This is one of the most important phases of cheese production. The main protein in milk, casein, hardens to produce a coagulated mass called curd. Coagulation can be induced through acidification or through the addition of rennet (enzymatic coagulation).
Acid coagulation occurs thanks to certain lactic bacteria that develop naturally (or are specially introduced) in order to acidify the milk. The coagulated mass is crumbly and not particularly firm, with low calcium levels and a lot of internal serum. This process is widely used in the preparation of fresh cheeses such as goat’s cheese.
Enzymatic coagulation involves the addition of rennet. The curd produced with rennet is firm, elastic and rich in calcium and is used for most cheeses.