FERMENTATION OF CARBOHYDRATES 191 



sugar solution with a suitable type of yeast and small quan- 

 tities of lactic acid bacteria. Usually air is bubbled through 

 the fermenting mixture. The yeasts multiply rapidly. 

 They are removed from the liquid in which they are grow- 

 ing, either by sedimentation or by centrifugation in a 

 machine somewhat resembling a milk separator. The yeast 

 cells are then washed, again separated and pressed into 

 cakes. In the so-called compressed yeast a comparatively 

 small amount of starch will be present. In the dried yeast 

 cakes the yeast is mixed with corn meal, or similar absorb- 

 ent material, pressed into cakes and dried. 



Development of Fusel Oils in Alcoholic Fermentation. 

 Important by-products in alcoholic fermentation are the 

 fusel oils, consisting primarily of isoamyl alcohol. Formerly 

 it was supposed that these were derived from the sugar, but 

 more recent study has shown these to be derived -from the 

 amino acids developed from the digestion of proteins. Iso- 

 amyl alcohol is developed from isoleucine. 



