In the preparation of kefir the milk should be fresh, and a better product is made if it be skimmed and sterilized so that the fermentation when finished will be kefir grains alone. A richer product in alcohol is also secured if some additional milk and sugar are added before fermentation.

Further information regarding koumys is found in "Foods and Their Adulterations," 3d edition, pages 170-80. Yoghurt is a fermented milk produced by the action of the bacillus bul-garicus..