Essentially, cheesemaking comprises five stages. First the milk is acidified, or soured, by warming it and introducing a starter culture, and when the correct acidity has been reached rennet (or a vegetarian equivalent) is added; this coagulates the milk, separating it into solid curds and liquid whey. Then the curd is cut, or broken up, and drained. The fineness of the cut affects the amount of whey left in the cheese which in turn determines its character. Fresh soft cheeses are cut sparingly, but hard cheeses are cut into very tiny pieces. With extra-hard cheeses the curd is “cooked”; this shrinks it, making it easier to extract the maximum moisture.