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An update on Rennet.

RENNET IS DEFINED AS THE INNER LINING OF THE fourth stomach of calves and other young ruminants or as an extract made from the stomach lining of a ruminant, used in cheesemaking to curdle milk. Rennet also broadly refers to any enzyme used for the coagulation of milk in the cheesemaking process. The active component in rennet is known as rennin, the actual enzyme that causes milk to coagulate. This enzyme must be added to break down the proteins that keep milk in its liquid form. Dean Sommer, a Cheese and Food Technologist at the Wisconsin Center for Dairy Research (WCDR), estimates that 5-10 percent of the rennet is retained in the cheese curds, while the rest stays in the liquid whey.

Organic Valley, a major producer of organic cheeses in the United States, told us, "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." The rennin (also known as chymosin) was needed to coagulate milk during the cheesemaking process, allowing the liquid whey to be removed from the curds that are later pressed into cheese. Some small cheese operations wishing to maintain tradition, especially those in Europe but even in the United States, still produce cheese in this manner.

According to the WCDR, some people, namely traditional cheesemakers and some artisan and specialty cheesemakers, continue to believe that calf rennet produces the best-flavored aged cheeses, especially aged cheddar, Parmesan, and others. In fact, veal calf rennet was once considered the "Cadillac of rennets" and secured the highest price among all milk coagulants.

Rennet is used only for making certain types of cheese. Other dairy products, such as ice cream, sour cream, and yogurt, are not made with rennet.


Steve Lutzke of Chr. Hansen, a leading enzyme company, said the supply of animal rennet was consistently high through the 1970s. Since its price was reasonable, cheesemakers had no reason to look for alternatives. Consequently, the majority of cheese produced in the United States at that time was made with animal rennet.

According to Lutzke, the 1980s saw animal rennet supplies become more inconsistent, resulting in price fluctuations and even product shortages. Dave Potter of Dairy Connection, Inc., of Wisconsin, a supplier of enzymes to many cheesemakers, attributed the decline of calf rennet use in cheesemaking and the inconsistent supplies of the animal enzyme to the faltering veal industry, which became more unstable in the '70s due to the animal protection movement. Rennet produced by microbial (specifically fungal) fermentation became more available. Approximately half of all rennet used in the '80s was microbial.

By the 1990s, the animal rennet supply became even more inconsistent, making the price of animal rennet very high. The cheese industry had the economic incentive to transition away from animal rennet usage and so the turn toward microbially-derived rennet continued rapidly until, by the end of the decade, almost all cheese in the U.S. was made using microbial rennet. Microbially-derived rennet was also found to be purer than animal-derived rennet, resulting in more consistent cheese production.


According to the WCDR, there are four types of rennet: calf rennet, microbial rennet, fermentation-produced chymosin, and vegetable coagulants.

Calf Rennet

Calf rennet has traditionally been the enzyme of choice in cheesemaking. However, between supply problems and animal rights, religious, and food safety issues, calf rennet is now used to make less than 5 percent of all cheese produced in the United States today, according to the WCDR. In other words, approximately 95 percent of all cheese in the United States is made with non-animal-derived rennet.

Microbial Rennet

Microbial rennets are those produced by fungi, such as Rhizomucor miehei. Typically, these rennets are less expensive than calf rennet, but they lack the same protein breakdown specificity that calf rennet has. This results in smaller cheese yields and, as a side effect, a somewhat bitter taste to the final cheese product. Microbial rennets also have other chemical and physical properties, such as increased heat resistance and residual amylase (an enzyme responsible for starch breakdown) activity, that can lead to functional problems in some foods to which whey had been added. However, microbial rennet manufacturers report that most of these issues have been resolved.

Fermentation-Produced Chymosin

Fermentation-produced chymosin (FPC) is by far the most common form of a milk-coagulating enzyme used today, according to the WCDR. Potter said that approximately 70 percent of all cheese is produced with FPC, while approximately 25 percent is made with microbial coagulants and the remaining 5 percent is made from calf rennet.

Of all the types of rennet, FPC most closely performs like calf rennet in cheesemaking because of similarities in chemical action and structure. It is not, strictly speaking, like the microbial rennets described above, although it also is produced by a fermentation process. Unlike microbial rennet, FPC is produced by genetically-modified microorganisms. The microbes are removed from the final product after extraction, purification, and standardization of the chymosin; therefore, the chymosin is not generally considered a GMO product.

FPC costs more than microbial rennet but less than calf rennet. Many in the cheese industry feel it produces a cheese of equal quality to that produced by calf rennet. Because it is a fermentation product, the raw materials for its production are readily available, resulting in a stable supply at a consistent price for the cheese industry.

Vegetable Coagulants

In parts of Europe, vegetable coagulants are used to make cheese. These are produced by plants such as cynara, a type of thistle.


Recently, The VRG did an update (VJ, Issue 4, 2007) on bone char in the sugar industry. We discovered that USDA certified organic sugar has never passed through a bone char filter and, therefore, is always vegan. We wondered if we could make an analogous claim about USDA certified organic cheeses with respect to animal rennet, i.e., that animal rennet is never used in organic cheeses. The short answer is 'no.'

