Lecture 6:

Milk and Milk Products

(Dairy Products)

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 Table of Contents

1. Introduction

2. Fluid Milk and Some of its Derivatives

3. Ice Cream and Related Products

4. Cheese

5. Reduced Fat Dairy Products

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 1. Introduction
• We will discuss about the properties and processing of
① Fluid milk
② Some of the more common products manufactured from fluid milk
➢ Specialty milks
➢ Ice cream
➢ Cheese
➢ Butter

• Milk is consumed as
✓ Fluid milk with minimal processing
- daily production of milk = 30 kg/day/cow (5000~6000 kg/year/cow)
✓ The raw material used to make a wide variety of other products

• Milk is commonly pasteurized and homogenized, and its

composition is very close to what it was when taken from the cow.

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 1. Introduction

• Milk can be separated into its principal components, cream and

skim milk, which may be further separated into butterfat, casein
and other milk proteins, and lactose.

• Milk can be modified by condensing, drying, flavoring, fortifying,

demineralizing, etc.

• Whole milk or its components may be combined with other food

product to make various kinds of products, such as milk
chocolate, bread, cakes, sausage, confectionery items, soups,
etc.

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 2. Fluid Milk and Some of Its Derivatives

• Table 13.1: Typical analyses of milks produced by various

animals and used for human food
• Cow milk is principal source for human consumption in U.S.
and many other countries in the world.
• Meanwhile, buffalo milk in India, goat and sheep milks in
southern Europe, and reindeer milk in Lapland

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 2. Fluid Milk and Some of Its Derivatives
• Milk constituents: fat, protein (casein), milk sugar or lactose,
minerals (ash)

• These constituents vary not only in amounts among different

animal species, but also somewhat in chemical, physical and
biological properties.

(ex.)
✓ Fatty acids of goat milk fat have different melting points,
susceptibility to oxidation, and flavor characteristics from fatty
acids of cow milk.

✓ Milk protein of various species may differ with respect to heat

sensitivity, nutritional properties, and ability to produce allergic
reactions in other species.
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 2. Fluid Milk and Some of Its Derivatives
• Cow milk will vary in composition, depending on many factors:
✓ Breed ✓ Feed
✓ Animal-to-animal variability ✓ Time of milking
✓ Age ✓ Period of time between milking
✓ Stage of lactation, season of year
✓ Cow’s physiological condition (calm or excited)

• All of these factors affect the quality of milk.

• Approximate composition of milk

➢ Total solids: 13%

➢ Milk solids-nonfat (MSNF):

9% (=12.9-3.9)

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 2. Fluid Milk and Some of Its Derivatives
• Market price of milk is generally based on its fat content and
MSNF content.
• The most important single factor deciding/affecting the
composition of cow milk is the breed of the cow.

• Milk solids further determine the yields of other dairy products

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 2. Fluid Milk and Some of Its Derivatives
2.1 Legal standards

• In many countries, milk is the most legally controlled among all

food commodities.

• Minimum standard for fat: 3.0-3.8%,

total solids: 11.2-12.25%

• Normally, milk is referred to as a human’s most nearly perfect

food from a nutritional standpoint.

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 2. Fluid Milk and Some of Its Derivatives

2.1 Legal Standards (continued)

• Veterinary inspections are regulated on farms and specific

sanitary requirements throughout the entire chain of milk
handling and milk processing.

• It is essential to protect heath because improperly handled milk

can be a source of serious disease
⇒ strict sanitary control and sanitary practices by dairy industry

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 2. Fluid Milk and Some of Its Derivatives

2.2 Milk Production Practices

• Hand milking is a thing of the past.
• Milking machines working on “production automation”
- a vacuum principle squeeze and suck milk from teat canals
into receiving vessels;
- or the milk is drawn under vacuum from the milking machine
cups through pipes leading to a bulk holding tank in another
room.

• This tank is provide with refrigeration to quickly cool the milk to 4.4°C or
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lower to control bacterial growth
 2. Fluid Milk and Some of Its Derivatives
2.2 Milk Production Practices
• Milk in healthy cow’ udder is sterile, but quickly becomes
contaminated with m/o from the external cow’s body and from
milk-handling equipment.
• Milk in the cold tank on the farm is transported to a milk-
receiving station or milk processing plant by bulk tank trucks.

