As the pH is lowered, the structural nature of the proteins also change. The casein proteins that form the curds entraps water and fat. The most common method being used for coagulation is by the addition of enzymes. The physical properties of enzyme coagulated cheese are superior to the acid coagulated cheese. The most common source is rennet.
Rennet is made from the lining of the fourth stomach of calves.
Microbes play an important role in determining the type of cheese that is made. When milk is coagulated it will separate into curds and whey. The curd is solid and the whey is liquid. The casein helps in coagulating the milk. The albumin is in the whey.