West Bengal, the West Coast of
India, Andhra Pradesh and Karnataka states. Giant Kew and Queen are
the two important varieties of pineapple employed for canning.

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The fully mature and just ripe fruit is selected for canning. Uniform size
graded fruits are peeled, cored and sliced on a Ginaca machine in
foreign countries. In India, the fruits are sliced, and then core and peel
is removed by hand with the help of coring and punching knife. Slices
are graded usually for size. Since the fruit contains highly active
proteolytic enzymes, injurious to skin, the workers should wear rubber
gloves. The slices are filled into cans, covered with syrup, exhausted,
seamed, processed and cooled as usual.
xvi) Plum
The Red Victoria and the Yellow Pershore plums are important canning
varieties. The Alubukhara plum generally grown in North India, also
gives a fairly good canned product.
Generally whole plum with stone is canned. Since plum contains water-
soluble red colour, which is due to the presence of anthocyanins, is
canned in lacquered cans. Washed fruits are filled into can, either as
discrete number or by weight, covered with syrup and processed as
usual.
xvii) Other Fruits
There are some minor and lesser-known fruits such as. Date,
Pomegranate, Mulberry, Musk melon, Water Melon, Aonla, Carambola,
Tamarind, Avocado, Custard Apple, Karonda, etc. which may also be
canned as usual. These fruits may be canned as slices, cubes or juice and
pulp or beverages.

Check Your Progress Exercise 2 "

Note: a) Use the space below for your answer.
b) Compare your answers with those given at the end of the unit.
1. Why citric acid is added to covering syrup?
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.
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2. State reason for placing the prepared fruits in common salt solution.
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.

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Food Preservation by
Application of Heat
………………………………………………………………………………
.
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3. Why fruits are processed in open cooker?
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3.4 CANNING OF VEGETABLES

The vegetables are exhausted at 90-100°C for 7-10 minutes or until the centre
of the can reaches at least 77°C temperature. The types of can, strength of
covering brine and time-temperature for No.2½ and No.10 cans are
summarised in Table 3.3.
Table 3.3: Canning time table for non-acid vegetables

Sl. Vegetables Type of Strength of Processing time min. at

No. can Brine 0.7 kg per cm2 steam
(common pressure
salt)
No. 2½ Can No. 10 Can
1. Asparagus Plain 2.25% 24 40
2. Bean Plain 2.25% 40 75
3. Beet-root Sulphur Water or 30 40
resistant 1.5% Brine
4. Cabbage Plain 2% 40 60
5. Carrot Plain 2% 25 50
6. Cauliflower Plain 2% 20 −
7. Curried Plain
− 60 to 70
vegetables
8. Mushroom Plain 2% “ 25 40
9. Okra Plain 2% “ 35 −

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 Canning of Fruits and
Vegetables
10. Pea, garden Sulphur 2% Brine & 45 60
resistant 2.5% sugar
solution
11. Potato Plain 2% 45 −
12. Turnip Plain 2% 35 50

i) Asparagus
he asparagus shoots are green and white. The tender shoots are used for
canning. Just after harvesting the shoots are washed and graded for size
and cut according to the height of the can. Shoots are blanched in
boiling water for 2-3 minutes then placed in cold water. The blanched
shoots are filled into sulphur-resistant cans, covered with 2.0 per cent
common salt solution, exhausted, seamed and processed as usual.
ii) Beans
French beans, which are tendered and stringless are used for canning.
The beans are washed thoroughly with water and cut into slices about
2.5 cm in length. The slices are blanched in boiling water, drained and
filled into plain cans. The beans in the cans are covered with 2 per cent
brine, exhausted, closed and processed under pressure in retorts.
Sometimes diced beans with diced carrots and garden peas are also
canned as mixed vegetables.
iii) Beetroot
Beetroot is washed with water thoroughly. The top and roots are
removed with a stainless steel knife. The vegetable is cut in the form of
discs or cubes and placed in 1 to 2 per cent common salt solution to
preserve the colour. The prepared pieces are filled into vegetable
lacquered cans, covered with 2 per cent brine, exhausted, seamed and
processed as usual.
iv) Cabbage
Cabbage head with tender yellow leaves is used for canning. After
washing, the head is cut into 4 to 8 pieces or shredded into 2.5 cm thick
pieces. The pieces are generally blanched in boiling water for 5 to 7
minutes. The blanching water may preferably contain 1 per cent citric
acid. After blanching it is cooled in 2 per cent brine to prevent
discolouration. The prepared vegetable is filled into plain cans, covered
with 2 per cent brine and processed as usual.
v) Carrot
Generally yellow varieties of carrot are used for canning. Tender and
small carrots are selected for canning. The carrots are washed well and
skin is scrapped with a knife. For large-scale work, mechanical peeler is
employed. The peeled carrot is graded for size and used as such or cut
into discs or cubes for canning. The carrot is blanched in boiling water
for 8 to 12 minutes and packed into plain cans. Brine is used for
canning.
vi) Cauliflower
In case of cauliflower, compact flower head is selected and cut into
pieces of suitable size. The pieces are canned similar to that of cabbage.

