Rennet is used in cheese making to coagulate the milk protein and form solids or curds. The curds are separated from the liquid and processed into cheese. Rennet is traditionally obtained from a calf's stomach. Vegetarian versions of rennet are prepared from fungi, bacteria or the genetic modification of microorganisms.
Traditional Sources
Rennet was traditionally isolated from the fourth stomach of young calves. The enzyme chymosin, or rennin, is the active ingredient that aids in milk digestion and absorption. The stomachs of older cows do not contain rennin. The Vegetarian Society of the United Kingdom credits a predicted shortage of calves in the 1960s with the development of alternate sources of rennet.
Fungal and Bacterial Sources
Microorganisms are grown in large vats and secrete rennin. Three main fungi are used to produce a vegetarian form of rennet: Rhizomucor miehei, Endothia parasitica and Rhizomucor pusillus. Rennet produced using the microorganism Mucor miehei is called "microbial coagulant" in the food industry. Tablet and liquid forms of rennet are available commercially.
Genetically Modified Sources
The DNA, or genetic code, for the protein chymosin is isolated from calf cells and inserted into yeast cells. The calf DNA serves as a template for the yeast cells to copy and produce chymosin as they grow. The enzyme produced by the yeast is identical to calf chymosin. Professor David B. Fankhauser of Clermont College estimates that the cost to produce rennet by genetically altered bacteria is about 10 percent of the other methods.
Food Safety
Susan K. Harlander of the National Agricultural Biotechnology Council cites rennet as the first biotechnology derived product approved for use in 1990 for the commercial production of cheese. The enzyme is identical to calf rennet, which is considered GRAS, or "generally recognized as safe," by the Food and Drug Administration. The cheese produced using vegetarian rennet is not labeled as GMO, or "genetically modified organism," since it is the enzyme produced by the microorganism that is used.
Animal or Vegetable
The label on cheese usually does not indicate vegetarian or animal rennet. Strict regulations for cheeses like Parmigiano-Reggiano, Grana Padano and Gorgonzola require the use of traditional animal rennet. Alternatives labeled "Parmesan style" hard cheese are available. Production of the Indian cheese paneer uses heat and lemon juice or other acidic foods, rather than rennet, to coagulate the milk protein. The Wisconsin Center for Dairy Research estimates that less than 5 percent of the cheese made in the U.S. is made with rennet from animals.
Member Comments