Casein, << KAY seen or KAY see ihn, >> is the chief protein in milk. It is also the main ingredient in cheese. Casein separates as curd when milk sours, or when acid is added. It also separates from sweet milk when the enzyme rennin is added. Casein contains carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Pure casein is a tasteless, odorless, white solid. Cow milk contains about 3 per cent casein. See Cheese ; Milk .
Casein is produced commercially from skim milk. The curd is washed, dried, and ground. Commercially prepared casein is pale yellow and has a pleasant odor. It is widely used in medicines, cosmetics, and as a sizing (coating) for paper. Casein is also used in waterproof glues, casein paints, and certain plastic articles such as buttons.
