ALCOHOLIC FERMENTATION 195 



The alcoholic fermentation does not occur normally in 

 milk, because lactose, the sn-<ir in milk, is not readily sus- 

 ceptible to fermentation. Also, the extent of seeding with 

 yeasts is not sufficient to enable fermentative changes to 

 develop rapidly. As a consequence, the activity of the 

 yeasts is usually overshadowed by bacterial changes. 

 While most yeasts are unable to act on milk-sugar, yet 

 lactose-fermenting yeasts do occur not infrequently, and 

 are often to be noted in milk if it is held for some time 

 after it has become sour. The soured milk will contain 

 an abundance of sugar, and the acid will prove no de- 

 terrent to yeast growth. Yeast development occurs in milk 

 and cream held for considerable periods. Cream supplied 

 to large central i/ed creameries often shows a yeasty fer- 

 mentation. An alcoholic fermentation is also noted in 

 cheese factories, especially in the whey-tanks, on account 

 of the favorable opportunity for contamination and growth 

 <>f yeasts. 



When such fermented whey is returned to the farm in 

 milk-cans and these are imperfectly washed, the fresh milk 

 may become seeded to such an extent as to cause abnormal 

 ferment at ions in the cheese, injuring its commercial value. 

 This is particularly true of Swiss cheese, in which the de- 

 velopment of acid in the process of making is not carried 

 sufficiently far to transform all of the sugar into acid. 



Certain kinds of fermented milks are also prepared by 

 the use of lactose-fermenting yeasts. When raw milk is 

 used, the milk will be subject to both the acid and the alco- 

 holic fermentations, and the taste of the acid milk will be 

 modified by that of the alcohol. Two of these fermented 

 milks are widely used in eastern Europe and western Asia. 

 Koumiss is prepared from mare's milk by the nomadic 

 peoples of the Caucasus. The fresh milk is inoculated with 

 a little of the previously fermented milk, which may be 



