Vegetarian cheeses are manufactured using rennet from either fungal or bacterial sources. Advances in genetic engineering processes means they may now also be made using chymosin produced by genetically altered micro-organisms.Vegetarian cheeses are made with rennets of non-animal origin. In the past, fig leaves, melon, wild thistle and safflower have all supplied plant rennets for cheese making. However, most widely available vegetarian cheeses are made using rennet produced by fermentation of the fungus Mucor miehei. Vegetarian cheese may also be made using a rennet from the bacteria Bacillus subtilis or Bacillus prodigiosum.Advances in genetic engineering techniques mean that some vegetarian cheeses may now be made using chymosin produced by genetically engineered micro-organisms. The genetic material (DNA) which encodes for chymosin is introduced into a micro-organism which can then be cultured to produce commercial quantities of chymosin. This is done by extracting genetic material from calf stomach cells which acts as a template for producing the chymosin encoding DNA. This can then be introduced into the micro-organism. Once the genetic material is introduced there is no further need for calf cells. Alternatively, the chymosin encoding DNA can be bio-synthesised in the laboratory without the use of calf cells.The chymosin produced is identical to that produced by calf stomach cells. The development of genetically engineered chymosin has been encouraged by shortages and fluctuations in cost of rennet from calves. It's manufacturers claim that genetically engineered chymosin will end the cheese making industry's reliance on the slaughter of calves.Chymosin encoding DNA has been introduced into three different micro-organisms. These are the yeast Kluyveromyces lactis, the fungus Aspergillus niger var awamori, and a strain of the bacteria Escherichia coli. All of these have now been approved and cleared for use by the Ministry of Agriculture, Fisheries & Food. There is no legal requirement for manufacturers to state whether a genetically engineered rennet has been used in the cheese making process.
If you are vegetarian, look for cheese made with microbial rennet or made with rennet derived from plants. Typically, plant-based rennet for cheese comes from thistle. Microbial rennet is usually fermented from bacteria but can also be genetically modified. For guidance, consult this list of artisanal cheeses made with vegetarian rennet.
Rennet is an enzyme used to coagulate (thicken) milk during the cheesemaking process so that curds form. Rennet is derived from one of four sources: 1. The stomach lining of a young animal (a calf, ewe or kid.) The enzyme rennin is found in the stomach lining of animals because it aids in the digestion of their mother's milk. This type of rennet is usually called “traditional” on cheese labels. 2. Plants (typically thistle) 3. Microbes in fungus and yeast (called microbial on cheese labels) 4. Genetically engineered rennet that imitates animal rennet but is not derived from animalsIf you're a strict vegetarian, you will want to avoid artisanal cheese made with “traditional” (animal) rennet. Look for cheese with rennet that is made from plants or microbes. Unfortunately, this information is not always on the labels of cheese that has been pre-cut and wrapped by a store. Often, however, the information is printed on the large label on a whole wheel of cheese. A good cheese store will be able to provide information about which cheeses are vegetarian.