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Food Preservation by
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vii) Mushroom
Edible mushrooms, which are not poisonous, are selected for canning.
Button mushroom is generally canned whole. Sometimes, mushroom is
bleached to a pale colour in a solution of sodium sulphite and citric acid.
They are washed with water and blanched in boiling water for 4 to
5 minutes and subsequently dipped in cold water to prevent
discolouration. Blanched mushrooms are filled into plain cans, covered
with 2 per cent hot brine, exhausted, seamed, processed as usual.
viii) Okra
Okra is also known as Lady’s finger. Tender green okras of uniform
size are selected. Okra is canned as a whole or as slices. These are
washed and blanched in boiling water for 1 to 2 minute and then cooled
in brine containing 1.5 per cent common salt. This helps in removal of
mucilage. The blanched okras are filled into plain cans and covered
with 2 per cent brine, exhausted, seamed and processed as usual.
Sometimes, the okras are also canned with thick tomato sauce in order to
overcome the mucilaginous property.
ix) Peas
Bonneville is the most popular pea variety for canning in India. We
should see that the peas for canning are uniformly ripe and should retain
the green colour even after processing. They should also possess good
texture and flavour. Large size peas are generally preferred for canning.
Peas are shelled by pea-podding machine and graded by size using
sieves with mesh ranging from 0.7 to 1.0 cm. The graded peas are
blanched in boiling water for 2 to 5 minutes, and rinsed in cold water.
They are filled into plain cans by hand or machine and covered with 2
per cent brine. Sometimes, 2 per cent cane sugar is also added in brine
to improve the flavour of the peas. An edible and FPO permitted green
colour also may be added to the brine. The cans are exhaussted, closed
and processed in a retort as usual. Canned fresh peas are generally
known as ‘green peas’ or ‘garden peas’. Dried peas are also canned. The
dried peas, which are soaked in water, are canned similar to fresh peas.
The dried canned peas are known as ‘processed’ peas.
x) Potato
Potatoes are canned either whole or slices. Good starchy and firm
potatoes are selected and washed to remove the adhered soil. Potatoes
are peeled with a knife or by potato peeler, a machine having abrasive
surface to remove peel. Peeled potatoes are kept in 2 per cent common
salt solution to prevent discolouration. Peeled potatoes are blanched in
boiling water for 5 to 7 minutes. Blanched pieces are filled into plain
cans, covered with 2 per cent brine, exhausted, seamed, processed and
cooled as usual. Some varieties of potato turn bitter after canning,
which should not be used.
xi) Tomato
Tomatoes for canning should be firm ripe, medium in size, regular in
shape, and of uniform red colour. Tomatoes should have plenty of pulp
and free from blemishes.

