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 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. Here is a page about my experiments at making home made rennin. 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 use Junket Rennet tablets because they are readily available, inexpensive and they work. They are easily measured out (1 fresh tablet will coalgulate 5 gallons of inoculated milk) and, because they are dehydrated, they are stable at a cool temperature for several years. They can often be found in the pudding section of your supermarket. The front front and back of the package is shown at the top of the page. If you do not find them on the shelf, 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 the tablets through Redco’s web page, by phone at 1-800-556-6674, or directly by snail mail from Redco Foods, Inc., P.O. Box 879, Windsor, CT 06095 (formerly the Salada Foods Division). Be sure to order the plain rennet, not the pudding mixes. “Junket Rennet Tablets” come in a packages of 8 (6.5 g) or (used to be) 12 tablets. Their page on recipes using Junket rennet includes several cheese recipes which I wrote for them. Here is their page on Junket Rennet Tablets.
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 had a number of cheese makers complain that the liquid rennet looses its potency within a year of 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 from a company called Danlac.
USE OF JUNKET TABLETS: They come packaged sealed in foil. One tablet will clabber 5 gallons of inoculated milk. To use it, you dissolve the tablet in a small amount of water (1 tablet in 1/4 cup fresh clean water). The solution will be slightly cloudy . Look for and crush undissolved chunks at the bottom of the glass. The dissolved rennet is then stirred into the inoculated milk .