Even after lengthy boiling, soybeans remain quite
tough and a little bitter. More importantly, due to a digestive
enzyme called trypsin which interferes with protein digestion,
soybeans are largely indigestible even after cooking. Most of the
bean's highly valuable protein just passes through your system.
No doubt it is for these reasons that the Chinese learned to process
the bean in other ways before cooking and consuming. These processes
include pressing oil from the beans, grinding and boiling to make
soy milk, grinding, boiling and adding a coagulating agent to make
tofu, and fermenting to create products like soy sauce and black
beans. Whole fresh beans (ripe beans picked before they are dry
and hard) are cooked in their pods and eaten as a vegetable.