Rennet has different types such as animal, plant-based, microbial, etc.
Animal Rennet
The type of rennet sourced from animals, mostly comprises a coagulating enzyme called chymosin. Naturally present in the fourth stomach of a calf or lamb. Regardless of the animal source, a little chymosin goes a long way: 1 part enzyme to 15,000 parts milk does the job of coagulation.
The production of animal rennet in the traditional way is that the dried and cleaned stomach of young calves is cut into small pieces and placed in salted water or whey with some vinegar to lower the pH. After overnight or several days, the solution is filtered, and the raw rent, which is the result of filtration, is used to coagulate the milk. About one gram of the solution can coagulate 2 to 4 liters of milk. This method of rent production is still used by several cheese makers in Austria, France, Greece, Romania, Switzerland, and the United Kingdom.
A modern method: the frozen stomach of a young calf is ground and placed in an enzyme extraction solution. The extracted solution is activated by adding acid. (The enzyme produced in the stomach is secreted and then activated by stomach acid). then the acidic solution is neutralized, and the extract is filtered and concentrated in several steps until its strength reaches 1: 15000, which means one gram of extract can coagulate 15 kg of milk.
Animal enzymes that coagulate milk include renin, chymosin, pepsin, trypsin, and chymotrypsin.
Plant-based rennet
True plant-based rennet comes from plants such as cardoon thistle, butterwort, artichoke, nettles, safflower, melon, yellow bedstraw, and fig leaves. The challenge of using this coagulant is that its strength varies considerably. It requires a great deal of skill to produce a consistent cheese using plant-based rennet. Also, in terms of flavor, these cheeses frequently develop a slightly bitter taste as they age. These risk factors ensure that plant-based rennet is rarely used for commercial production.
Plant enzymes that coagulate milk include papain, ficin, and bromelain.
Microbial Rennet
The term “rennet” is of animal origin, but microbial rennet is a coagulation factor produced by living microorganisms such as fungi, mold, or yeast. These organisms grow in a controlled laboratory environment and are monitored for the production of the right amount of fungus, mold, or yeast, and no fungi will be present in the final product. The 1970s saw a large increase in world cheese production that placed a demand on animal-type rennet beyond available supplies. As a result, it was discovered that two molds, Rhizomucor miehei and Rhizomucor pusillus, contained the active enzyme chymosin to coagulate milk. This rennet was embraced by the vegetarian community and was found to be particularly suited to soft and young cheeses. At a time when many small American farmstead cheese producers were just getting started and the price of animal rennet was increasing rapidly, the microbial version was a welcome option.
Microbial coagulants are classified into two categories:
- Thermo- stable: These coagulants are resistant to 58-59°C.
- Thermo-labile: These coagulants aren’t resistant to high temperatures.
Advantages of microbial rennet:
- Economical: Compared to animal rennet, microbial rennet is much cheaper to produce. This means that cheese production using microbial rennet has a lower production cost.
- vegetarian: This type of rennet is not taken from animals, which means that vegetarians are allowed to consume it.
- Organic: Easily available with organic labels.
- Kosher: Readily available with Kosher certification.
- Extended shelf life: Most animal rennet has a shelf life of 2-3 months; While most microbial rennet last up to 24 months.
- Easy to produce: Compared to animal rennet, these coagulants are easily produced by fermentation.
- No disease transmission: Reduces the risk of disease transmission due to the use of ruminant rennet.
- Higher proteolytic activity: The microbial coagulant is characterized by higher proteolytic activity and different properties of the substrate, and these properties may increase the ripening of the cheese.
Microbial enzymes that coagulate milk include enzyme-synthesizing bacteria and fungi.
Traditional Coagulants
The traditional coagulant is extracted from the stomach of a mammal or more usually from the fourth stomach of a calf. In the lack of commercial rennet preparations, smallholders may get the coagulant (rennin, pepsin, or chymosin) from calves, goat kids, or older fodder-eating bovines.
A crude rennet extract may be obtained from the fourth stomach (abomasum) of goat kids or calves when they are about four weeks old. Male goat kids or calves that have been fed on milk and that are not needed for breeding are usually used Young calves may not always be available so an alternative source of a milk-coagulating enzyme, pepsin, is the abomasum of adult cattle, sheep, or goats. commonly the abomasa can be obtained in plentiful supply from abattoirs.
Among different alternative coagulants applied in cheese production, aspartic proteases (APs) from flowers of thistle plants, particularly the Cynara L. genus, have gained special attention.
Thistle flowers are traditional coagulants that have been used for many years in southern Europe and northern Africa for cheese making. The flowers contain aspartic proteases (APs) with high milk-clotting and cheeses produced with the plant rennet tend to have a creamier and softer texture and more intense odor and flavor compared with those made with commercial chymosin or calf rennet.
Genetically modified (GM) Chymosin:
Advances in DNA engineering since the 1980s have made it possible to produce rennet substitutes from genetically encoded microorganisms. Scientists extract the rennet-producing genes from animal stomachs and insert them into certain bacteria, fungi, or yeast to make them produce chymosin during fermentation. The GM microorganism is killed after fermentation and chymosin is isolated from the fermentation broth so that the fermentation-produced chymosin (FPC) used by cheese producers does not contain any GM component or ingredient. Therefore, for some vegetarians, this is an issue, while for other consumers, the problem is the use of GMOs in general (Some would argue that since the original enzyme structure is not altered, this process is technically not genetic engineering). Many cheesemakers prefer GM chymosin, saying it is much more reliable and less expensive than its traditional counterpart.
