The Biochemistry of Milk
Ch. 23

How do you milk a cow?
Video
 http://www.moomilk.com/faq.htm#To
%20make

The Complex Nature of Milk
Milk supplies the calcium for building
bones and teeth, especially during
adolescence
 Milk is 87% water

 However
that’s a solvent for over 250 chemical
compounds, milk sugar (what is the name for
milk sugar_____?____) water-soluble vitamins
and trace minerals and salts
Protein


Two main proteins make up milk:
 80%
Casein = milk protein
 20%
Whey = milk protein
Micelles = an aggregation or cluster,
of molecules, often found in colloidal
dispersions

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The light reflecting from micelles makes milk white
As long as milk keeps its normal acidity
level, about pH 6.6, casein remains
stable
Protein Continued
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When the pH level decreases the milk forms
lumps or coagulates.
Curds = The casein clumps that separate
from the liquid when milk coagulates

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When cooking with milk you can prevent curdling by using
starch to thicken the milk
If you want to coagulate milk, you can use the enzyme
rennin or vinegar.
Whey = protein found in the liquid that
remains after fat and casein have been
removed from milk.

Whey is also called serum protein
Fats


Milk is an emulsion because small globules of
fat (lipid) are dispersed throughout the water
Creaming = process in which some of the
fat droplets come together in larger clusters
that rise and float to the top of the milk


These clusters rise to the surface because fat is less dense
than the watery portion of milk
Cream = simply milk that is extra rich in
emulsified fat droplets

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The fat in cow’s milk are most complex lipids, over 400
different fatty acids
Click For Milk Experiment
Carbohydrate

Lactose or milk sugar is the main
carbohydrate


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Lactose provides food energy
Also adds body to milk as well as a sweet flavor
When milk is heated, lactose reacts with amino acids
in the protein (giving cooked milk a slightly caramel
flavor)
When you consume milk, lactose becomes available
to the body because of the enzyme lactase.
 This enzyme breaks lactose down into galactose
and glucose, which is used in the body for
fermentation during digestion.
Carbohydrate Continued

Do you know someone who cannot
drink milk???
can be lactose intolerance = the
inability to digest milk due to the absence of
the enzyme lactase in the intestines
 People

People who are lactose intolerant cannot break
down lactose in their body. When they drink the
milk they can have bloating, stomach cramps and
diarrhea.!!! -NOT FUN
Minerals and Vitamins

Milk has salt that occurs naturally
 Salts
in milk include chlorides and phosphates
(in very low amounts)
 Salt in milk helps prevent curdling
 If an acid is added to milk (what would be an
example of an acid), the pH lowers which
removes the calcium ions from the casein,
making the milk curdle – forming _____and
_______
 Four vitamins found naturally in milk, riboflavin
is found in the largest quantity.

Breaks down when exposed to light
Pasteurization

Shelf Life = time a food product can
be stored before deteriorating.
 When pasteurizing milk, its heated to
high temperatures for a short time to
destroy harmful bacteria
 Pasteurization
denatures enzymes that cause
milk to spoil
 Pasteurization has a small effect on milk’s
nutritional value, creating a slight loss of
thiamin, vitamin B12, vitamin C
 DO YOU THIN THAT DRINKING
UNPASTURIZED MILK IS BETTER FOR YOU?
Homogenization

Under pressure of 2,000 to 2,500
pounds per square inch, milk is forced
through small openings in a machine
called a homogenizer
 The
fat particles break down, an emulsifier
surrounds the fat particle, which keeps the
particles permanently separated

As a result the milk you buy does not have cream on
the top.
Fortification

Fortification = the addition of a
nutrient to a food
 Ex.

What nutrient is milk fortified with___?___
Without vitamin D, your body can’t absorb calcium
and phosphorus very well.
 To fortify milk with vitamin D, it may be exposed
to ultraviolet light, which convert some of the
milk fat components to vitamin d
Fluid Milk/ UltrahighTemperature Milk (UHT)

Fluid milk is categorized by fat content
 Whole
milk – 8g fat
 Reduce-fat milk (2%) – 5g fat
 Low-fat milk (1%) - 2.5g fat
 Fat-free milk – trace fat

Ultrahigh-Temperature Milk (UHT)
 With
special processing milk can be stored
without refrigeration for three months

This is called UHT because it’s prepared by heating
for a short time at ultrahigh temperatures.
 Placed in special sealed packages
 Flavor improves over time
Concentrated Milk

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Evaporated milk – is whole milk that has
been heated at low pressures, causing up to
60% if the water present to evaporate at
temperatures well below milks normal boiling
point.
Carrageenin = a vegetable gum, is often
added to evaporated milk before processing
to stabilize the casein proteins
Sweetened condensed milk – canned product
in which 50% of the water has been
removed and sugar added.

