Kefir (alternately keefir, kephir, kewra, talai, mudu kekiya, milkkefir, búlgaros) is a fermented milk drink that originated in the Caucasus region. It is prepared by inoculating cow, goat, or sheep's milk with kefir grains. Traditional kefir was made in skin bags that were hung near a doorway; the bag would be knocked by anyone passing through the doorway to help keep the milk and kefir grains well mixed.