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 Canning of Fruits and
Vegetables
Tomatoes after washing are placed in boiling water or steam for 2 to
3 minutes to crack the skin and then washed in cold water to remove
peel easily. Any green patch is trimmed out. The peeled and trimmed
tomatoes are filled into plain cans and covered with tomato juice; and
after exhausting and seaming processed in open cooker. It’s processing
is different from other vegetables as it is acid food.

xii) Turnip
Turnips are red, white and yellow in colour but generally white turnips
are canned. Select fibre free tender turnips. They are washed thoroughly
with water and cut into about 1 cm thick slices. The pieces are blanched
in boiling water for 3 to 5 minutes and cooled. The blanched turnips are
filled into cans, covered with 2 per cent brine and processed in retort as
usual.
xiii) Other Vegetables
There are several other vegetables, which may be canned similar to the
methods given above. They are Karela, Tinda and Parwal. Spinach
(Palak) is also canned as puree.
Sarson-ka-Saag (Mustard Green)
Sarson-ka-saag is generally prepared from mustard leaves and spinach in
the ratio of 4:1. It has good demand as canned product in India and
abroad. The tender shoots of green mustard and spinach are washed,
chopped and cooked with salt for 40-45 min. Then mashing is done
along with the addition of corn flour or Bengal gram flour (besan). The
mass, then fried along with other ingredients and filled into cans,
exhausted for 10 minutes and sealed. The cans are processed for 50
minutes in a retort at 0.7 kg/cm2 and cooled to room temperature. A
general recipe for canning of sarson-ka-saag is given below:
Mustard green chopped 800g
Spinach chopped 200g
Tomato 100g
Onion 100g
Garlic 20g
Ginger 80g
Ghee/Oil 100g
Salt (to taste) 15g
Chilli 10g
Corn flour or besan 50g
xiv) Curried Vegetables
Canning of vegetables in brine is a western way of preserving and
consuming. There are certain vegetables that are canned as we cook
them along with spices and condiments. Certain vegetables like potato,
cauliflower, peas, tomatoes are cooked in combination or alone and
canned as curried vegetables. Curried vegetables are those vegetables,
which are canned along with spices and condiments such as mustard,

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Food Preservation by
Application of Heat
coriander, red chilli, turmeric, common salt and vegetable oil in form of
gravy. The curried vegetables are readily consumed after heating in the
cans. In order to prepare the curried vegetables, the oil is heated in a
pan, the mustard seed is fried in it, then other ingredients in powder
form are added to taste (as done at home while cooking vegetables) and
heatings continued. Then required amount of water is added and brought
to boil. The curried vegetables are filled into can along with gravy,
closed and processed for 60 to 70 minutes at 0.7 kg/cm2 in a retort.

# Check Your Progress Exercise 3

Note: a) Use the space below for your answer.
b) Compare your answers with those given at the end of the unit.
1. Why non-acidic vegetables are processed at high temperature in a retort?
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.
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2. Why certain vegetables are not packed in plain cans. Give names and
reasons?
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3.5 ASEPTIC CANNING OF FRUIT AND VEGETABLE

PRODUCTS
Fruit and vegetable products are packed by using the latest developed
technique known as aseptic canning. As you know that this system is basically

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 Canning of Fruits and
Vegetables
a high temperature short time (HTST) sterilizing process. This method
combines flash sterilization and cooling with aseptic methods of packaging for
fluid and semi-fluid products, thus eliminating retorting and cooling. It is
being used commercially particularly for bulk packing of products. This
system has advantage that quality of the product is maintained better. The
nutrient losses are minimum due to HTST processing and shelf life of the
product is more.

3.6 LET US SUM UP

Canning is a method of preservation of fruits and vegetables by heat
application. The main principle of canning is the destruction of spoilage
microorganisms. The canning process includes several unit operations, viz.
selection, sorting, grading, washing, peeling, cutting, blanching, filling,
syruping or brining, lidding or clinching, exhausting, seaming, processing,
cooling and storage. Fruits and vegetables differ in the canning process due to
their acid value.
Tin cans of different sizes are used for packing of fruits and vegetables. For
some fruits and vegetables lacquer cans are used. If cans are not processed
adequately they develop some defects. The defects may be caused by physical
and chemical changes, and by microorganisms. Canned products can be stored
for 1 to 2 years depending on the quality of raw materials.