2.3 Quality Control Tests

• On receipt of milk at processing plant, several inspections and
tests may be performed to control the quality of incoming
product (raw milk).
✓ Determination of total fat and total solids by chemical or physical
analyses;
✓ Estimation of sedimentation;
✓ Determination of bacterial counts (total count, coliform count, yeast
and mold count);
✓ Determination of freezing point;
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✓ Evaluation of milk flavor
 2. Fluid Milk and Some of Its Derivatives
2.3 Quality Control Tests (CONTINUED)
• Under special circumstances, tests for detection of antibiotic
residues from treated cows and for pesticide residues also may
be made.

• Guide to the setting of microbiological and sanitary standards:

✓ Grade A raw milk for pasteurization: not exceed a total bacterial
count of 100,000/ml on milk
✓ Grade A pasteurized milk: not exceed a total bacterial count of
20,000/ml on milk or a coliform count of 10/ml on milk.

• Off-flavor on milk
➢ Cows eating unusual feeds
➢ From unclean barns and excessive bacterial multiplication
➢ Action of milk lipase enzyme breaking down fat
➢ By oxidation causing by contact with traces of copper or iron in
valves, pipes or other equipment ⇒ replaced by stainless steel
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 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
• Milk is held cold, preferably at 4.4°C (= 40F).
• Clarification → Pasteurization → Homogenization

① Clarification
• Removal of impurities: Through a centrifugal clarifier to
remove sediment, body cells from udder, and some bacteria.
• These impurities have different density from liquid milk, with a
different distance under the influence of centrifugal force to
be removed from the milk.

• Clarification is NOT intended to rid the milk completely of

bacteria, and the clarifier was not designed for this purpose.

• Clarified milk is ready for pasteurization.

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 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
① Clarification

Centrifugal milk clarifier

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 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
② Pasteurization
• Aim of pasteurizing milk is to rid the milk of any disease-
producing organisms and to reduce substantially the total
bacterial count for improving and keeping quality.

• Also destroys lipase and other natural milk enzymes (e.g.

alkaline phosphatase).

• Pasteurization temperatures and times were selected to ensure

결핵균 destruction of Mycobacterium tuberculosis, the highly heat-
resistant non-spore-forming bacterium, that can transmit
tuberculosis to humans.

• 62°C for 30 min: destruction of Mycobacterium tuberculosis

• 63°C for 30 min: destruction of Coxiella burnetii (causing Q
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폐렴성 열병 fever, pneumonia)
 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
② Pasteurization
• Two accepted methods for milk pasteurization:
(1) Batch (holding) method
- Heating every milk particles to not less than 63°C for not less than
30 min
(2) high-temperature-short-time (HTST) method (continuous type)
- Heating every milk particles to not less than 72°C for not less than
15 sec

• Pasteurized milk is NOT sterile and so it must be quickly cooled

following pasteurization to prevent multiplication of surviving
bacteria.

• Pasteurization at these temperatures dose not produce a

cooked-flavor in milk and no important effect on nutritional
value of milk. 17
 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
② Pasteurization
• Batch pasteurization is carried out with an agitator to ensure
uniform heating

• It needs a cover to
prevent contamination
during the holding
period.

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 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
② Pasteurization “Plate Heat Exchanger”
• HTST pasteurization requires more complex system with
heating plates, holding tube, flow diversion valve, and time-
temperature recording charts.
• Vacuum chamber to the left is to remove
volatile off-flavors from the pasteurized milk

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Typical HTST pasteurization system for milk
 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
② Pasteurization

“Plate Heat Exchanger”

< Pasteurizer >
1) Balance tank
2) Feed pump
3) Flow controller
4) Regenerative preheating sections
5) Centrifugal clarifier
6) Heating section
7) Holding tube
8) Booster pump
9) Hot water heating system
10) Regenerative cooling sections
11) Cooling sections
12) Flow diversion valve 20
13) Control panel
 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
③ Homogenization
• After pasteurization, milk is homogenized.
• The purpose of homogenization is to make more permanent and
uniform suspension of the fat by reducing the fat globules to a very
small diameter, preferably not more than 1µm (0.001 mm).
• Aim of homogenization is to subdivide the fat globules and clumps to
small size
⇒ no longer rise to the top of the milk
• Advantage:
- makes milk more uniform and prevents cream from rising to the top
of container
- Richer taste and whiter color

• Large fat globule (0.1 to 20µm) to one-tenth of original diameter.

