FERMENTATION OF CARBOHYDRATES 89 



As has been indicated alcohol is a common accom- 

 paniment of most acid fermentations, as are the esters of 

 acids other than the chief product. Bacteria are not used 

 in a commercial way to produce alcohol, however, as the 

 yield is too small. There are some few bacteria in which 

 the amount of alcohol is prominent enough to call the pro- 



FiG. 66. — A vinegar ripener. The tank shown opened at the side is filled 

 with a special type of beech shavings which thus provide a very large surface. 

 The apple juice which has been previously fermented with yeast, which 

 converts the sugar into alcohol, is allowed to trickle through the openings 

 at the top over the shavings. The acetic acid bacteria on the shavings 

 rapidly oxidize the alcohol to acetic acid. The vinegar is drawn off below. 



cess an "alcoholic fermentation" rather than an acid one. 

 In brewing and distilling industries, yeasts are used to make 

 the alcohol, though molds replace them in some countries 

 ("sake" and "arrak" from rice). 



Under ordinary conditions the carbohydrate is never com- 

 pletely fermented, since the accumulation of the product — 



