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Rennet is a natural coagulant of choice of milk.


Rennet is mainly composed of two enzymes in combination: 80% chymosin and 20% pepsin. Enzymes are  naturally present in the 4th stomach of young ruminants, or abomasum.

Rennet (either as abomasum, either as liquid or powder preparation) is used to curdle milk for millennia.

France, land of cheese remains one of the only countries in the world using still mostly this type of coagulant preparation.


Moreover, it is recognised that at the same enzyme concentration, there are significant differences, depending on their mode of production and their origin, among the various rennet proposed to cheese makers.

The rennet obtained by an extraction process by slow maceration (several days of maceration) allows producing better quality cheese compared to rennet from fast extraction processes (few hours)




In the 1970s, for fear of shortage of abomasum, and therefore rennet, research laboratories have managed to extract the coagulant enzymes from fungi (Mucor miehei, Mucor pusillus) and/or parasites (Cryphonectria parasitica). If these coagulant enzymes coagulate milk, cheese results are often average or poor: lower cheese yield, bitterness in cheese, bad ageing, etc ... and therefore do not allow to obtain quality cheeses equivalent to those obtained with a good traditional rennet, despite improvements in these enzymes in the past decades.




In the 1990s, for economic and financial reasons, and again in the eventuality of a potential shortage of stomachs (often speculative), a new generation of coagulating enzymes: appeared: the fermentation chymosins genetic engineering. To do this, a molecule of chymosin from calf rennet was cloned into bacteria. These genetically modified bacteria were multiplied in order to extract the chymosin proteins thus duplicated. Today, these chymosins are widely used worldwide to coagulate the milk. Producers, foreign multinationals, have obtained international authorities that the use of these genetically engineered chymosins is not indicated on the cheese. It is estimated that over 40% of global cheese production are made with this type of enzyme. In France, to date nearly 30% of cheeses contain it! Only cheeses of Protected Designation of Origin, under label, farmers or BIO by their respective specifications must use rennet.

As a guide, Switzerland assimilates products derived from GMOs to GMOs, and therefore, requires that their use is clearly indicated to the attention of consumers.

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