The term rennet is often associated with cheesemaking. Probably, use of rennet is also linked to the origin of cheesemaking only. Even though there is no conclusive evidence with regard to the origin of cheesemaking, it can be traced back to 8000 BC, when humans started domesticating sheep, goats, and cows. It is believed that it was an accidental discovery, as people used to store milk in bags made from the stomachs of animals, like cows, sheep, and goats. The stored milk turned into curds and whey, due to the action of rennin, an enzyme in the stomach lining. They realized that milk can be preserved through curdling and drying of the curds. The origin of cheesemaking is also linked to the practice of salting curds for preservation. This product was later termed cheese. However, the factor that aids in curdling remained unidentified.
Origin of Rennet
Cheesemaking continued for decades, and at some point, somebody identified that among the four chambers in the cow's stomach, the fourth one called abomasum has a prominent role in curdling milk, as compared to the other chambers. It was also noticed that the abomasum of an unweaned (suckling) calf was more active in this process. So, people started preserving the abomasum of unweaned calves, by cutting them into small pieces, which were salted and dried. Such small strips of dried abomasum were added to the milk as one of the primary steps of cheesemaking process. These strips were called rennet. The term rennet is derived from the German word, rennen, which means, 'to coagulate'. Even today, some of the traditional cheesemakers follow this method for coagulating milk. However, they prepare a filtered solution from the cow's stomach immersed in saltwater or whey, for a stipulated period. Around one gram of this solution is sufficient for coagulating two to four liters of milk.
What is Rennet
Rennet is an enzyme complex, which is produced in the stomach of young mammals. This enzyme complex helps them in digesting mother's milk. This complex consists of many enzymes, like protease, pepsin, and lipase. However, the most prominent among these enzymes is chymosin or rennin.
The traditional methods of rennet production gave way to the modern ways. Now, cows' stomachs are frozen and milled, before treating with an enzyme extracting solution. Then crude rennet is extracted, and is treated with acid. The rennet extract is filtered numerous times after neutralization of the acid. Then it is concentrated to a potency of 1:15000, which means that one gram of this rennet extract can coagulate 15,000 liters of milk.
Nowadays, rennet extract is available as tablets and in liquid form. Rennet tablets are medium-sized, and are whitish in color. Usually, these tablets come in strips, and each tablet is scored into four divisions. As per requirement, rennet tablets can be added to milk, partly or wholly. It is dissolved in cold water, and is then added to the milk. Only cold water is used for dissolving these tablets, as any type of heat can deactivate the enzymes in the tablet. Once the tablets are dissolved, the water is added to the milk, which is left undisturbed for at least 24 hours. Any type of disruption may affect the process of coagulation.
Types of Rennet Tablets
Till the last decade of the twentieth century, rennet was produced through traditional methods. Later, modern technology was incorporated in this area too. Inadequate supply of cows' stomachs led to the research for alternative methods. Vegetable rennet was made from the enzymes in certain plants, but the most widely used vegetable rennet is made from a particular type of mold, called Mucor miehei. Though classified as a vegetable rennet, it is actually a microbial rennet. Another type is the genetically engineered rennet, which is made from genetically modified microorganisms, that are induced to produce chymosin in large amounts.
There are various brands of rennet tablets available in the market. Try to buy good quality tablets from reputed cheesemaking supply companies. Rennet can also be purchased online.