3.7 KEY WORDS

Blanching : Blanching is done by immersing fruits and
vegetables in hot water or by exposing to steam
followed by cooling.
Syruping or brining : After placing prepared fruits or vegetables in
can, syrup or brine is added, respectively is
called syruping or brining.
Exhausting : The vacuum in the can obtained by heat
treatment or by mechanical means is known as
exhausting.
Seaming : It is sealing or closing of lids on cans by double
seamer. Interlocking of curl of the lid and flange
of the can creates double seam.
Processing : The application of heat to fruits and vegetables
after hermetic (air tight) sealing in containers is
called processing.
Commercial
sterilization : It is the term used for those thermally processed
products in which microorganisms and their
spores do not grow under normal conditions of
storage.
Principle purpose
of canning : Destruction of spoilage or pathogenic
microorganisms and retention the original
characteristics of food.

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Food Preservation by
Application of Heat
Unit operation : It is one of the steps in a complete process or a
physical change in form or place, for example,
peeling, cutting, grading, etc.

3.8 ANSWERS TO CHECK YOUR PROGRESS "

EXERCISES

Check Your Progress Exercise 1

Your answer should include the following points:

1. • Destruction of microorganisms, which may cause spoilage of foods.

• Improve the flavour, texture and appearance of food by cooking.
• Prevent recontamination.

2. Selection of fruits and vegetables → Sorting and Grading → Washing →

Peeling → Cutting → Blanching→ Filling → Syruping →
Lidding/Brining or Clinching → Exhausting → Seaming → Processing →
Cooling → Testing for defects → Storage

3. • Fruits are covered with sugar syrup while vegetables are covered with
brine
• Fruits are processed at 100°C while vegetables are processed at 115° to
121°C.
• Fruits are processed in open cookers while vegetables are processed in
retort under pressure( 0.7kg/cm2)

4. i) Spoilage due to physical and chemical changes:

• Swell – Hydrogen swell; Flipper, Springer, etc.

• Overfilling, faulty retort operation, under exhausting, panelling,
rust, leakage, bursting, discolouration and stack burning

ii) Spoilage by microorganisms

• Flat sour.
• Thermophilic acid sour
• Sulphur spoilage, etc.

Check Your Progress Exercise 2

1. Your answer should include the following points:

• To lower the pH of canned fruit

• To improve the palatability of canned product

2. Your answer should include the following points:

• To prevent enzymatic browning

• To prevent darkening
• To prevent discolouration

3. Your answer should include the following points:

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 Canning of Fruits and
Vegetables

• In open cooker, normal atmosphere is maintained

• In open cooker temperature of boiling water remain & below 100°C
and never increases.
• The fruits and tomato (acidic vegetables) are cooked generally in the
open cooker.

Check Your Progress Exercise 3

1. Your answer should include the following points:

• Vegetables are generally non acidic in nature

• The pH of non acidic vegetables are above 4.5
• Non-acidic vegetables are processed at high temperature
• High temperature can only be attained when processed under pressure
in a retort.

2. Your answer should include the following points:

• Certain vegetables contain water soluble colour

• Presence of anthocyanins
• Presence of sulphur compound
• Asparagus, Beetroot, Peas are packed in lacquered cans

3.9 SOME USEFUL BOOKS

1. Cruess, W.V. (1997) Commercial Fruit and Vegetable Products, Allied
Scientific Publishers.
2. Lal, G., Siddappa, G.S. and Tandon, G.L. (1986) Preservation of Fruits
and Vegetables, Indian Council of Agricultural Research, New Delhi.
3. Luh, B.S. and Woodrof, J.G. (1988) Commercial Vegetable Processing,
The AVI Publishing Company, INC; Westport, Connecticut.
4. Ranganna, S. (2000) Hand Book of Canning and Aseptic Packaging, Tata
McGraw-Hill Publishing Company Limited, New Delhi.
5. Srivastava, R.P. and Kumar, Sanjeev (1998) Fruit and Vegetable
Preservation, (Principles & Practical), International Book Distributing Co.,
Lucknow.
6. Verma, L.R. and Joshi, V.K. (2000) Post Harvest Technology of Fruits
and Vegetables Vol. 2, Indus Publishing Company, New Delhi.
7. Woodroof, J.G. and Luh, B.S. (1986) Commercial Fruit-Processing, The
AVI Publishing Company; Westport, Connecticut.

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