Enzymes in cheese production

Say cheese!!

Cottage cheese, blue cheese, mozzarella, cheddar, camembert…the list is endless! The steps of producing cheese have many varieties, according to the flavor and age of the cheese. However, all of the possible processes have one common factor: the usage of enzymes to separate creamy lumps, the curd, from the liquid, the whey from milk.


How are enzymes involved?

The enzyme used in cheese production is rennet. Rennet, also referred to as rennin or chymosin, is a complex of several different enzymes that are found in the stomach of mammals. These enzymes, including pepsin and lipase, help young mammals to digest the milk consumed from the mother. Pepsin is a digestive protease, also a type of enzyme, that is given off by cells in order to digest food proteins. Lipase is an enzyme that acts on lipid substrates; in human bodies, it breaks down the fats in the digestive system. The two enzymes use their characteristics to help separate the milk into curd and whey.

rennin.jpg renin, chymosin

Before rennet is added, the milk is pasteurized at 72℃ for approximately 15 seconds to kill off all harmful bacteria. Then it is cooled down to 30℃ to add lactic acid bacteria which will help the milk coagulate, becoming thicker and solidified. The lactic acid bacteria is also said to improve the taste consistency of the produced cheese.Rennet, most common in the form of powder or tablets, is added to the milk. Once the rennet is stirred in, the milk soon turns into curds and an unclear liquid, as shown in the picture. What occurs inside the milk is that the rennet enzyme acts on its substrate, casein. Rennet is the catalyst for the conversion of casein into para-casein; it removes glycopeptide, a polypeptide involving carbohydrates, from the casein. The para-casein then uses the calcium of the milk to spread out, and incorporates more milk fat and some water to form the white, solid curds. The rate in which this process will occur depends on the strength of the rennet; the usual strength is from 1:10,000 to 1: 15,000 (one part of rennin will coagulate 10~15,000 parts of milk).

curds forming in milk

drained curds

The curds are then collected, mixed together then put into individual clumps to age and become the many different types of cheese we are able to eat deliciously.
Other than production of cheese, rennet is also used to make Junkets; Junkets are desserts made from sweetened and flavored curds.

For a more detailed description of the production process, go here

How is rennet produced?

The traditional way of obtaining rennet was to dry and clean the fourth stomach of newly-born calves, slice it into smaller pieces, then put it into salt water mixed with vinegar or wine. After several days, the solution was filtered to make crude rennet; the crude rennet is capable of coagulating 2000 to 400 grams of milk. 1 kilogram of extracted rennet contains in it about 0.7 grams of enzymes that are active, and has no other organic material in it. It may also contain some Sodium Benzoate for preservation purposes. 1 kilogram of cheese has in it approximately 0.0003 grams of rennet enzymes.


rennet tablets

However, since much of real stomachs are limited alternatives such as vegetable rennet, microbial rennet, genetically engineered rennet, or acid is used more commonly nowadays.
  • Vegetable rennet is extracted from plants that contain a mold called Mucor miehei such as thistles, mallow, and fig tree bark. The rennet taken from plants are useful in that vegetarians are able to consume cheese that is made from the vegetable rennet since it does not involve rennet from animal’s stomach. (further focused information here)
* Microbial rennet is made from Mucor miehei created by a fermenter. This type of rennet produces cheese that has a more bitter taste and is matured for a longer period of time.
  • Genetically engineered rennet is the most innovated. Engineers use genes of calves and apply them to bacteria so that Chymosin is produced. In order for the cheese to taste more natural, the genetically engineered Chymosin is used with naturally produced pepsin.
  • Acid coagulation does not involve rennet, and only lactic acid. Since using acid takes less time and is more affordable, production of cheap mozzarella without maturation usually involves this. Although cheese can still be produced this way, rennet is usually added in order to speed up the process.
> More information on various types of rennet can be found here.