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PrintRennet and Coagulating Enzymes
What are coagulating enzymes and how do they create cheese?
In order for milk to coagulate and eventually become cheese, enzymes must be added to breakdown the proteins that keep milk a liquid. Some enzymes do this better than others, but all of these enzymes are in the protein breaking subclass known as proteases. The best proteases or coagulants for making cheese are the type that break a specific protein called kappa casein. When the kappa casein is broken the milk loses its liquid infrastructure and begins to coagulate.
What are Rennet, Rennin, and Chymosin?
Rennet is defined in Webster's Unabridged Dictionary as "the lining membrane of the fourth stomach of the calf (and/or) a preparation or extract of the rennet membrane, used to curdle milk, as in making cheese…." Rennet is also used broadly to describe any enzyme used for the coagulation of milk in the process of making cheese.
Rennin is defined as "a coagulating enzyme occurring in the gastric juice of the calf, forming the active principal of rennet and able to curdle milk." The cheese industry uses a broader definition of the term rennin, referring to it as "any enzyme used for the controlled coagulation of milk."
Chymosin, often used as another word for rennin, is the most common enzyme recovered from rennet.
Types Of Coagulating Enzymes Used To Make Cheese
Animal rennin is the coagulating enzyme (rennin or chymosin) that is harvested from the stomachs of calves.
Vegetable rennet is a misnomer given that the definition of rennet recognizes it strictly as an animal derived substance. Although cheese has been made using enzymes from the Lady Bedstraw, Stinging Nettle, and Thistle flower, the term vegetable rennet is most commonly used when describing enzymes produced using microbes. "Vegetable rennet" is sometimes used more generally to describe any non-animal rennet.
Microbial rennets are enzymes derived from a controlled fermentation of a fungus (e.g., Mucor Pusillus, Mucor Miehi, and Endothia Cryphonectria) or microbial rennets. However, microbial rennets cannot be used to produce cheddar or hard cheeses, limiting their application as an alternative to animal or bioengineered rennets.
Genetically engineered rennets. Shortages and fluctuations in the available supplies of calf rennet prompted the development of genetically engineered rennet. Food scientists can however produce a continuous and pure source of microbial chymosin by incorporating a calf's prochymosin gene into a microorganism. The first microbial chymosin was affirmed GRAS (generally recognized as safe) by the FDA in 1989, with many others following shortly thereafter. Currently, it is estimated that 50% of the chymosin used is produced by transgenic means.
Rennetless. The term "rennetless" is used to mean two things in the cheese world. First, rennetless cheeses are also called "acid precipitated cheeses" and include cottage cheese, ricotta, and some mozzarella. These types of cheese are created using their natural acid levels and do not require the addition of a coagulating enzyme. The second interpretation of "rennetless" cheese is any cheese made without the use of animal derived coagulants.
Why Is Rennet Controversial?
Historically rennet was extracted from calf stomachs by killing the calves, cutting the stomach into strips, scraping the lining to remove surface fat, stretching it onto racks where moisture is removed, grinding it and then finally mixing it with a salt solution until the rennin is extracted. Today the use of animal rennin is controversial to a variety of cheese consumers. The main positions are subdivided below.
Animal rights. Animal rights activists argue that it is inhumane to kill calves for their stomach enzymes, especially when there are several alternative coagulants available to make cheese. These activists would argue that if you eat cheese, then purchase one that is made using cloned or microbial enzymes.
Vegetarianism. Vegetarians can have a confusing time trying to figure out what type of coagulant is acceptable in their cheese. While some vegetarians would strictly adhere to a non-dairy diet, others who eat dairy are content to allow microbial coagulants and some can accept cloned chymosin as a reasonable alternative to using calf rennet. Several vegetarian organizations accept the use of cloned animal enzymes as a reasonable alternative to the animal rennet derived from the killing of calves.
Bioengineering. Genetic engineering has brought new ways to create chymosin for use in cheese making. Originally, a prochymosin gene was injected into a host strain of E Coli K-12, creating a tiny enzyme factory that produced an extremely pure and recoverable chymosin for use in cheese production. Current technology cuts genes from a calf cell and injects it into the genomes of bacteria and yeast. This produces high quality chymosin that is not subject to the volatile market for animal derived rennet. It is estimated that 70% of domestic cheese is produced with bioengineered chymosin. For a consumer who does not want bioengineered foods, animal or microbial rennet should be their choice.
Religion. Some orthodox religions (Jewish and Islam) have specific requirements and prohibitions for the consumption of meat products that can preclude the use of animal rennet. For example, information received from Dr. Chaudry of the Islamic Food and Nutrition Council of America (IFNCA), stated that for a food to be "Halal" (permitted for consumption by Muslims), it must be void of certain animal products and processing procedures. In this case, cheeses that are made from animal rennet are only excluded if the calf is slaughtered improperly or is contaminated with other prohibited ingredients or procedures. The IFNCA recommends the use of microbial or bioengineered chymosin for cheese making.
Current Problems With Cheese Coagulants
There are two major problems that arise for consumers and buyers when trying to distinguish the types of rennet in a particular cheese.
Labeling. There is no requirement for a cheese ingredient label to distinguish between the types of rennet that it may or may not contain. In fact, a cursory review of cheese labels at our 6th and Lamar store in Austin, Texas revealed at least 8 different ways that the coagulating enzymes were identified. They include, enzymes, microbial enzymes, microbial enzymes (non-animal, rennetless), rennetless, rennet, enzymes and rennet, vegetarian rennet, and microbial coagulants. A significant portion of the surveyed cheese labels simply said enzymes, while several labels did not list the type of coagulant used at all.
Obviously this type of labeling hurts cheese buyers as well as consumers. For a store cheese buyer, it is a challenge to track down cheeses that list the type(s) of coagulants used, while for the consumer, buying cheese products with a full understanding of the ingredients is next to impossible. Some companies have taken the time to list whether the cheese they make contains a particular type of enzyme, but these are few and far between.
Enzyme mixing. Compounding the labeling problem is the fact that cheese producers can mix animal, plant, and microbial enzymes under one ingredient listing called "enzymes". The FDA determined that it would be impractical for individual cheese packers to have on hand all the variations of labels needed to properly designate all cheese enzyme mixtures.