Rennet, how does it work?
What is rennet? Rennet a substance that contains an enzyme to coagulate milk, but how does it accomplish this alchemy?
Rennet works by modifying the protein within milk. Milk protein is largely from the casein group of proteins. There are four types of casein found in milk, alpha-s1, alpha s2, beta-casein, and kappa-casein. The alpha proteins will naturally precipitate around calcium and form large solid clumps. But milk has calcium, why isn’t it always curdled? The protein kappa-casein interferes with the precipitation of the other proteins as it interacts with them, this keeps the milk flowing.
What the rennet does is basically chop the kappa protein apart, allowing the other proteins to precipitate out of the milk and form a curd.
There are several varieties of rennet available and this can lead to a touch of confusion. Let’s look at the most common types of rennet and how they vary.
Calf rennet: Calf rennet comes from the stomach lining of a calf. When a calf is born it feeds on its mother’s milk. The first stomach of the calf excretes the enzyme chymosin to curdle the milk in order to keep it from flowing to quickly through the digestion track. Calf rennet works well to make any type of cheese, but there are a few downsides. One problem is that calf rennet is more expensive than other types, and second it makes cheese unsuitable for most vegetarians.
Vegetable rennet: One alternative to calf rennet is vegetable rennet. Various plants, such as nettle or fig, contain enzymes to curdle milk. I have not used actual vegetable rennet, most vegetable rennet that you buy are should more properly be called microbial rennet as they are obtained from various fungi. But when I have more data I will talk more about this type of rennet.
Microbial rennet: This rennet is derived from microorganisms such as Mucor Miehei (a fungus). These organisms produce the enzymes to curdle milk and form the cheese. Microbial rennet is widely available, fairly cheap, and vegetarian friendly. I have heard that this type of rennet can add a bitter taste to cheese, especially if it ages a long time, though I personally have not had this problem before.
Bacterially derived rennet, the last category of rennet: From a technological standpoint this rennet is really cool! This rennet is made by adding the chymosin producing gene to bacteria, when these bacteria reproduce the daughters will exude chymosin! This chymosin is identical to what you would get from a newborn calf but involves to animal death! One downside for some people is that it is a GMO food. Interesting side note, most of the commercially made cheese in America uses this type of rennet.
What rennet is best? That is really a personal choice, I hope that the information here can help you decide what will work for your situation and if you have additional questions please ask!
Have a transcendentally beautiful day!
