Milk germ-free is the need, but to be made sterile (germ-free) would require a degree of heat which changes its composition and digestibility unfavorably. Pasteurized milk and certified milk, as noted, are safer than ordinary raw milk. Other means to this end change the form of milk somewhat.

Milk-powder is mainly milk-curd dried and powdered; it is mixed with water as used. Evaporated milk is skim-milk with the water evaporated; it contains the solids of skim-milk. Its principal use is that of being mixed with special prepared flours. Condensed milk has had most of the water evaporated, high heat applied to destroy bacteria, and sugar added. Sugar acts as a preservative, but it renders such milk unfit for use for all purposes milk usually serves. All these forms of pre-served milk may become re-infected with bacteria after they are opened for use. Koumiss is fermented milk that is of such digestibility as to be a valuable adult invalid food:

Color of milk is not essentially indicative of quality. Light-colored milk may be superior to rich-looking milk, as the latter may be artificially colored; but very pale, thin milk, even if not watered, is poor. Sediment in milk indicates adulteration or lack of cleanliness.

Milk that shows neglect or adulteration should be referred to the Board of Health or Milk Inspector or Commission.

Butter as well as milk and cream needs to be fresh and pure. Pure butter boils quietly when heated in a spoon; impure does not.

Milk furnishes principally protein and fat. The sugar and mineral salts are far from unimportant, but would not in themselves give milk the significance it has as a food. The separated fat gives cream and butter; the separated protein with some fat and salts gives cheese.