As will have been noticed, it is an essential part of the process of koumiss-making to keep the milk in a state of agitation during the period of fermentation, a process which is intended to permit of oxygen being taken up by the fermenting fluid, while, at the same time, the casein is broken up into a state of fine division. The casein also, or at least a portion of it, becomes very soluble, and after twelve hours of fermentation the taste of the product is only slightly sour, and the milk taste still remains. This taste, however, disappears in twenty-four hours, owing to the rapid development of the lactic acid organisms. After this lapse of time the sugar is entirely destroyed, and the strong koumiss which results is a thin sour fluid which effervesces briskly, and in this condition will keep for an indefinite period. "The net change which has taken place in the original milk may be summed up by saying that the sugar of the milk has been replaced by lactic acid, alcohol, and carbon dioxide, the casein has been partly precipitated in a state of very fine division, and partly pre-digested and dissolved, while the fat and salts have been left much as they were."[24] Violent stirring or agitation of the cultures does not seem to work so much by supplying oxygen to the fermenting liquid, as by ensuring a thorough distribution of the micro-organisms throughout the liquid, and thus dividing the casein. The greater number of the organisms are facultative anærobes and oxygen is not necessary. Again, koumiss put up in bottles on the first day is regularly shaken although air is excluded.