For centuries cheesemakers have used animal rennet, which is comprised primarily of the enzyme rennin (also called chymosinrennet) and obtained from the gastric juice found in the fourth stomach (abomasum) of young ruminants. This coagulating enzyme is used to curdle milk in foods such as cheese and junket. But today there are other "rennet" choices, in part due to the widely fluctuating price of animal rennet and also because animal products are a problem for some Jews and vegetarians. Vegetable-based coagulants are substances organically extracted from a variety of plants including thistles, nettles, fig leaves and safflowers. They have a coagulating effect almost as powerful as their animal-derived counterparts. are produced by introducing the animal's rennin-encoding DNA into a yeast or bacteria micro-organism, which can then be cultured to create rennin. Alternatively, bio-synthesis can be used to do the same thing without the use of animal cells. Microbial enzyme coagulants are made from the fermentation of fungi or bacteria. They act like rennet and are relatively inexpensive. Rennin is available in most supermarkets in tablet or powdered form. Other types of coagulants can often be found through suppliers of cheesemaking paraphernalia.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.