Response from Ilovecheese.com
Rennet is used only in cheesemaking, thus both cheese and whey products would contain rennet, while ice cream, sour cream, yogurt or other Grade A products would not contain rennet. There are 4 basic types of rennet: Calf rennet, microbial rennet, fermentation produced chymosin, and vegetable coagulants. Calf rennet was traditionally what most cheesemakers used for coagulant. As the name implies it is extracted from the stomach of veal calves. Some people continue to believe that calf rennet produces the best flavored aged cheeses, such as aged cheddar, parmesan and others. While as recently as 20 years ago calf rennet dominated the market, currently calf rennet accounts for less than 5% of the rennet sold for cheesemaking. It is used primarily by traditional cheesemakers making very high quality aged cheeses as well as by some artisan and specialty cheese operations. Historically veal calf rennet was considered the Cadillac of rennets, and commanded the highest price of all milk coagulants. World supply of and demand for calf stomachs played a large role in significant price fluctuations and even product shortages of calf rennet. This product was not considered acceptable to most Kosher or Halaal organizations. Microbial rennets have also been around for a long time and are produced by some strains of molds such as Mucor miehei. Historically microbial rennets have enjoyed some cost advantages over traditional calf rennet. On the other hand, microbial rennets lack the specificity of proteolytic activity that calf rennet has, which can result in less cheese yield during manufacturing, a significant economic issue for the cheesemaker. This lack of specificity has also resulted in some bitterness defects in cheese made with microbial rennets, particularly aged cheeses. Historically, microbial rennets had more heat tolerance than did calf rennets, which had led to cases where heat treatment of whey post cheesemaking didn't destroy the proteolytic activity of the rennet which led to problems in some applications of use of whey in other food systems. Microbial rennets also at times had some heat resistant residual amylase activity which caused defects when the whey was used in food systems containing starch. However, manufacturers report that most of the heat resistance and amylase problems with this product have been corrected. Microbial rennets are normally accepted by Kosher, Halaal, and Vegetarian organizations. Fermentation produced chymosin (FPC) currently dominates the market (about 90+%). This product most closely resembles veal calf rennet in its chemical action, structure, as well as its performance during cheesemaking. While many people casually refer to this product as a microbial rennet, it is fundamentally different from the true microbial rennet coagulant described above and is not generally called microbial rennet by the manufacturers and distributors of this product. FPC is produced in a fermentation process by genetically modified micro-organisms. These microbes produce chymosin during the fermentation process after which the chymosin is extracted, purified and standardized in strength. This process produces an extremely pure chymosin with no traces of the modified micro-organisms, and thus is normally not considered a GMO product. Typically this product is priced higher than microbial rennet but less that the traditional price of calf rennet, and produces a quality of cheese, at least in most cases, considered to be equal to calf rennet. Normally this product is considered acceptable by Kosher and Halaal organizations. Because it is produced in a fermentation process the raw materials for the process are not limiting as they are in the case of calf rennet, so production of FPC has resulted in a stable supply of rennet for a growing cheese industry, and also reasonable stability of prices. Vegetable Coagulants are produced by plants such as the Cynara, a type of thistle. This type of coagulant is rarely used in the United States, although it is used in some parts of Europe. This type of rennet is very proteolytic and is prone to bitterness.