As discussed elsewhere, scientists engaged in an active search for rennet substitutes during the latter decades of the twentieth century. One of the outcomes of this search was fermentation-produced calf chymosin.
Fermentation-produced chymosin (FPC) is nature-identical calf chymosin produced by fermentation by a host microorganism in which the gene for the enzyme is expressed.
Originally, three calf FPCs were developed but only two are now on the market. Maxiren is produced by DSM Food Specialties (Delft, Netherlands) while Chy-Max is produced by Chr Hansen (Hoersholm, Denmark). (Some years ago, a third enzyme, produced by Pfizer was sold to Chr Hansen who used Pfizer's name for their own enzyme; originally, the Hansen product was known as "Chymogen".) The gene for calf chymosin is expressed in Aspergillus niger var. awamori for the production of Chy-Max while DSM expresses the gene in Kluyveromyces lactis for the production of Maxiren. More recently, Chr Hansen have introduced a new FPC, Chy-Max M, which is fermentation-produced camel chymosin. This novel coagulant has some very interesting properties. Interestingly, camel chymosin has a higher milk coagulation to general proteolysis ratio on bovine milk than does bovine chymosin! Chy-Max M is perhaps the most interesting and novel coagulant to come on the market for a number of years.
Although FPCs are from the biotechnology industry and are expressed in genetically modified microorganisms (GMOs), it is important to remember that they are products of GMOs and do not contain any living genetically engineered organisms. FPCs are thus in exactly the same category as human insulin, most of which is now produced by a similar approach to FPCs and which diabetics inject directly into their bloodstream.
FPCs are excellent coagulants. The absence of bovine pepsin (always present at variable levels in traditional calf rennets) helps to improve cheese yield. FPCs have Halal, Kosher and vegetarian status, are highly standardised and numerous studies have shown that they are suitable for the manufacture of many varieties. Most Irish Cheddar cheese is now made using FPCs.