下面是我查詢出來的文章，有提到rennet的現代製法。其實從牛的胃裡頭取出來的是傳統製法，應該不符合經濟效益。
新的生產法是透過細菌來生產，至於利用此法來製造是否符合素食的定義，就見仁見智了。
文章的來源出處。(
http://biology.clc.uc.edu/fankhauser/Cheese/Rennet/Rennet.html)
I have received countless questions about rennet (also called rennin or chymosin), and am therefore posting a page on it.
First a little background:
HISTORY OF 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 theabomasum, 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 and dried. A small piecewould be added to milk in order to turn it into curds and whey. At some point, the Germans began calling this material rennen, meaning to run together, or to coagulate. The technical term for rennin is chymosin. Here is a technical description of its action on the various proteins in milk.
MODERN RENNET: Until 1990, 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. 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. I have never had any problems using rennet tablets in making a wide variety of cheeses, and since it is a principle of mine to try to use materials which are readily available locally, I have used tablets for years.
JUNKET RENNET TABLETS: I prefer Junket Rennet tablets because they are readily available and inexpensive. They are easily measured out (1 tablet will coalgulate 5 gallons of inoculated milk) are stable because they are in dry tablets. They can often be found in the pudding section of your supermarket. If they are not there, ask the manager if he or she would please order them. Most managers are willing to do so. (My local Kroger's Store here in Cincinnati has been very cooperative over the years.) If you have no success at your local store, you can order directly from Redco Foods, Inc., P.O. Box 879, Windsor, CT 06095 (formerly the Salada Foods Division). You can order the tablets directly at 1-800-556-6674. I have contacted them by email, and here is their response . "Junket Rennet Tablets" come in a packages of 8 (6.5 g) or 12 tablets. Here is what the back of the package looks like. (Here is a page on Junket Dessert products . The page on cheese is in the works.)
LIQUID RENNET: One teaspoon of liquid rennet is reported to be equivalent to one Junket Rennet tablet. Thus, you would use one teaspoon to coagulate five gallons of inoculated milk, or 4 drops/gallon of inoculated milk. (I have only used tablet rennet, but am assured that liquid rennet works just as well as the tablets.) Liquid rennet can be ordered from various cheese maker's suppliers or which New England Cheese Making Supplies is prominent on the web. I have heard (but have no personal experience) that the liquid rennet looses its potency with age, and one must add more and more to acheive the same degree of coagulating.
MICROBIAL RENNET: A rennet of bacterial origin, called microbial coagulant, is made from Mucor miehei. This tableted rennet should pose no problem for vegetarians. I have never used it but here is some information on it , and also a place to order it.
