Vegetarians should note that most cheese is not vegetarian, as it contains animal rennet, which, as Webster points out, is part of a cow. Rennet is used to speed up the coagulation of milk. There are some companies, such as Cabot, that produce cheese using either no rennet or an artificial rennet. The artificial rennet, sometimes known as "vegetable rennet" is actually produced by bacteria modified with recombinant DNA.

You can tell whether or not a cheese contains animal rennet: if the list of ingredients contains the word "enzymes," it uses animal rennet, unless it specifically states otherwise. For example, many cheeses produced by Cabot specifically state, "Contains no animal rennet."