In the West, soymilk has become a popular
alternative to cow’s milk, with a roughly
similar protein and fat content, but the fat less
saturated (soy milk must be fortified with
calcium in order to be a good nutritional
substitute). But it is dilute, textureless, bland,
and not very versatile. The Chinese found two
ways to make it more interesting (and to
remove the gas-causing oligosaccharides):
coagulate the milk into surface skins, or
coagulate it into curd.
Soymilk Skin When animal or seed milks are
heated in an uncovered pot, a skin of
coagulated protein forms on the surface. The
skin forms because proteins unfolded by the
heat concentrate at the surface, get tangled up
with each other, and then lose their moisture
to the dry room air. As they dry, they get even
more tightly tangled, and form a thin but solid
protein sheet, entrapping oil droplets and
developing a fibrous, chewy texture.