Sweetened condensed milk is 44% sugar
Cream/Dry Milk

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Half-and-half = is 10.5-18% fat
Light cream = 18-30% fat
Light whipping cream = 30-36% fat
Heavy whipping cream = contains at least
36% fat
Dry Milk – water is removed, leaving a dry
solid material

Milk Solids = proteins, carbohydrates, fat,
minerals, and vitamins that were dissolved in the
liquid portion of the milk

Nonfat milk has a longer shelf life because it has the least
amount of fat (used for baking an enriching products)
Cultured Milk Products

Culture = controlled bacterial population that is
added to milk

The starter bacteria produce acid and flavors that are
characteristic of each fermented milk product.


Commercial producers use lactic-acid bacteria to break down
lactose
Inoculation = adding the starter culture to milk
during the fermentation process that produces
different cultured milk products
 Incubation period = time needed for bacteria to
grow and ferment the milk during the process of
culturing milk to make various products – finally it’s
cooled down to stop or slow bacterial growth
What are some examples of cultured foods???
Buttermilk/Sour Cream/Yogurt


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Buttermilk – used to be the fluid left over
from producing butter, today it’s a cultured
product prepared from low-fat milk
Sour Cream – culture of streptococcus lactis
is added to cream.
Yogurt – eastern European food, yogurt
contains lactose, lactic acid, B vitamins and
high concentrations of protein

Yogurt is prepared by adding a bacterial culture to milk
that has been heated

Bacteria used to making yogurt must be incubated
between 41°C-45°C for around 8 hours
Cheese

Cheese is made by coagulating the casein
protein in milk.

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Once the curds have formed, the whey is drained
away. (heating and cutting the whey helps this drain)
The curd is then treated and allowed to ripen

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During ripening, the cheese is hung for at least 60 days,
some take months
Four main categories of cheese are based on moisture
content:
Very hard cheese – parmesan and Romano
2. Hard cheese – cheddar, Colby and provolone
3. Semi-Soft cheese – Munster, Roquefort, and stilton
4. Soft cheese – brie, camembert, and mozzarella
Unripened Cheese – cottage cheese and cream cheese
1.
Storing and Cooking with Milk

How many of you leave milk on your table
when eating dinner??
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Milk retains it’s quality for 1-3 weeks when
properly stored
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Is that safe?? – Even if it’s for ½ hour?
Extra credit for someone who can tell me the correct
temperature
Remember riboflavin is sensitive to light
Would whole milk or low fat milk spoil faster
or would they spoil at the same time?
Making Foams

Several factors affect the ability of cream to
make a foam.

Fat content – higher the fat level, the better the

Temperature – cold temperature increase the
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foam
viscosity , including the beaters and bowl
Amount of cream – whipping small amounts of
cream usually gives better results than whipping
large amounts
Sugar content – adding sugar decreases both the
volume and stiffness of the foam, its best to add
sugar after the cream has reached the desired
consistency
Heating Milk

Milk is sensitive and highly reactive to
heat

Heat denatures and coagulates the whey
proteins of fresh milk, causing them to
precipitate
 Precipitate
= to cause a solid substance to
separate from a solution


To prevent milk from scorching put milk in a double
boiler or heat over VERY LOW TEMPERATURE
What happens to milk when you heat milk in a sauce
pan that is not stirred?!??
 Skin develops, if you try to remove the skin it
will regenerate and you lose milk solids
 What is curdling and how does it happen
Questions
1.
2.
3.
4.
5.
6.
How does casein react to acids?
How are casein and why alike and
different?
What makes milk a solution, a colloidal
dispersion, and an emulsion?
Why is lactose a valuable nutrient in milk?
How do salts prevent milk from curdling?
How is milk processed? What is the
purpose of each type of processing?
Questions Continued
7.
8.
9.
10.
11.
12.
What does the phrase “whole milk” mean? How
does whole milk compare to other classifications of
milk?
What is the difference between sweetened
condensed milk and evaporated milk?
How are cultured milk products made?
Explain what ripening is and why it’s needed to
make cheese.
To make a cream foam, would you get better
results by using light or heavy whipping cream?
WHY?
What might happen if you leave an open pan of
milk over high heat without stirring?