What is Rennet?
Rennet is a complex of natural enzymes which is used in the manufacturing of cheeses. It's produced in the stomachs of mammals and its primary function is the digestion of mother's milk. Rennet contains several enzymes, one of which is protease which coagulates the milk and then separates into curds and whey (solids and liquids respectively). Chymosin or Rennin is the active enzyme, but lipase and pepsin are other important enzymes also found in rennet. Additionally, where the vegetarian ethic is concerned, there are alternative sources of rennet that are non-animal in nature and is fit for their consumption.
Alternative Rennet sources
Dating back to ancient Roman times, cheese makers have always looked for alternative sources of rennet based on the increasingly limited availability of calf stomachs used in the production of rennet. Other sources of these enzymes include fungi, microbial sources, and plants all of which can be substituted for animal rennet. Lacto-Vegetarians find cheeses that are produced from these sources suitable for consumption.
In North America today, industrial cheese makers use a microbial type of rennet known as GMO in the production of most cheeses because it is more cost-effective than rennet from an animal source. Conversely, and due to tradition, cheese making in Europe today still uses animal rennet most of the time. The following is a list of 3 of the more common alternative sources of rennet.
Vegetable rennet - from a historical standpoint, the Greek poet Homer made mention of using the juice of figs for the coagulating of milk in his epic "The Iliad", and even today, it is common knowledge that coagulating properties can be found in numerous plants. Some of these plants which have the ability to coagulate include Ground Ivy (or Creeping Charlie), certain nettles, and thistles, the enzymes from which are used in the production of cheeses from the Mediterranean region.
On a cautionary note, unfermented soybeans which produce Phytic acid found in GM soy rennet should be avoided by those who have soy-based allergies. Additionally, vegetarians find vegetable rennet as a suitable component and even Kosher cheeses can be made using this type of rennet. However, genetically modified or microbial rennet is typically used in the making of Kosher cheeses.
Microbial rennet - certain molds are capable of producing proteolytic enzymes which assist in the break down of proteins into much simpler compounds such as during the digestive process. In order to avoid contamination with some of the unpleasant byproducts resulting from the growth of molds, the molds get produced in a fermenter and then are specially purified and concentrated. Characteristically, cheeses manufactured with the use of microbial rennet tend to taste somewhat bitter.
Genetically-engineered rennet - basically, some producers sought out other replacement sources of rennet due to the numerous imperfections found in microbial and vegetable rennet. By employing genetic engineering, it was possible to modify certain bacteria, fungi, or yeasts by using the genes of calves so they would produce chymosin or rennin. Roughly 80% to 90% of all the commercially made cheese in the US in 2008 used a genetically-engineered product called GMO-based rennet.
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