The Complex Nature of Milk
 Vital to health - nutritious
 Versatile for cooking – 87% water (a solvent for over
250 chemical compounds, the milk sugar lactose,
water-soluble vitamins, trace minerals and mineral
salts)
 Milk is a solution, a colloidal dispersion, and an
emulsion
World use of milk
 Around the world, people use milk from many
different kinds of animals, but cow’s milk is the most
common type consumed.
 Milk contains all major nutrients: water, protein,
carbohydrates, vitamins and minerals…
 The exact composition depends on the cow’s breed,
health and environment.
Proteins
 80% of milk protein is casein
 Casein molecules associate with each other in tiny,
raspberry-like structures called micelles – an
aggregation, or cluster of molecules often found in
colloidal dispersions
 As long as milk keeps its normal acidity, level
(pH - 6.6), casein remains stable…if an acid is added, the
casein coagulates to form curds. When cooking, you
can prevent curdling by using starch to thicken the
milk. The starch surrounds the casein and prevents
coagulation.
Proteins
 20% of milk protein is whey
 Whey is the protein found in the liquid that remains
after fat and casein have been removed from milk
 Whey is also called serum protein. Heat will easily
coagulate whey, although heat has little effect on
coagulating casein.
Proteins
 In addition to the proteins, casein and whey, milk
contains a number of enzymes that are also protein
molecules. Most of these are denatured during
pasteurization.
 Another way to coagulate milk is with the enzyme
rennin, which is used to clot milk in the first stage of
cheese making.
Fats
 Milk is an emulsion because small globules of fat are
dispersed throughout the water. Around each fat
globule is a thin membrane containing proteins,
phospholipids and bound water, suspending clusters
of fat in droplets.
 Creaming – fat droplets form larger clusters that rise
and float to the top.
 Cream is milk that is extra rich in emulsified fat
droplets
Fats
 The fats in cow’s milk are the most complex lipids
known. The lipids include over 400 different fatty
acids.
 Milk fat contains very little cholesterol compared to
egg yolk.
 The fats in milk influence the flavor, texture and price
– the more fat, the higher the price.
Carbohydrate
 Milk sugar – Lactose
 Lactase – enzyme that breaks lactose into glucose and
galactose
 Lactose intolerance – no lactase in intestines – lactose
remains undigested, then certain intestinal bacteria
attack and ferment the lactose, producing acids and
gas – this causes discomfort
 Cultured milk products (yogurt, buttermilk)
Vitamins and Minerals
 Minerals – in the form of salts – chlorides, phosphates,
citrates of potassium, calcium, sodium, and
magnesium (salts prevent milk from curdling)
 Trace elements – cobalt, copper, iodine, iron,
magnesium, nickel, molybdenum
 Vitamins:
 Riboflavin – breaks down when exposed to light – this
is why milk cartons are opaque
 Thiamin
 Niacin
 Vitamin A
Processing Milk
 Pasteurization – heated to a high temperature for a
short time – destroys pathogenic bacteria
 Homogenization – eliminates creaming – under
pressure, milk is forced through small openings to
break down fat and keep the fat molecules
permanently separated
 Fortification – Vitamin D is added (helps the body
absorb calcium and phosphorus), and Vitamin A (a
fat-soluble vitamin) is added back to low-fat milk
products (by law)
Types of Milk Products
 Fluid milk
 Ultrahigh-Temperature Milk (UHT) – in sealed box
– long shelf-life (3 months or more if unopened)
 Concentrated milk – Evaporated – carrageenin is
added to stabilize the casein – off white color is caused
by chemical reaction of lactose and amino acids
 Sweetened condensed – 50% of water is removed,
44% sugar is added – used in dessert recipes
Types of Milk Products
 Cream
 Half and Half – 10.5% to 18% fat
 Light cream or Coffee cream – 18% to 30% fat
 Light whipping cream – 30% to 36% fat
 Heavy whipping cream – at least 36% fat
 Whipping cream is often UHT pasteurized to lengthen
shelf life
Types of Milk Products
 Dry milk – dried into powder form – milk solids can
be reconstituted by adding water
 Non-fat dry milk has longer shelf life – no fat to
oxidize and spoil the product
 Cultured milk products
 Fermented – buttermilk, yogurt, cheese
 Process – pasteurized, lactic-acid bacteria breaks down
lactose (lowers the pH), inoculation (starter is added),
incubation, cooling
Cheese
 Made by coagulating the casein protein
 Ripening – aged – makes the flavor and texture
distinct
 Moisture content varies
 Very hard – Parmesan, Romano
 Hard – Cheddar, Colby, provolone
 Semisoft – Muenster, Roquefort
 Soft – Brie, Camembert, mozzarella
 Unripened – cottage cheese, cream cheese, mozzarella
Storing Milk Products
 Keep it COLD!!
 Use closed, opaque containers – riboflavin is light-
sensitive
 Refrigerate cans or UHT boxes after opening
 Store non-fat dry milk at room temperature – keep
moisture out
 Keep cheese cold, although it tastes better when
served at room temperature – wrap carefully to keep it
from drying out
Cooking with Milk
 Making foams
 More fat = higher viscosity (thickness) = better whipped
cream
 Cold temperatures increase viscosity – whip cream when
it’s cold!! Use cold mixing bowls and beaters
 Whip small amounts
 Adding sugar decreases the volume and stiffness of the
foam, so add sugar after whipping the desired amount of
air into the foam
Cooking with Milk
 Heating Milk
 Milk scorches – it’s highly sensitive and highly reactive
to heat – heat denatures and coagulates the whey
proteins of fresh milk, causing them to precipitate, then
it settles to the bottom, and scorches – use a DOUBLE
BOILER to prevent this
 When heated till scalding in open containers,
evaporation causes a skin to form on top (marshmallow
or whipped cream prevents this)
 Curdling can occur at high temperatures – use low
temperatures and non-acid ingredients to prevent this
Cooking with Milk
 Enzyme action
 Some desserts use rennet to make clotted milk - use
moderate temperatures so enzyme is not inactivated
 Acids
 Causes milk to curdle (like when you add fruit to your
milk and cereal or lemon juice to tea and milk)