Cheese processing (part 1)

Milk is the food of the newborn. Its composition is specific to each mammal and meets the first nutritional requirements. However, sub-stitutions are possible, and in particular animal milks have been adapted to the needs of infants. It was not long before man realized that the milk produced by animals could form part of his diet. When he tried to preserve it, he came up against its fragility. In fact, its composition favors the development of numerous micro-organisms that can alter and destabilize it, causing it to change appearance. It becomes a gel, releasing a clear, yellowish liquid. In the process, the most nutritious elements are transformed under certain conditions into an acidic mass with a longer shelf-life than milk. This can evolve into products with different and varied tastes. Mastery of these transformations leads to what we now call cheese.

Gradually, processing techniques developed, often around regional practices guided by the nature of the milk available, dietary habits and the socio-cultural context. The accumulation of knowledge in the science of milk and the mastery of processing techniques mean that today there are many varieties of cheese, each with its own unique character. In order to compare them or to facilitate trade, it is customary to classify them into broad categories according to various criteria such as animal species, water content, degree of ripening, type of crusting, visible mould, texture and manufacturing techniques. Different classifications exist, depending on the order and importance attached to the selection criteria.

Today, processing milk into cheese has become an important economic activity. Cheese is the main form of milk consumption in France. In 1999, cheese processing (ex-factory value) accounted for 43% of the total value of milk produced, while 34% of milk collected was processed into cheese [1] . In the same year, 1,685,425 tonnes of cheese were produced, 94.3% from cow's milk, 3.3% from goat's milk and 2.9% from ewe's milk [1] . This cheese production is equivalent to 25% of European production (EU15).

The quantities of cheese produced vary greatly from one type of cheese to another. Differences are sometimes measured by factors greater than 1,000. However, three major classes of similar size share production: 34% of total cheese production for fresh cheeses, 30% for soft cheeses and 32% for all pressed and pressed-cooked cheeses.

In order to achieve the organoleptic quality and consistency of composition and presentation we have come to expect, we need a thorough understanding of the various stages in the transformation of milk...