By the rennet ferment caseinogen is converted into casein, a substance resembling caseinogen in being soluble in water, but differing in having an insoluble calcium salt.
The formation of casein involves the curdling of milk.
'In chemical constitution it consists of an emulsion of fatty globules (cream) in a watery alkaline solution of casein, and a variety of sugar, peculiar to milk, called lactose.
The casein, which forms the principal constituent of cheese, and a certain proportion of albumen which is present, form the nitrogenous, while the complex saline substances and water are the mineral constituents.
Triferrin is a paranucleinate of iron, and contains 22% of iron and 21% of organically combined phosphorus, prepared from the casein of cow's milk.