On Food and Cooking

different kinds of curd structures — acid a
fine, fragile gel, rennet a coarse but robust,
rubbery one — so their relative contributions,
and how quickly they act, help determine the
ultimate texture of the cheese. In a
predominantly acid coagulation, the curd
forms over the course of many hours, is
relatively soft and weak, and has to be
handled gently, so it retains much of its
moisture. This is how fresh cheeses and small,
surface-ripened goat cheeses begin. In a
predominantly rennet coagulation, the curd
forms in less than an hour, is quite firm, and
can be cut into pieces the size of a wheat grain
to extract large amounts of whey. This is how
large semihard and hard cheeses begin, from
Cheddar and Gouda to Emmental and
Parmesan. Cheeses of moderate size and
moisture content are curdled with a moderate
amount of rennet.