RennetWhen cheese lovers buy cheese, they passionately question the type of milk, the region where the cheese was made, etc. But few (except those looking for vegetarian rennet) if any ever ask about the rennet used to make the cheese. But as more caseophiles understand rennet's importance and origins, they are asking more questions.
Coagulants Used In CheesemakingA coagulant is anything that curdles milk. Rennet is a generic term used to describe an animal-derived coagulant; it includes the enzyme rennin or chymosin.
Animal-Derived RennetMade from a collection of enzymes from the fourth stomach of ruminant animals (kid, calf, or lamb), this is used in most traditional cheesemaking plants. Some perceive the use of animal stomachs to produce rennet naturally as somewhat primitive, others as an example of how we make use of all parts of an animal.
Microbial RennetMicrobial rennet describes a coagulating agent produced by a specific type of mold, fungus, or yeast organism, grown and fermented in a lab. This is considered vegetarian-friendly, as the enzyme produced is not derived from an animal. While this type of rennet is appropriate for vegetarians, cheesemakers agree that cheeses made with this type of rennet tend to result in bitterness in the flavor profile, especially when cheese is aged. While cheaper than animal rennet, true microbial rennet is now hard to find. It has been replaced by FPC rennet.
FPC: Fermentation-Produced Chymosin RennetMade by taking the rennin-producing gene out of the animal cell's DNA string and then inserting into the bacteria, yeast, or mold host cell's DNA string, this type of microbial rennet was introduced in 1990. Once inserted, the newly placed gene initiates the production of the chymosin enzyme within the host. This is cultivated and fermented. The result is an inexpensive harvest of real chymosin. This is seen as an improvement on the original microbial rennet as it is real chymosin and not a mold or yeast-based substitute. Moreover, it can be economically produced in unlimited supply and addresses some of the concerns regarding the bitterness in aged cheeses. The procedure is not new and is similar to that used to make many vaccines. But, there is more to consider.
FPC rennet is a genetically modified organism (GMO). According to the culture companies, 90% of North American cheese is made with FPC rennet. But ingredient labels do not distinguish between this type of microbial rennet and the original non-GMO type. And the fact that use of FPC-type microbial rennet is not labeled a GMO leaves those who oppose GMOs in the dark when it comes to choosing cheese.
In addition, further confusion and debate arises over the differences between GMO products versus genetically engineered products as the latter elicits deeper concerns from those opposed to this type of science. While FPC rennet is GMO, it is not, technically speaking, genetically engineered, because the DNA taken from the animal cell and inserted into the DNA string of bacterium or mold is not changed. Genetic engineering actually modifies the specific gene responsible for a particular function in order to improve its action. In other words, it takes messing with genes to another, deeper level, like playing with the shape of the Lego block itself, not just with the order of their assembly.
In the end, what this means is that most cheese in North America is made from vegetarian-friendly but animal-origin, GMO-derived FPC rennet.
Vegetable RennetTrue vegetable rennet (vs. vegetarian rennet - a term used interchangeably with microbial rennet) comes from plants which produce enzymes that have coagulating properties. Examples include: cardoon thistle, fig tree bark, or nettles. These are real vegetable rennet, though they often also have undesirable effects on cheese flavor (bitterness) and are a little more unpredictable when used in some cheese.
Citric Acid Or VinegarFinally, some cheeses like Ricotta are coagulated using simple lemon juice or vinegar. However, this coagulant is mostly used for a heat-precipitated curd. These coagulants are decidedly vegetarian and have very limited use due to limitations and noticeable taste profile.
Information courtesy of the American Cheese Society