Milk has five nutrients: protein, fat, carbohydrates, vitamins, and inorganic salts.

Milk contains about 3.5% protein (human milk is about 1.25%), of which casein is the main one, followed by milk white eggs and lactoglobulin. They all contain all of the body's essential amino acids, and their relative content is similar to that of egg proteins, with a higher digestibility of 96.1%.

Casein accounts for about 86% of the total protein, lactalbumin accounts for about 9% of the total protein, lactoglobulin accounts for about 3% of the total protein, and other serum white, immunoglobulin and enzymes.

Identification of fresh milk:

Fresh milk is a milky white or yellowish uniform gelatinous fluid, no precipitation, no clots, no impurities, no viscous, no odor.

Fresh milk contains sugars and volatile fatty acids, which gives it a slightly sweet and clean milky flavor. Pour the milk into a glass and shake it, the milk will hang easily on the wall. A drop of milk on the glass, the droplets are rounded and not easy to disperse. There is no condensation or flocculation when boiling.

If the milk is thin, whitish, the flavor is reduced, not easy to hang wall; or drop on the glass, the milk drop is not shaped, easy to disperse, it is watered milk.

If you boil it and then cool it a little, the surface appears tofu flower-like curd or flocculent, indicating that the milk is not fresh or has been spoiled.