• Homogenization and cooling of milk is followed by packaging, and
then delivered in refrigeration to retail.
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 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
③ Homogenization • Accomplished by forcing the liquid
through a very small orifice under
suitable conditions of temperature and
pressure (50°C and 200 ATM, 1st stage
and 50 ATM, 2nd stage are usual).

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 2. Fluid Milk and Some of Its Derivatives
2.4 Milk Processing Sequence
③ Homogenization

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 2. Fluid Milk and Some of Its Derivatives
• Milk is a great source of bone-
2.5 Related Milk Products building calcium and phosphorus.
• Vit D accelerates the absorption of
calcium and phosphorus, helping
1) Vitamin D milk: addition of Vit. D to milk formation of teeth and bones
2) Multivitamin mineral milk
3) Low-sodium milk: for the people with high blood pressure or
edema
4) Soft-curd milk: easier to digest by infants and young children
(infant formula)
5) Low-lactose milk: for people with lactose intolerance, people
with low level of lactase enzyme. Prepared by treating
(hydrolysis) milk with lactase during processing, or adding this
enzyme to regular milk.
6) Sterile milk: Ultrahigh-temperature (UHT) method at 150°C for
2-3 sec, quickly cooled, and aseptically packaged.
7) Evaporated milk: condensed to 2.25 times
8) Sweetened condensed milk
9) Dried whole milk: dehydrated to 97% solid by spraying or 24
vacuum drying.
 2. Fluid Milk and Some of Its
Derivatives
2.6 Separation of Milk
• Milk can be separated into 2 principal fractions:
cream and skim milk
• Separation is made in a centrifugal cream separator.
• Skim milk having a heavier density than whole milk or cream
is driven by centrifugal force to the outside bowl, while the
lighter cream moves toward the center of the bowl.

• Cream is used directly, or frozen, concentrated, dried, or

further separated to produce butter oil and serum solids.

• Low-fat milk:
✓ Skim milk contains 0.5% or less fat
✓ Low-fat milk contains 1% or 2% fat.
✓ Because fat-soluble vitamins are removed when milk fat is
separated, thus skim- or low-fat milk require addition of
vitamin A and D. 25
Vit D helps or accelerates the absorption of bone-building calcium and phosphorus
 2. Fluid Milk and Some of Its Derivatives
2.7 Milk Substitutes
• Butterfat has sold for about 5 times the price of common
vegetable fats and oils.
• Filled milk or Imitation milk: milk substitutes made by combining
nondairy fats and oils with certain milk solids. They contain no
milk fat.

2.8 Growth Hormones and Milk Production

• Increased milk production and growth rate of young animals
• Bovine Growth Hormone (BGH)
• Bovine Somatotropin (BST)
• Numerous scientific studies and several review panels have found
no reason for concern. (without controversy)

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https://www.youtube.com/watch?v=vbTjPbwZyME
 3. Ice Cream and Related Products
• Ice cream was known in England in the early 1700s.
• Annual consumption in U.S.: 1 billion gallons (= 3.8 billion liter) of ice
cream / year
• Korea 2.5, Japan: 6, Europe 25, US 27 liter/person/year
• Market size: about \ 1.6 trillion in Korea
3.1 Composition of Ice Cream
• Ice cream is composed of milk fat and MSNF, plus sugar, stabilizer,
emulsifier, flavoring materials, water, and air.

• Table 13.4: Typical compositions

of commercial ice creams and
related products
• about 12% (w/w) milk fat, 11%
MSNF, 15% sugar, 0.2% stabilizer,
0.2% emulsifier, a trace of vanilla
⇒ about 38.4% (w/w) total solids
and the remainder of water
• Sherbet contains less than 2% fat,
and ices contain no fat. 27
 3. Ice Cream and Related Products
3.1 Composition of Ice Cream

• Milk fat is the most expensive major ingredient of ice cream.

