ACETIC FERMENTATION 213 



cells are usually oval, sometimes elongated or pickle-shaped. 

 Usually they occur in pairs though sometimes they are 

 united into chains of different lengths. This organism 

 develops rapidly upon the shavings used in the quick vine- 

 gar process and is very active in the oxidation of alcohol to 

 acetic acid. As much as 11.5 per cent of acetic acid has 

 been produced in alcoholic solutions by organisms of this 

 type. 



Vinegar Manufacture. — ^Vinegar may be defined as a 

 solution of acetic acid (usually from 4 to 8 per cent, 

 preferably about 5 to 6 per cent) developed by the fer- 

 mentation of alcoholic solutions of various types. The 

 origin of vinegar is ordinarily indicated by such phrases 

 as "cider vinegar," "wine vinegar," "malt vinegar," 

 "honey vinegar,' etc. The manufacture of vinegar will be 

 discussed under the headings of manufacture in the home 

 and on the farm and commercial manufacture. 



Home Manufacture of Vinegar. — The materials most 

 commonly used for the home manufacture of vinegar are 

 cider or other fruit juices, honey, and artificial sugar solu- 

 tions. The first step in the process is always an alcoholic 

 fermentation, the transformation of the sugar, at least in 

 large part, into alcohol and carbon dioxide. This change 

 may be initiated by the introduction of yeast, but with the 

 fruit juices this usually is not necessary, the native wild 

 yeasts present being sufficiently numerous and active. For 

 the manufacture of a good quality of vinegar it is necessary 

 to have first, a sufficient exposure of surface of the liquid to 

 the air to allow the abundant development of the surface 

 film of acetic bacteria ; second, the rapid transformation of 

 the alcohol into acetic acid due to the presence of desirable 

 acetic bacteria; third, maintenance of the material at a 

 suitable temperature, and finally, some method of stopping 

 the process upon the formation of the maximum amount of 

 acetic acid and before microorganisms have transformed 



