Have you seen "rennet" listed as an ingredient on the package of your favorite cheese. I thought there were different forms of rennet, but wasn't exactly sure, so I did some research.
Rennet is a natural complex of enzymes produced in the stomach of mammals to help digest it's mother's milk. Inside the young animal's stomach, the rennet coagulates the milk, causing it to separate into curds and whey.
In the cheese-making process, rennet is added to the ingredients to do the same thing. The curds are separated from the liquid (whey), and it's then processed and matured to produce a wide variety of cheeses.
The rennet you find in cheese can come from 3 sources: the stomachs of calves (it's extracted after they are killed for veal), from plants, or from microbes (molds or fungus).
The word "enzymes" may also be listed in the ingredients instead of "rennet." Cabot cheese does this and when I called, I found out they use microbial enzymes (not from animals).
Fit's Tips: Just because "rennet" is listed in the ingredients, does NOT mean it comes from calves. Likewise, just because it says "enzymes," does NOT mean it comes from plants or microbes. If you are concerned with the type of enzymes found in your cheese, it's best to call the company to find out the source.