CHAPTER XLIX 



VIN EGA B-MAKING 



The transformation of sugar into alcohol by yeasts 

 and other microorganisms opens the way for still other 

 changes. Apart from the various bacteriological diseases 

 of alcoholic beverages already noted, the alcohol itself 

 is the raw material for the preparation of acetic acid. 

 It is well known that when wine, beer, or cider are left 

 to themselves, they are likely to turn sour in the course 

 of time; that is, they are likely to change into vinegar. 

 Vinegar is, therefore, a sour liquid containing variable 

 quantities of acetic acid made out of alcohol. 



History of the art. — Old as is the art of vinegar-mak- 

 ing, the true nature of the processes involved was not 

 even suspected in the early days of the last century. 

 In 1837, Kiitzing expressed the belief that the change 

 of alcohol into vinegar is accomplished by living organ- 

 isms. His statement was not accepted, however, as the 

 true explanation of the phenomenon. The chemists, 

 led by Liebig, carried the day, and it came to be believed 

 for a time that the formation of acetic acid is a purely 

 chemical process. 



This claim was supported by the discovery made by 

 Davy in 1821, that when alcohol is poured on platinum- 

 black the latter becomes very hot and transforms the 



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