Kefir comes from high in the Caucasus a 750-mile-long mountain range between the Caspian and Black seas. Today, it’s commonly produced from cow’s milk. It’s a slightly sour brew of fermented milk, most of which contains about 2 1/2 percent alcohol. Kefir is reminiscent in both taste and texture of a liquid yogurt. It’s available in cartons or bottles in health-food stores. See also kumiss.