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Animal rennet: what it is and how it works

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Introduction

When we talk about rennetwe usually refer to all those coagulants that are added to milk to obtain curd and produce cheese. In fact, the only coagulant to deserve the name rennet is that of animal derivationalso called presame.

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 wild thistle or from the green parts of the fig tree. Vegetable coagulants are used to produce goat's cheese, soft cheese or yoghurt, also suitable for those who have chosen a vegetarian diet.
  • Another option for making curd is to use the microbial coagulant, made up of proteolytic enzymes extracted from some types of mold or fungi. This type of rennet is responsible for a lower production yield and gives the cheese a more bitter taste. It is found mainly in industrially produced cheeses.
  • A third way is offered by coagulant obtained from fermentation by genetically modified microorganisms (FPC). It is a substance containing a single enzyme, genetic chymosin, obtained by modifying the DNA of some bacteria. In Italy its use is prohibited for PDO and BIO cheeses.

To know more:
Vegetable rennet and animal rennet

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 milk. There smile it 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, as it is no longer soluble, sinks to the bottom. The curd can thus be collected and processed to give rise to cheese. The watery part of milk, called serumhowever, remains in suspension and is mainly used for the creation of ricotta.

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

Pepsin also coagulates milk, but in a less specific way than chymosin: its proteolytic power is much higher, but it is less selective, that is, it acts on a greater number of proteins and not just on k-caseins. It promotes rapid ripening of the cheese, giving more flavor and taste to the curd.

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

How rennet works: coagulation process

Rennet-induced milk coagulation it is said rennet coagulation, to differentiate it from the acidic one which, instead, occurs through the addition of lactic ferments.

The rennet coagulation it has a rapid coagulation time (10 min), the resulting curd has a good consistency and is uniform and elastic. It is used for DOP brand 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 temperature, the rennet coagulation process requires a range between 30-42 °C depending on whether it is soft or hard cheese.

The acid coagulation occurs through the lowering of the pH and involves the use of natural lactic ferments from milk or inoculated by the cheesemaker. The coagulation time is longer than 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 goat's cheese.

The role of cheeses in diets

Il cheese it is one of the great protagonists of the Italian table. An excellence is represented by DOP cheesesproducts of curdamong which we include Grana Padano, Buffalo Mozzarella from Campania, Parmigiano Reggiano, Pecorino Romano. The importance of cheeses in nutrition is linked to their nutritional properties.

Cheese is a concentrate of nutrients, rich in proteins with high biological value due to the content of essential amino acids. Cheese, moreover, is a primary source of vitaminsin particular those of group B including B12 and B2, vitamin A and vitamin D. Furthermore, it provides our body essential mineral salts for the correct development of bone during growth as calcium and phosphorus and also provide 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, in particular cholesterol, so doses of 50 grams of cheese per meal should not be exceeded if they are mature fatty cheeses.

Where is the rennet extracted from?

Rennet is obtained from the fourth stomach or abomasum of some suckling ruminant animals such as calf, buffalo, lamb or kid. Young ruminants are chosen because by feeding only on their mother's milk they have a greater enzymatic richness in their abomas both in terms of composition and coagulant activity. There is a higher percentage of chymosin than pepsin, percentages which will be different depending on the extraction abomasum. Instead, the change in diet of adult cattle now weaned 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.

Conclusion

In recent years, coagulants of plant origin have become increasingly popular on the market, being easy-to-use and less expensive products. 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, rennet, together with milk and salt, still remains the secret to a high-quality final product and the abomasum from which it is extracted will give the flavour, smell and uniqueness to each cheese.

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