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Rennet (also calf rennet , cheese stomach ) is a mixture of the enzymes chymosin and pepsin , which is obtained from the abomasum of young ruminants of milk- drinking age and is used to precipitate milk protein in the production of cheese .

Above all, chymosin naturally serves to make breast milk digestible by thickening it. Every mammal produces a special form of chymosin in its stomach in order to precipitate the milk protein - casein - in the stomach and thus make it digestible. In humans, this enzyme is called chymotrypsin and is produced by the pancreas.

Every cheese that is produced by means of sweet milk curdling (hence the name sweet milk cheese ) requires rennet or rennet substitute as an additive to coagulate the milk. Almost all known types of hard and semi-hard cheese come from curdling sweet milk. Also cream cheese of the typically by sour milk coagulation with the aid of, lactic acid bacteria of quark or yoghurt is prepared may contain Lab.

The ability of rennet to break down the milk protein casein in such a way that the milk thickens without becoming sour was recognized in ancient times and made usable for cheese production. For example, Aristotle praises the rennet of young deer or roe deer as being particularly effective.


The enzyme contained in the rennet causes very large quantities (1: 6000–1: 600,000 parts) of milk to coagulate even in small doses . It is most effective at 36–37 ° C, but loses its power very quickly at higher temperatures. A weakly acidic reaction favors the rennet effect, alkaline ones and certain salts counteract it. The coagulation effect of the rennet is due to the cleavage of a part ( glycomacropeptide ) of the casein micelle (more precisely: κ-casein) by the chymosin . As a result, the micelles lose their “protective shell” and the micelles aggregate , which ultimately leads to gel formation. The gel is after its formation essentially of a solid phase, the protein network, and the enclosed therein sweet whey . The rennet only acts as a catalyst , so it is not used up in the cleavage reaction. Therefore, even very small amounts are sufficient to curdle the milk. A larger amount of rennet and increased temperatures increase the reaction rate and thus change the structure of the gel that forms. The reaction comes to a standstill after a while because the substrate is consumed ( enzyme reaction). The reaction can only be terminated by inactivating the enzyme, for example with heat, acid, lye, etc. This is not necessary in cheese production and would also lead to considerable changes in the resulting cheese. After the gel has been cut into the cheese curd , part of the sweet whey escapes from the gel network during syneresis . The dry mass of the resulting cheese can be controlled via the temperature, size of the broken cubes / broken grains and the duration of the syneresis. Soft cheese is obtained with low temperature and large broken grains, hard cheese with high temperature and small broken grains .

In practice, the rennet is usually used for cheese preparation at temperatures between 30 and 36 ° C - the optimum temperature for the enzyme is body temperature, the optimum for the cheese-making process is slightly lower. At temperatures below 30 ° C, there is usually no or poor coagulation.


Lab is internationally classified as a production aid and not as a food additive . Therefore, the type of coagulant used (rennet) does not have to be declared. Normally, therefore, no information about the origin of the rennet is given on the packaging. In organic supermarkets and vegetarian shops , it is now almost always indicated whether animal rennet or one of the substitutes was used. In organic cheeses, the use of rennet substitutes that are obtained with the help of white biotechnology is expressly prohibited in any case .


Respiratory allergies can develop to the components of rennet, especially in the event of occupational exposure.


Alexander Schmidt (1831-1914) and Olof Hammarsten (1841-1932) found out in 1871/1872 that the rennet was responsible for the coagulation of milk. The conversion of the casein is still independent of calcium, but it is required in the next step, the precipitation. Maurice Arthus and Calixte Pagès (born 1857) were also able to confirm this influence of calcium .

It has long been assumed that chymosin and pepsin are an enzyme. However , through their research, Olof Hammarsten and Sigval Schmidt-Nielsens (1877–1956) were able to prove that the rennet is an independent enzyme, which was isolated for the first time in 1942.

