Animal rennet: how it works and where it comes from

Animal rennet: how it works and where it comes from


When we talk about rennet , we usually refer to all those coagulants that are added to the milk to obtain the curd and to produce the cheese . Actually, the only coagulant that deserves the name of rennet is that of animal origin , also called rennet .

In addition to animal rennet, there are others capable of promoting coagulation.

  • One of them is the vegetable coagulant , which is extracted from the flowers of the thistle or the green parts of the fig tree . Vegetable coagulants are used to make goat’s cheese , soft cheese or yoghurt , also suitable for those who have chosen a vegetarian diet .
  • Another possibility to produce the curd is to use the microbial coagulant, consisting of proteolytic enzymes extracted from some types of molds or fungi. This type of rennet is responsible for a lower production yield and gives the cheese a more bitter taste. It is mostly found in industrially produced cheeses.
  • A third way is offered by the coagulant obtained from fermentation by genetically modified microorganisms (FPC). It is a substance containing only one enzyme, genetic chymosin, obtained by modifying the DNA of some bacteria . In Italy it is forbidden to use it for PDO and BIO cheeses.

    Animal rennet. What is it?

    Rennet is a natural enzymatic complex, of which chymosin is the main constituent and the main enzyme responsible for coagulating the milk. Chymosin is a very selective protease and coagulates only some milk proteins , the k- caseins , which precipitate thus forming the curd . This is a gelatinous protein mass rich in proteins, fats, vitamins and mineral salts which, being no longer soluble, sinks to the bottom. The curd can thus be collected and processed to give rise to cheese . The aqueous part of the milk, called whey , instead remains in suspension and is mainly used for the realization of thecottage cheese .

    The other enzymes in rennet are pepsin (an acid protease) and, only in kid or lamb rennet paste , lipases .

    Pepsin also makes milk coagulate, but in a less specific way than chymosin: its proteolytic power is much higher , but it is less selective, i.e. it acts on a greater number of proteins and not only on k-caseins. It favors a rapid maturation of the cheese, giving more flavor and taste to the curd.

    Lipases are pre-gastric enzymes, which do not degrade proteins but act on fats. Lipases enrich the taste and flavor of the cheese and, by reducing the maturing times, increase the efficiency of the production process.

    How rennet works: coagulation process

    The coagulation of milk induced by rennet is called rennet coagulation , to differentiate it from the acidic one which, instead, occurs by adding lactic ferments .

    Rennet coagulation has a rapid coagulation time (10 min), the resulting curd has a good consistency and is uniform and elastic. It is used for DOP branded cheeses (such as Grana Padano , Parmigiano Reggiano and Pecorino Romano ), but also for other types of dairy products. Since the activity of the rennet is influenced by the temperature, the rennet coagulation process requires a range between 30-42 °C depending on whether it is a soft or hard cheese.

    Acid coagulation takes  place through the lowering of the pH and involves the use of natural lactic ferments in the milk or inoculated by the cheesemaker. The coagulation time is longer than the rennet coagulation, lasting even over 24 hours, but it takes place at lower temperatures. The curd produced is not very consistent and crumbles easily. It is used for the production of some fresh cheeses , such as goats.

    The role of cheeses in diets

    Cheese is one of the great protagonists of the Italian table. An excellence is represented by DOP cheeses , curd products , among which we include Grana Padano, Mozzarella di Bufala Campana, Parmigiano Reggiano, Pecorino Romano. The importance of cheeses in food is linked to their nutritional properties.

    Cheese is a concentrate of nutrients , rich in proteins with a high biological value due to the content of essential amino acids . Furthermore, cheese is a primary source of vitamins , especially those of group B including B12 and B2, vitamin A and vitamin D. In addition it provides our body with essential mineral salts for the correct development of bones during growth such as calcium and phosphorus and also bring magnesium and zinc .

    However, we must be careful to include them in our diet in a balanced way . They have a high salt content , which is often added during processing and are rich in fats, especially cholesterol , so you shouldn’t exceed 50 grams of cheese per meal in the case of mature fat cheeses .

    Where is the rennet extracted from?

    The rennet is obtained from the IV stomach or abomasum of some suckling ruminant animals such as veal , buffalo, lamb or kid. Young ruminants are chosen because, feeding only on mother’s milk, they have a greater enzyme richness in their abomas both in terms of composition and coagulant activity. A higher percentage of chymosin is found compared to pepsin, percentages which will be different according to the extraction abomasum. On the other hand, the change in diet of the now weaned adult cattle reduces the enzymatic richness of the fourth stomach, bringing the ratio between chymosin and pepsin in favor of pepsin. This results in a lower dairy yield.


    In recent years, plant-based coagulants have increasingly gained ground on the market, being products that are easy to use and less expensive. They represent a good substitute for animal rennet, meeting the requests of vegetarians or the needs of those who, for ethical or religious reasons, choose an alternative coagulant.

    Nonetheless, the rennet, together with the milk and salt, still remains the secret for a high quality final product and the abomasum from which it is extracted will give each cheese its flavour, smell and uniqueness.



Leave a Reply

Your email address will not be published. Required fields are marked *