Fresh whole milk is skimmed and pasteurized before undergoing an acidification at pH 4.6 (isoelectric point of casein). Then the caseins aggregate to form an acid coagulum of casein, commonly called curd. It is separated by a centrifugation of the whey and then washed to obtain a casein containing less than 1% fat, less than 1% minerals and about 0.1% lactose. This curd, insoluble in water, is then ground and dried in dryer. Then the acid casein is obtained.
The rennet casein is a phosphorus-protein complex (micelles) resulting from the milk coagulation by the action of enzymes (chymosin and pepsin) contained in the calf’s abomasum. The micellar structure and the presence of calcium give the rennet casein its texturizing properties. It is mainly used in the manufacture of processed cheese and similar cheeses to which it gives a filata characteristic and good melting properties.