• The higher milk fat content in ice cream, the more expensive the
product.

• Federal standards in U.S.:

no less than 10% fat and 20% total milk solids for plain ice cream
no less than 8% fat and 16% total milk solids for the ice creams with
chocolate, nuts, and fruits

• Products with leaner compositions may not be called “ice cream”, but
standards are subject to further changes because of increasing
demands for lower-fat products.

• Ice cream contains air, and it is truly a whipped product.

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 3. Ice Cream and Related Products
3.1 Composition of Ice Cream
• Air is uniformly whipped into the product as small as cells (air cell), and
these air cells are necessary to prevent ice cream from being too
dense, too hard, and too cold in the mouth.

• Overrun: The increase in volume caused by whipped air into the mixture
during the freezing process is known as overrun.

• Usual range of overrun in ice cream is about 70-100%

(ex) 1 liter of mix makes 2 liters of frozen ice cream with 100% overrun.

(volume of ice cream − volume of mix )

% overrun =  100
volume of mix

• It is very important for ice cream preservation to keep original overrun

during the storage. It affects texture and body of product. 29
 3. Ice Cream and Related Products
3.2 Functions of Ingredients
• Milk fat: contributes rich flavor, smooth texture and body. Source of
calories.

• MSNF: flavor, body, desirable texture. Higher level of MSNF permits

higher overruns without textural breakdown.

• Sugar: sweetness; lowers freezing point; (ex) sucrose from cane or

beet, dextrose from corn syrup, dextrose-fructose mixture.

• Stabilizer:
- It forms gels with the water in the formula and improve body and
texture.
- Stabilizer gives a drier product, which does not melt as rapidly or leak
water.
- Stabilizer by binding water also helps to prevent large ice crystals
during freezing, which would give the product a coarse texture.
- (ex) gelatin, gum guar, gum karaya, seaweed gums, pectin, CMC, etc.
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 3. Ice Cream and Related Products
3.2 Functions of Ingredients
• Emulsifier:
- It helps disperse fat globules throughout ice cream mix.
- Prevents fat globules from clumping together and churning out as
butter granules during the freezing-mixing operation.
- Improves whipping properties to reach desired overrun and further
helps to make ice cream dry and stiff.
- Egg yolk is good natural emulsifier due to its lecithin content.
Commercial emulsifiers contain monoglycerides and diglycerides.

• Flavors:
- Contributes variety and consumer appeal.
- Vanilla, chocolate, strawberry, fruits, nuts, other combinations

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 3. Ice Cream and Related Products
3.3 Manufacturing Procedure

Pasteurization → Homogenization → Ageing the mixture

→ Freezing → Hardening of ice cream

• The first step in preparing ice cream mix is to combine liquid

ingredients in a mixing vat and bring them to 43°C.

• Next, sugar and dry ingredients are added to the warm mix to dissolve
them.

• Nuts or fruits are added to the mixture during the freezing step.

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 3. Ice Cream and Related Products
3.3 Manufacturing Procedure

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 3. Ice Cream and Related Products
3.3 Manufacturing Procedure
(1) Pasteurization:
- By batch or continuous (HTST) heating process
- Pasteurization temperature for ice cream mixture is higher than for
plain milk because high fat and sugar contents tend to protect
bacteria from heating destruction.
- 71°C for 30 min: batch process
82°C for 25 min: continuous (HTST) process
- Pasteurization equipment is same as that used for milk

