1. The Biochemistry of Milk

2. 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

3. 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.

4. 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.

5. 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.

6. 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.

7. 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

8. 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.

9. 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)

10. 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

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. Cooking with Milk Enzyme action Acids
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)