Enzymes in Milk

Milk also coagulates and forms curds when it combined with certain enzymes originating from animal, plant, or microbial sources. Enzymes used to coagulate milk include pepsin from the stomach of swine, proteases from fungal sources, and certain enzymes from fruits. The enzyme most commonly used to coagulate milk is rennin, which is used in the production of cheese and ice cream.

One of the major differences between coagulation caused by enzymes and that initiated with acid is that rennin-coagulated clots are rich in calcium and have a tough, rubbery texture, unlike those created by acid, which are less elastic and more fragile in consistency. Cottage cheese, which is normally coagulated by acid, contains less calcium per ounce (19 mg) than cheddar cheese (204 mg), which is usually made with rennin.