(2) Homogenization:
- Normally by two-stage homogenizer
- Breaks up fat globules and clumps
- Improves overall body and texture of ice cream
- After homogenization, mix is cooled to 4.4°C
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 3. Ice Cream and Related Products
3.3 Manufacturing Procedure
(3) Ageing the mix:
- The mix is held from 3 to 24 h at 4.4°C or lower in vats.  ageing
- During ageing stage,
✓ the melted fat solidifies
✓ Gelatin or other stabilizers swells and combines with water
✓ Milk proteins swell with water
✓ Thus, viscosity of mix increases
- These changes lead to quicker whipping to desired overrun in the
freezer, smooth ice cream body and texture, and slower melt-
down.
(4) Freezing:
- By batch or continuous freezer
- Ice cream mix and air enter the freezing cylinders and they are chilled.
- Main purpose: This operation is to freeze the mix to about -5.5°C and to
beat in and subdivide air cells. 38
 3. Ice Cream and Related Products
3.3 Manufacturing Procedure
(4) Freezing (continued):
- There are (1) rotating blades inside the barrel that keep the ice
scraped off the surface of the freezer and also (2) dashers inside
the machine which help to whip the mix and incorporate air.
- Freezing must be quick to prevent growth of large ice crystals, and
coarsen texture.
- Air cells must be small and evenly distributed for stable frozen foam.

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 3. Ice Cream and Related Products
3.3 Manufacturing Procedure
(4) Hardening of ice cream:
- After packaging, semisolid ice cream is placed in a hardening room at -34°C
- Storage in hardening room freezes most of remaining water and
makes ice cream stiff.
- When products are stiff, they are ready for sale.

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 3. Ice Cream and Related Products
3.4 Physical Structure of Ice Cream
• Ice cream is a foam containing air cells.
• In ice cream foam, the films of mix surround the air cells.
• Fat globules are dispersed within the films or layers of mix.
• Also, frozen ice crystals are within the films.
• As ice cream ages in storage, the foams can shrink. In addition, weakened
films of mix can collapse, causing ice cream to lose volume.  defect!

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Three-phase dairy foam system Ice cream air cells: (a) air cell, (b) ice crystals
 4. Cheese
Milk proteins:
- Casein: αS1-casein, αS2-casein, β-casein, κ-casein
- Whey proteins: β-lactoglobulin, α-lactalbumin
• Cheese is another form of milk product to preserve or store it using a
fermentation treatment/technique.

• Cheese is a high quality/value and nutritional gourmet food

- Needs around 10 kg of raw milk to produce 1 kg of cheese

• Cheese is a food consisting of proteins and fat from milk, usually the milk
of cows, buffalo, goats, or sheep.

• It is produced by coagulation of the milk protein casein. Typically, the

milk is acidified and addition of the enzyme rennet causes coagulation.

• The solids are then separated and pressed into final form.

• Hundreds of type of cheese are produced. Their different styles, textures

and flavors depend on the origin of the milk (including the animal's diet),
whether it has been pasteurized, butterfat content, the species of bacteria
and mold, and the processing including the length of aging. 42
 4. Cheese
• Fermentation in cheese-making:

Propionibacterium

lactose → lactic acid → propionic acid + CO2

Lactic acid bacteria:
Lactobacillus sp. or Streptococcus lactis

• Proteolysis during cheese Manufacture and Ripening:

milk proteins (casein) are hydrolyzed by proteolytic m/o or enzymes

Table 13.5: Classification of cheese based

on textural properties and kind of ripening

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4. Cheese

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 4. Cheese
brick

cream

brie

gorgonzola

camembert

parmesan

cheddar

Gorgonzola:
- starter bacteria is added, along with spores of the mold Penicillium
swiss
glaucum. Penicillium roqueforti
- During the aging process metal rods are quickly inserted and removed,
cottage creating air channels that allow the mold spores to grow into hyphae
and cause the cheese's characteristic veining. 45
 5. Reduced Fat Dairy Products
• It has been a desire to reduce calories, saturated fat and cholesterol in
dairy products.

• reduced-fat and low-fat dairy-like products have appeared. (imitations or

analogues)

• Substitute nonfat food ingredients for animal fat in dairy product. (ex.
Low-fat ice cream)

• Fat replacers:
✓ designed to replace functional characteristics of fat, such as texture,
mouthfeel.
✓ made of proteins or carbohydrates-based replace

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 Homework due by ???

(1) Please describe about “ fat replacers” in detail.

(2) Please explain about Olestra including its

chemical structure, significance, nutritional values,
safety, industrial applications, merits, pros and cons,
etc.

(3) Provide any other newly developed fat replacers.

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