Types of rennet and their effects on cheese production

¶ … Rennet on Cheese Production and Ripening

Rennet was supposedly accidentally discovered centuries ago. Since that time, humans have used rennet to create a "version" of milk that is more easily preserved in many varieties, flavors and textures. Though natural rennet was chiefly used throughout History, vegetable rennet was also prepared and used for centuries. More recently, due to the steadily increasing popularity of cheese and the inability of natural rennet production to meet that popularity, science has also created microbial rennet and genetically engineered rennet. Through refinement of genetically engineered rennet, in particular, the modern cheese industry is able to produce cheese that works like natural rennet and produces a natural flavor and texture.

Types of Commonly Used Rennet Preparations

The type of rennet concentration, along with pH, temperature, cutting time and curd washing, are all factors affecting curd formation (Janhoj & Qvist, n.d., pp. 20-22). The effects of different types of rennet are examined through the microscopic examination of sample slides, observations during each process of cheese production and review of published scientific studies.

a. Natural Calf, Lamb and Kid Rennet

Calf, lamb and kid rennet are enzymatic coagulants taken from the stomachs of young cows, sheep and goats (Ardo & Waagner, 2011, pp. 41-42). Traditionally used in the manufacture of cheese, this type of rennet contains two proteolytic enzymes: chymosin and pepsin. Chymosin coagulates milk by hydrolyzing K-casein at its Phe105-Met106 bond. K-casein or "Kappa casein" is a hydrophobic protein that tends to keep milk soluble and uncoagulated. The introduction of Chymosin renders k-casein inactive, converts it to para-kappa-casein and a macropeptide. Since Para-kappa-casein cannot stabilize the micellar structure of milk, the milk-insoluble caseins precipitate, creating curds (Bowen, 1996).

A chart showing the process of cheese production using calf rennet follows:

(New Zealand Institute of Chemistry, 2008, p. 3)

b. Vegetable Rennet

As cheese use increased and production of traditional rennet failed to meet that increasing need; therefore, other types of rennet were used (Ardo & Waagner, 2011, p. 43). The resulting caseins from these types of enzyme preparations are all called rennet casein, "and all have similar properties" (New Zealand Institute of Chemistry, 2008, p. 5). Vegetable rennet is not really "new," as it has been used for centuries in other countries, and it is acceptable for the production of vegetarian cheese. The type of vegetable rennet made today is normally a "Microbial Rennet" (Fankhauser, 2002).

c. Microbial Rennet

Another type of rennet used in the production of cheese is Microbial Rennet (Ardo & Waagner, 2011, p. 43), which is normally created using a mold such as Rhizomucor miehei. This mold is created within a fermenter and is then concentrated and purified to create proteolytic enzymes for cheese production. In this instance, the microbial rennet helps create curds by preventing k-casein's ability to keep milk soluble and forcing the milk's coagulation. Microbial rennet tends to create a more bitter cheese (Agboola, Chen, & Zhao, 2004, p. 567).

3. Conclusion

A centuries-old discovery, rennet has remained a staple for the world's production of cheese. In addition, adapting to increasing demand, cheese producers and scientists have experimented with rennet sources other than natural calf, lamb and/or kid rennet. Experimenting and refining cheese processing, cheese makers and scientists have used vegetable rennet, microbial rennet and genetically engineered rennet, particularly refining genetically engineered rennet. The result is a cheese making process with genetic engineering that acts like the age-old process using natural rennet; furthermore, when combined with natural pepsin, this newer process can create a natural texture and taste in cheese.