Production of natural rennet (animal rennet)

Animal rennet - natural rennet - is produced in the so-called main cells of the gastric mucous membrane of the fourth stomach ( abomasum ) of young ruminants who are still suckling milk for milk digestion and then secreted by these cells when required . Rennet from calves is mostly used for cow's milk, but it can also come from sheep and goats . Rennet from other mammals - with the exception of camel rennet for camel milk - is not used. The younger the animal from which the stomach originated and the less food other than milk it consumed, the higher the chymosin content and the better the rennet quality.

Every mammal produces its own special rennet enzyme to digest breast milk. Therefore, calf rennet is best suited for cheese production from cow's milk.

Every form of natural rennet production aims only at transferring the enzyme produced in the main cells of the gastric mucosa into an extraction solution. Stomachs for rennet production are specially prepared at high cost, frozen or preserved with salt.

Classic production methods

Today this production method is only used by very traditional alpine dairies. To prepare a rennet of great strength and durability, cut the dried stomachs of suckling calves at least three months old, from which the wrinkled part has been separated, into small pieces and leave 100 parts of them with 1 liter of water, 50 g of table salt and 40 g of boric acid Stand at normal temperature for five days with frequent shaking, then add another 50 g of table salt and filter . 1 part of good rennet liquid must curdle at least 6000 parts of fresh whole milk at 35 ° C in 40 minutes.

A rennet essence suitable for whey preparation ( Liquor seriparus ) is obtained by macerating 3 parts of freshly scraped abomasum mucous membrane with 26 parts of wide (very slightly acidic, 8 to 9 percent alcohol containing) wine and one part of table salt for three days . A teaspoon full of the filtrate, heated to 35 to 40 ° C, causes 0.5 liters of milk to curdle.

Modern method

In modern dairy farms - especially in New Zealand, Australia, but also the USA and Canada - the newborn calves are separated from the suckler cow after 2 to 10 days, slaughtered and processed. In addition to many other recycling products, including feed for pets, the abomasum are specially prepared, deep-frozen and sold to rennet producers.

The frozen abomasum are chopped up and the rennet enzyme is extracted from it in an extraction solution. The solution is then freed from all impurities in several filtration stages. The enzyme is activated, concentrated and preserved in a saline solution.

In further processing steps, chymosin and pepsin can also be precipitated from the rennet extract and processed into a rennet powder. Rennet powder has a higher concentration than an extract.

1 kilogram of rennet extract contains approx. 1 gram of pure enzyme substance, the rest is water and salt. Approximately 200 grams of rennet extract (depending on the concentration of the rennet extract) are required to produce approx. 100 kg of cheese. During the cheese making process, depending on the type of cheese and processing, 60 to 80% of the rennet enzyme is washed out with the whey. This means that only about 0.0004 to 0.0008 grams of rennet enzyme remain in one kilogram of cheese - corresponds to 0.4 to 0.8 ppm (parts per million).

Rennet substitutes

The number of calf stomachs for the extraction of natural rennet is determined by the demand for veal and is therefore limited. Global cheese production increases annually. Only about 35% of the world's cheese production can be produced with natural rennet. Alternative coagulants must be used for the remaining 65%. Vegetarians see natural rennet as unsuitable for cheese production because the enzyme is extracted from calf stomachs. In Islamic communities, natural rennet is used for cheese production, but it must be halāl -certified - the raw material must come from animals slaughtered according to the Islamic rite. Production must also be controlled and certified. The Jewish dietary laws exclude the use of natural rennet, since when using animal rennet, the prescribed separation of milk and meat is not observed.

Vegetable rennet substitutes

Enzymes that have a very similar effect to rennet are mainly found in rennet herbs , which is what gave this genus its name. Further occurrences in the plant kingdom are: sap of papaya , milk sap of fig tree , sap of pineapple or the proteases purified from them papain , ficain and bromelain . Vegetable coagulants, however, produce atypical and unusual taste results in cheese and are traditionally only used with special types of cheese in some countries, such as B. Portugal (the thistle-like plant Cynara cardunculus in the Queijo Serra da Estrela ) or England (the real bedstraw Galium verum in the Double Gloucester ).

