Formation of curd from milk is which reaction?

Curd formation from milk is an example of a coagulation reaction.

When milk is soured, the lactic acid produced by bacteria causes the milk proteins to coagulate, forming a semi-solid gel called curd. The curd traps the fat and other solids in the milk, while the liquid whey is released.

Cheesemaking is a process of separating curd from whey. The curd is then pressed into molds to form cheese.