Both vegetable rennet and animal rennet are used to make cheese, and they are both available in different forms, such as liquid, tablets, or powder. Rennet is used in the cheese making process to help speed up the thickening, or coagulation, of the milk proteins in order to separate the cheese curds from the whey. The whey is poured off and the curds are then cooked, and sometimes they are aged or further processed to make cheeses like Cheddar, Swiss and Mozzarella.
Animal rennet comes from an enzyme called chymosin that is naturally produced in the stomach of a baby cow, goat, or sheep before the animal has eaten anything besides its mother’s milk. When the young animal is slaughtered, the rennet is extracted from its stomach, and then the rennet is processed with milk to produce cheese curds. Adult animals do not have the enzyme, as it is not produced once an animal eats grass, grain, or anything besides mother’s milk. Most European cheese makers use animal rennet to make their cheeses, such as certain Cheddars, Brie, and Mozzarella. Many traditional European cheese makers also store milk in a sort of pouch made from the stomach as well.
Many plants are coagulants and can be used instead of animal rennet to make cheeses. Fig extract is one such plant, and others include thistle, nettles, mallow, and dried caper leaves. Essentially, the plants are just boiled in water, and then the liquid is strained off and stored to use for cheese making. The process for using the vegetable rennet is the same as for animal rennet; the milk is combined with a small amount of acid to begin the coagulation process, and as it is cooking, the vegetable rennet is added to the milk so that cheese curds will form. Some cheeses, like Mozzarella, are ready to be eaten soon after the curds are separated from the whey, while others, such as Cheddar, undergo further processing.
Should You Avoid Either?
Both animal and vegetable rennet are capable of producing delicious cheeses. Avoiding eating cheeses made with one or the other is simply a matter of preference. Many fine European cheeses are made exclusively from animal rennet, such as Parmigiano-Reggiano. Similar cheeses made from vegetable rennet are often considered inferior. On the other hand, many people are bothered by the idea of eating cheese that results from the slaughter of an un-weaned animal, so they choose cheeses that are made from vegetable rennet instead.
Cheese curd produced from animal rennet is not kosher either, so that is another fact to take into consideration. In fact, most kosher cheeses are made from rennet that is produced in a laboratory using microbes. Certain types of fungi, yeasts and microbes have been combined with animal genes so that they will produce chymosin, which is then used to produce cheese curds in the cheese making process. Laboratory produced rennet is generally thought to produce cheeses, such as mozzarella and cheddar, that have a taste and texture very similar to those produced from animal rennet.