Kephir and Koumiss are liquors much used in the Orient which are made from milk that has undergone alcoholic fermentation. Koumiss was originally made from mare's milk but is now often made from cows' milk by adding cane sugar and yeast. In addition to the CO_{2} developed, alcohol, lactic acid, and casein-dissolving ferments are formed. Kephir is made by adding to milk Kephir grains, which are a mass of yeast and bacterial cells. The yeasts produce alcohol and CO_{2} while the bacteria change the casein of milk, rendering it more digestible. These beverages are frequently recommended to persons who seem to be unable to digest raw milk readily. The exact nature of the changes produced are not yet well understood.[66] ~Bitter milk.~ The presence of bitter substances in milk may be ascribed to a variety of causes. A number of plants, such as lupines, ragweed and chicory, possess the property of affecting milk when the same are consumed by animals. At certain stages in lactation, a bitter salty taste is occasionally to be noted that is peculiar to individual animals. A considerable number of cases of bitter milk have, however, been traced to bacterial origin. For a number of years the bitter fermentation of milk was thought to be associated with the butyric fermentation, but Weigmann[67] showed that the two conditions were not dependent upon each other. He found that the organism which produced the bitter taste acted upon the casein. Conn[68] observed a coccus form in bitter cream that was able to impart a bitter flavor to milk. Sometimes a bitter condition does not develop in the milk, but may appear later in the milk products, as in the case of a micrococcus which Freudenreich[69] found in cheese. Harrison[70] has traced a common bitter condition in Canadian milk to a milk-sugar splitting yeast, _Torula amara_ which not only grows rapidly in milk but produces an undesirable bitterness in cheddar cheese. Cream ripened at low temperatures not infrequently develops a bitter flavor, showing that the optimum temperature for this type of fermentation is below the typical lactic acid change. Milk that has been heated often develops a bitter condition. The explanation of this is that the bacteria producing the bitter substances usually possess endospores, and that while the boiling or sterilizing of milk easily kills the lactic acid germs, these forms on account of their greater resisting powers are not destroyed by the heat. ~Soapy milk:~ A soapy flavor in milk was traced by Weigmann and Zirn[71] to a specific bacillus, _B. lactis saponacei_, that they found gained access to the milk in one case from the bedding and in another instance from hay. A similar outbreak has been reported in this country,[72] due to a germ acting on the casein and albumen.