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the leavening used to make kefir from cow’s milk. In the dry state kefir grains, which are about the size of a hazelnut, are golden yellow, irregularly shaped, and bumpy; When placed in milk, they swell to two to five times their size. Kefir grains are native to the Caucasus, where they were used in ancient times as a leavening agent since they are a natural community of microorganisms. Kefir grains are composed of casein and several microorganisms, including Streptococcus lactis, which ferments the lactose to form lactic acid; Streptobacterium plantarum, which gives the kefir the required consistency and taste; and Torulopsis kefir, which ferments the lactose to form ethyl alcohol and carbon dioxide.