enzyme, called chymosin, in a bacterium, a
mold, and a yeast. Today, most cheese in the
United States is made with these engineered
“vegetable rennets,” and less than a quarter
with traditional rennet from calf stomach
(which is often required for traditional
European cheeses).
The curdling of milk by the rennet enzyme
chymosin. The bundled micelles of casein in
milk are kept separate from each other by
electrically charged micelle components that
repel each other (left). Chymosin selectively
trims away these charged kappa-caseins, and
the now uncharged micelles bond to each
other to form a continuous meshwork (right).
The liquid milk coagulates into a moist solid.