About Rennet

Alternative coagulants

Due to the limited availability of proper stomachs for rennet production, cheese-makers have always looked for other ways to coagulate the milk. Only about 35% of world-wide cheese production can be done by the use of animal rennet; 65% is already done with other coagulants. Artificial coagulants are a useful alternative, especially for cheap or lower-quality cheeses.

As the proper coagulation is done by enzymatic activity, the task was to find enzymes for cleaving the casein that would result in taste and texture similar to what animal-based rennet produces.

[edit] Vegetable rennet

Many plants have coagulating properties. Some examples include fig tree bark, nettles, thistles, mallow, and Creeping Charlie. Commercial so-called vegetable rennets usually contain rennet from the mold Mucor miehei - see microbial rennet. Rennet from thistle or cynara is used in some traditional cheese production in the Mediterranean.

These real vegetable rennets are also suitable for vegetarians. Vegetable rennet might be used in the production of kosher cheeses but nearly all kosher cheeses are produced with either microbial rennet or GM rennet. Worldwide there is also no industrial production for vegetable rennet.

[edit] Microbial rennet

There are some moulds like mucor miehei that have the capability to produce proteolytic enzymes. These moulds are produced in a fermenter and then especially concentrated and purified to avoid contamination with unpleasant side products of the mould growth.

The flavour and taste of cheeses produced with microbial rennets tend towards some bitterness, especially if longer maturation is wanted. These so-called "microbial rennets" are suitable for vegetarians if there was no animal-based alimentation used during the production in the fermenter.

[edit] Genetically engineered rennet

Because of the above imperfections of microbial rennets, some big companies sought further replacements of natural rennet. With the development of genetic engineering, it suddenly became possible to use calf-genes to modify some bacteria, fungus or yeast to make them produce Chymosin. Chymosin produced by genetically modified enzymes was the first artificially produced enzyme to be registered and allowed by the FDA in the USA. In 1999, about 60% of U.S. hard cheese was made with genetically engineered Chymosin.[1]

Today the most widely-used genetic rennet is produced by the fungus Aspergillus niger. The problems of destroying the aflatoxins or the antibiotic resistant marker genes seem to be solved.

Cheese production with genetic rennet is similar to production with natural calf rennet. Genetic rennet only contains one of the known main chymosin types – either type A or type B. Some of the other chymosin types found in genetic rennet do not exist in natural rennet. This is also the reason why special analysis can determine what kind of coagulant has been used.

Often a mixture of genetic Chymosin and natural pepsin is used to imitate the complexity of natural rennet and to get the same results in coagulation and in development of flavour and taste.

The so-called "GM rennets" are suitable for vegetarians if there was no animal based alimentation used during the production in the fermenter.

[edit] Acid coagulation

Milk can also be coagulated by adding some acid, e.g. citric acid. This form of coagulation is sometimes used in cheap mozzarella production without maturation of the cheese. Paneer is also made this way. The acidification can also come from bacteria as happens in soured milk.