Skimmed buttermilk is to remove part of the normal milk fat, so that the fat content of buttermilk down to less than 0.5%, this value is less than one-seventh of the amount of fat in ordinary milk, here skimmed milk is relative to the whole milk, between the two there is also low-fat milk. The fat content of whole milk is about 3%, low-fat milk (semi-skimmed milk) contains 1.0 to 1.5% fat, and full skimmed milk contains ≤0.5% fat. For modern people, people not only rely on milk to supply energy, often favor the high quality protein contained in milk, so prefer low-fat milk with less fat, become skimmed milk.

Milk

is one of the oldest natural beverages, known as white blood. Milk is rich in protein, fat, vitamins and minerals and other nutrients, milk protein contains essential amino acids; milk fat is mostly short-chain and medium-chain fatty acids, very easy to be absorbed by the body; potassium, phosphorus, calcium and other minerals in a reasonable proportion, easy to be absorbed by the body. Fresh milk is mainly composed of water, fat, protein, lactose, minerals, vitamins and other components of a complex latex, of which the water content accounts for 86% to 90%, so its nutrient content is relatively low compared with other foods. The specific gravity of cow's milk is 1.032 on average, and the size of specific gravity is related to the content of solids in milk. The various components of milk in addition to the relatively large changes in fat content, other components are basically stable, so the specific gravity can be used as a simple indicator to assess the quality of fresh milk.