CHAPTER IV 

 THE MANUFACTURE OF VINEGAR 



ACETIC FERMENTATION 



NATURE AND ORIGIN OF VINEGAR. Vinegar is a condiment made 

 from various sugary or starchy matters by alcoholic and subsequent 

 acetic fermentation. It should contain from 4 to 8 per cent of acetic 

 acid and natural flavoring, coloring and other matters, varying accord- 

 ing to its origin. 



Acetic acid (CH 3 COOH) is a monobasic organic acid, the second in 

 the fatty acid series. It is a colorless liquid with a strong suffocating 

 odor, crystalizing when pure at 16.7 and at lower temperatures when 

 diluted with from i to 13 per cent of water. Its specific gravity is 1.08 

 at o and it boils at 118 under 760 mm. pressure, producing an inflam- 

 mable vapor. It is a solvent of many organic substances and is soluble 

 in water and alcohol in all proportions. 



The metallic acetates are poisonous and are formed in most cases 

 by simple contact of metal and acid. Certain alloys of tin resist the 

 action of the acid. 



Acetic acid is formed by the oxidation of ethyl alcohol which takes 

 place in two stages according to the following reactions: 



2C 2 H 5 OH -f- 0<T = 2CH 3 CHO + 2H 2 O 



Ethyl + Oxygen = Acetic + Water, 

 alcohol aldehyde 



2CH 3 CHO + O 2 = 2 CH 3 COOH 



Acetic + Oxygen = Acetic acid, 

 aldehyde 



These reactions may be brought about by chemical means, but in 

 practice they are due to the action of certain microorganisms, mainly 

 bacteria. Acetic acid is also made by the distillation of wood but the 

 product is not suitable for consumption. 



VINEGAR BACTERIA. If wine, beer or a similar organic solution con- 

 taining alcohol, is exposed freely to the air it soon becomes covered 

 with a film, the alcohol disappears, is replaced by acetic acid and the 

 liquid is converted into vinegar. 



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