Most organic cheesemakers with whom we spoke market their cheeses simply as "USDA Certified Organic" without specifying whether that cheese is, according to the USDA's classification scheme, 100 percent, 95 percent, or at least 70 percent organic or if it's "Made with Organic Ingredients." In practically every case, it appears from our survey of many organic cheese companies that today's "USDA Certified Organic" cheese is almost never 100 percent organic. Readers may note that, to use the phrase "USDA Certified Organic," at least 95 percent of a product's ingredients must be organic.

It is the presence of a very small quantity of non-organic rennet (and, in some cases, non-organic processing aids and/or preservatives) that leave the cheesemakers unable to claim that their cheeses are 100 percent "USDA Certified Organic." This is true whether the rennet is animal or microbially derived. In most cases, organic cheesemakers today use microbially derived rennet produced through a fermentation process (i.e., the 'microbial rennet' described above). According to the National Organic Program (NOP), this fungal-derived rennet is not a genetically-engineered organism (GMO). The complete prohibition of GMOs in any product labeled "USDA Certified Organic" is a basic tenet of the NOP.

Many cheesemakers label this enzyme as 'vegetable rennet.' According to the WCDR, calling fungal-derived rennet 'vegetable rennet' is a misnomer, but it is still very commonly labeled this way. According to Joan Shaffer of the NOP's media office, the microbially-derived rennet is not something that can be 'organic' since it is not "an agricultural product;" therefore, no cheese made with microbially-derived rennet can ever be 100 percent organic. However, the microbially derived rennet can be in an organic product that is 95 percent or 70 percent organic because it is on the National List of Allowed and Prohibited Substances as an allowed substance that can be used to make or can serve as ingredients in USDA Certified Organic products. (Analogous, USDA Certified Organic sugar on the market today is also "95% Organic" and not "100% Organic" because of the use of a non-organic processing aid that is allowable under NOP rules.)


Concerned readers should also be aware that some organic cheeses, like some non-organic cheeses, may contain other animal-derived enzymes. The most common one is lipase, responsible for breaking up fat molecules. Potter said that lipases are structurally very complex compared to rennets. "Fermentation-derived lipases on the market (today) do not function as well as animal lipases," he commented. "This is because animal lipases are a complex blend of lipases. The arrangement and ratios needed for optimum functionality has not been replicated. The result in cheese is too much of one flavor compound developed and an imbalance of flavor during the cheese ripening process." Thus, most lipases used in cheese today are derived from animals.

Organic Valley, for example, uses microbial rennet and animal-derived lipase in its Romano cheese and Blue Cheese Crumbles. The animal source is not listed on the label. Horizon, a major producer of organic cheese, told us by telephone that they use 'microbial' rennet in all of their cheeses. They did not make any further comment, saying that it was "proprietary information." Kraft Foods, the major non-organic cheese manufacturer in North America, told us that their Parmesan and Romano Cheese Blend is made with 'microbial rennet,' but animal-derived lipase is also used to impart the distinctive flavor to Romano cheese. Again, the animal source is not listed on the label.


According to the enzyme companies, it appears that very little calf rennet (less than 5 percent) is used anymore in the United States. On the other hand, some major cheesemakers have said that calf rennet is still used in several of their cheese varieties. Kraft, by far the largest cheese company in America, said that, when the word 'enzymes' by itself appears on a label, consumers should understand that both animal-derived and microbial-derived enzymes may have been used. They emphasized that the "box in the store" is the best place to find out ingredient information for a specific Kraft product; however, the box often just says 'enzymes,' leaving the consumers in doubt. Kraft told us that when microbial rennet is used, it will be labeled as 'microbial rennet.'

However, on the Kraft website, there is a FAQ sheet that explicitly states that Kraft Macaroni & Cheese does contain enzymes derived from animals (calves and sheep), found in the animals' stomach and intestines. The writer was informed by telephone that this applies to all varieties of Kraft Macaroni & Cheese. A Kraft representative also said that Kraft Natural Swiss and Kraft Grated Parmesan utilize microbial rennet that is NOT made with enzymes extracted from animal tissue. (This is interesting because many other people in the cheese industry told us that Parmesan cheese is one variety that is often made with calf rennet.) As mentioned previously, the Kraft Grated Parmesan Cheese may contain lipase (from an animal source).

In addition, The VRG asked Sargento, another major cheese manufacturer, about the enzymes used in their cheeses. They estimated that 11 percent of their cheese brands "possibly contain" animal rennet. (They did not specify how this percentage was related to their total sales volume.)

For updates on ingredients, subscribe to VRG's e-mail newsletter at <>. Please note that we depend on company statements for product and ingredient information. It is impossible to be completely sure about a statement, information can change, people have different views, and mistakes can be made. Please use your own best judgment about whether a product is suitable for you. To be sure, do further research or confirmation on your own.

By Jeanne Yacoubou, MS, VRG Research Director

Jeanne Yacoubou is The VRG's Research Director. She holds master's degrees in philosophy, chemistry, and education and wrote "Veggie Options at Quick-Service Restaurant Chains" for Issue 2, 2008, of Vegetarian Journal.
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Author:Yacoubou, Jeanne
Publication:Vegetarian Journal
Geographic Code:1USA
Date:Jul 1, 2008
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