Modern Rennet

MODERN RENNET: Until 1990, cheese rennet was produced the old fashioned way (from abomasums), from various "vegetable" rennets (some of which, called microbial coagulant, are made from the microorganism Mucor miehei.) These days, at a cost one tenth of that before 1990, chymosin is produced by genetically engineered bacteria into which the gene for this enzyme has been inserted. When the bacteria are grown in large vats,they secrete rennin, and itis then purified for cheese making. Cheese Rennet is available commercially in tablet or in liquid form. You will find some cheese makers on the web who prefer liquid rennet and disparage the use of rennet tablets. Perhaps, if you are making hundreds of gallons of milk into cheese, buying bulk liquid would make sense, but for making one to ten gallons of milk into cheese, the tablets make sense.

History of Rennet

HISTORY OF CHEESE RENNET: Presumably, the first cheese was produced by accident when the ancients stored milk in a bag made from the stomach of a young goat, sheep or cow. They found that the day-old milk would curdle in the bag (stomach), yielding solid chunks (curds) and liquid (whey). Once they discovered that the curd-chunks could be separated out and dried, they had discovered a means by which milk, an extremely perishable food, could be preserved for later use. The addition of salt was found to preserve these dried curds for long periods of time.
At some point, someone discovered that the most active portion of the young animal's stomach to cause curdling was the abomasum, the last of the four chambers of the stomach of a ruminant animal. (In sequence, the four chambers are rumen, reticulum, omasum and abomasum.) In particular, the abomasum from a suckling kid or calf was especially active. The abomasum was cut it into strips, salted and dried. A small piece would be added to milk in order to turn it into curds and whey.