Complex Nature of Milk • Milk is a solution, an emulsion, and a colloidal dispersion • Normal pH of milk is about 6.6 • 80% water
Composition of Milk • Casein makes up most of milk - When pH is lowered to 4.6, casein breaks down, coagulates, and turns to curds - heat has little effect on coagulating casein
Whey makes up 20% of milk - also called serum protein - heat easily coagulates whey
Fat - milk is an emulsion - Micelles are clusters of molecules that occur within the colloidal dispersion - Globules vary in size and have a thin membrane around them - Milk fat contains very little cholesterol
- Fats influence flavor, texture, and price - More fat usually equates to more costly milk
Minerals & Vitamins - calcium, potassium, magnesium, sodium, thiamin, niacin, vitamin A, riboflavin - one function is to prevent curdling - riboflavin breaks down when exposed to light
Carbohydrate - Lactose (milk sugar) • When milk is heated, reacts with amino acids in protein to produce Maillard reaction, turns a golden brown color and slightly caramel flavor
Lactose Intolerance - inability to digest milk due to the absence of the enzyme lactase in intestines
Processing of Milk • Pasteurization – heating raw milk to high temps to destroy bacteria, then cooled. • Homogenization – breaking up milk fat into smaller globules which disperses them permanently, eliminates creaming • Fortification – adding Vitamin D and Vitamin A
Types of Milk • Raw - unpasteurized milk straight from the cow • Whole – Contains not less than 3.25 % milk fat. Also fortified with vitamin D. • Low-fat milk – milk fat removed to bring the levels between 0.5-2%. Vitamin A is added.
Skim milk – milk fat removed to bring the level to less than 0.5%. Fortified with Vitamin A. • Ultra High Temperature– allows milk to be stored without refrigeration for 3 months or more if unopened
Concentrated - Evaporated milk: canned whole milk concentrate with 60% of water removed - Sweetened condensed milk: 50% of water is evaporated and sugar is added
Cream - Whipping cream is the fat from whole milk • Nonfat dry milk: milk dried to powdered form.
Cultured milk products - Sour cream: cream that has been soured by lactic-acid bacteria
- Yogurt: made by fermenting skimmed milk with special acid-forming bacteria
Storage of Milk • Closed container protects flavor • Opaque container protects riboflavin • Canned milk: cool, dry place • Dry milk: cool dry place • Freezing milk changes consistency