CHAPTER XVII 



ACETIC, BUTYEIC, OXALIC AND CITEIC FERMENTATION— 

 THE GENERA ACETOBACTEE, BACTERIUM, CLOSTEID- 

 lUM, ASPEEGILLU8 AND CITEOMYCES. 



Many different acids have been described as produced by 

 microorganisms. Among the most important in this list are 

 formic, acetic, propionic, butyric, valerianic, succinic, lactic, 

 oxalic, and citric. Of these, lactic acid has already been 

 discussed. Acetic, butyric, oxalic and citric acids are of 

 considerable economic importance. 



Acetic Fermentation 



Many microorganisms are known which are capable of 

 producing acetic acid. Comparatively few of these, how- 

 ever, are of economic significance. Acetic acid production 

 is most important in the manufacture of vinegar for use as 

 a condiment, although large quantities are produced by 

 bacterial fermentation for the manufacture of ingredients 

 (particularly amyl acetate) used in making certain ex- 

 plosives. Small quantities of acetic acid are also produced 

 in many fermented foods such as sauerkraut, ensilage, and 

 fermented pickles. 



Types of Acetic Acid Fermentation. — Bacteria produc- 

 ing acetic acid may be divided into two groups; those 

 which bring about the change under aerobic conditions, 

 oxidizing alcohol to acetic acid; and those which bring 

 about fermentation of sugars under anaerobic conditions, 

 acetic acid being one of several of the products. 



Alcoholic solutions, such as wine, beer or cider, when 

 allowed to stand open to the air soon become covered with a 

 growth popularly termed mother of vinegar. This is com- 



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