Yogurt is a food produced by bacterial fermentation of milk. The
bacteria used to make yogurt are known as yogurt cultures. Fermentation
of sugars in the milk by these bacteria produces lactic acid, which acts
on milk protein to give yogurt its texture and characteristic tart
flavor. Cow's milk is the milk most commonly used to make yogurt. Milk
from water buffalo, goats, ewes, mares, camels, and yaks are also used
to produce yogurt. The milk used may be homogenized or not. It may be
pasteurized or raw. Each type of milk produces substantially different
results.