Rennet! What a wonderful thing!
What’s rennet, you ask? Well! I’m glad you did.
Rennet is a combination of enzymes, usually extracted from the stomachs of mammals (read: fleishig or meat), which breaks down proteins in milk to separate them into milk solids and liquid (also known as Curds and Whey – made famous by Little Miss Muffet). The principal enzyme in this process is called chymosin and it is responsible for breaking down the protein casein. Without getting into the whole process, the addition of rennet into milk causes the formation of curds which eventually get separated from the whey and processed into a whole variety of various cheeses.
In order to really appreciate cheese, one must delve into the history of food for just a moment. It appears that cheese was actually discovered by mistake (much like the ancient Egyptians accidentally discovered beer). Before the advent of clay or modern storage containers, ancient civilizations would often use the skins or stomachs of animals as bags. What they discovered was that day-old milk, left in the stomach-bags, had the interesting effect of curdling and forming the curds and whey. When they figured out how to separate and dry the curds, they found an effective (and I daresay, delicious,) means of preserving milk. Fast-forward a few centuries, and this process has undergone an amazing evolution to provide us with the multitudes of cheeses from all over the world (except maybe Japan and the Philippines).
It appears that there are 3 forms of rennet: vegetable/fungal, microbial, and animal-derived. The first, vegetable or fungal rennet is an enzyme that is extracted from various plants or fungii (mushrooms) and have the similar properties of animal-derived rennet. This is suitable for vegetarians, and under the right circumstances, considered Kosher. Microbial rennet is when a bacteria is added to milk to achieve the same separation, but it has the unwanted side-effect of creating bitter-tasting cheese after prolonged periods. However, GM rennet, also known as a Genetically Modified microbial rennet, is when they genetically modify a bacterial source to produce the genetically similar enzyme that is found in animal-derived rennet. This eliminates the problem of bitter cheese, with the added benefit that is is vegetarian- and kosher-suitable. The last, of course, is the traditional means of making cheese, by extracting the rennet from mammal stomachs – a process that varies from one company to the next – and is usually found in tablet or liquid form.
Now, it seems that there is a liquid GMO Chymosin (microbial rennet) that is OU certified (produced by Chr. Hansen) and is completely pareve. This liquid rennet is actually available for purchase by a company called Kelley Supply. So, those of you with a hankering for making some homemade cheeses – now’s your chance to make some!
There is one other method of making cheese and that’s with an acid coagulation. When the pH balance of milk shifts drastically into the acidic pH range (0 – 7 pH), it causes a similar effect as adding rennet to the milk. The proteins change, and separate into milk solids and liquid. In fact, if you’ve ever left milk in your refrigerator past its due date, you’ve probably experienced a rancid smell and chunkiness – that’s separated curds and whey – although given the circumstances in which it was formed, I’d highly recommend against ingestion as I’m sure it’s not very palatable.