In Quicke’s vat, this arrangement has broken down and become curds and whey, on its way to cheddar. If milk is left alone, bacteria quickly start converting its lactose sugar into lactic acid that can eventually start this curdling. This is probably how cheese was first made, but modern needs for safe storage and maturing demand a different approach. Quicke’s minimally pasteurises its milk, and like most modern cheesemakers adds a starter culture including lactic acid bacteria such as Streptococcus, Lactococcus and Lactobacillus. They work hand-in-hand to control which bacteria reach the final cheese, by outcompeting less welcome species and making the environment too acidic for them. And rather than these bacteria doing the curdling, acid conditions help an enzyme preparation known as rennet to do it. Their ongoing acidity development also controls the resulting solid curd’s texture.Had some nice goats cheese at dinner tonight, as it happens.
Traditional rennet, which Quicke’s uses, comes from soaking a milk-fed calf’s stomach in brine.
UPDATE: I was wondering last night how someone first worked out that calf's stomach contained something that was useful in making cheese. Another site provides the likely answer:
There is a great deal of mythology surrounding the history of cheesemaking, because humans have been making it for a very long time, and the steps involved are actually fairly complicated. The stomachs of ruminants have historically been used to make bags and sacks, and food historians theorize that someone must have stored milk in one a bit too long, allowing it to curdle, and the curdled milk was then turned into a food product. Modern rennet is created through an extraction process that yields neat, dry tablets or a liquid that is very easy to work with.
Traditional rennet was made by washing the stomach of a young ruminant after it has been slaughtered, and then salting it. The salted stomach is kept in dried form, with cooks snipping off small pieces and soaking them in water when they have a need for the extract. Some cheesemakers continue to make and use it in this way, but the vast majority use commercially processed rennet, which is made by creating a slurry and then subjecting it to a compound that will cause the enzymes to precipitate out.