On Food and Cooking

ricotta, and most fresh goat cheeses; all of
them are curdled exclusively or primarily by
means of acid, not rennet. Rennet creates a
malleable structure of large casein micelles
held together by relatively few calcium atoms
and hydrophobic bonds, so this structure is
readily weakened by heat. Acid, on the other
hand, dissolves the calcium glue that holds the
casein proteins together in micelles (p. 20),
and it eliminates each protein’s negative
electrical charge, which would otherwise
cause the proteins to repel each other. The
proteins are free to flock together and bond
extensively into microscopic clumps. So when
an acid curd is heated, the first thing to be
shaken loose is not the proteins, but water: the
water boils away, and this simply dries out
and concentrates the protein even further. This
is why firm paneer and queso blanco can be
simmered or fried like meat, and goat cheeses
and ricotta maintain their shape on pizzas or
in pasta stuffings.