FERMENTATION OF CARBOHYDRATES 



85 



the "strong" odor of certain kinds of cheese is due to this 

 acid, which is formed partly from the milk-sugar remaining 

 in the cheese. Most of it under these conditions comes from 

 the proteins of the cheese and especially from the fat (see 

 page 87). 



Fig. 60. — 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 oxidizes the alcohol to acetic acid. The vinegar is drawn off below. 



As has been indicated alcohol is a common accompani- 

 ment 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- 

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

 In brewing and distilling industries, yeasts are used to make 