Microbial rennet substitutes

Today rennet-like proteases - Mucor-Pepsins - can also be produced microbially in fermenters . Molds (lat. Mucor ) ( Rhizomucor miehei (formerly Mucor mihei )), Rhizomucor pusillus (formerly Mucor pusillus or Endothia parasitica ) are used as producers for the rennet substitutes . Due to the different amino acid composition , the production process for the cheese must be adapted. Bitter peptides can develop in cheese that ripens longer. The latest research also shows that cheese losses can occur. The microbial products are also often incorrectly referred to as vegetable rennet. When using suitable nutrient media in the fermenter - z. B. no blood - albumin for the supply of amino acids - these products are suitable for vegetarian cheese. The EFSA denied in a statement in particular fungi, which are mainly used for the production of microbial rennet fabric, the QPS (Qualified Presumption of Safety).

Biotechnologically produced rennet substitutes

An alternative to natural rennet enzymes is chymosin , which is produced with the help of genetically modified microorganisms ( Escherichia coli (bacterium), Kluyveromyces lactis ( yeast ) or Aspergillus niger ( mold )). In Switzerland , approval was granted in 1988 by the Federal Office of Public Health . There is no obligation to declare that the cheeses produced in this way are considered GM-free and are therefore not counted as genetically modified foods . In Germany, three chymosin rennet substitutes (under the trademarks Maxiren, Chymogen or Chy-Max) are currently approved. In contrast to calf rennet with 3 main types of chymosin and at least 3 sub-types as well as the corresponding pepsins, these products only contain a single type of chymosin - either A or B - which, however, is identical in amino acid composition to the respective natural chymosin type. These enzymes break down more specifically, which leads to an increased yield and a reduced bitter taste compared to natural rennet and microbial substitutes. These products are banned in Europe for the production of organic food . For vegetarian cheeses, these products are ideal when using suitable nutrient media in the fermenter - e.g. B. no albumin to supply amino acids  - suitable.

Individual evidence

  1. A. Kumar, S. Grover, J. Sharma, VK Batish: Chymosin and other milk coagulants: sources and biotechnological interventions. In: Critical reviews in biotechnology. Volume 30, Number 4, December 2010, pp. 243-258, ISSN  1549-7801 . doi: 10.3109 / 07388551.2010.483459 . PMID 20524840 .
  2. G. Bittante, M. Penasa, A. Cecchinato: Invited review: Genetics and modeling of milk coagulation properties. In: Journal of dairy science. Volume 95, Number 12, December 2012, pp. 6843-6870, ISSN  1525-3198 . doi: 10.3168 / jds.2012-5507 . PMID 23021752 .
  3. Käselab ,
  4. ^ Van Kampen, V .: Occupational Allergies against Pepsin, Chymosin and Microbial Rennet , Pneumologie 5, 67, 2013 Thieme.
  5. ^ A b c Wolf-Dieter Müller-Jahncke , Christoph Friedrich , Ulrich Meyer: Medicinal history . 2nd, revised and expanded edition. Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, ISBN 978-3-8047-2113-5 , p. 114 .
  6. What is kosher?
  7. Klaus Lösche: Enzymes in food technology. Behr's Verlag DE, 2000, ISBN 978-3-86022-640-7 , p. 47.
  8. ^ Oxford University Press: The Oxford Companion to Cheese. Oxford University Press, 2016, ISBN 978-0-19-933090-4 .
  9. Peter Lund Simmonds: The Commercial Dictionary of Trade Products, Manufacturing and Technical Terms .... G. Routledge and Sons, 1872, p. 84.
  10. Kassensturz : Gentech 1/2 In: ( video on December 5, 1995), accessed on October 6, 2018.
  11. Claudia Hoffmann: Green genetic engineering is conquering the world - five things you should know In: , November 4, 2016, accessed on October 6, 2018.
  12. rennet chymosin ( "Chymogen", "Chy-Max" or "Maxiren"). To No. 1997-003-00 , BVL

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