BUTYEIC FERMENTATION 217 



tained because some heat is generated during the process of 

 fermentation, giving rise to convection currents. The bac- 

 teria soon cover the surfaces of the shavings with a con- 

 tinuous film. Conditions are optimum, therefore, for the 

 rapid oxidation of alcohol to acetic acid. After the 

 apparatus is in working order and the shavings thoroughly 

 inoculated and the rate of flow properly adjusted, the 

 alcoholic solution may run in at the top in a continuous 

 stream and vinegar be drawn off at the bottom. 



Butyric Fermentation 



The development of butyric acid (C3H7COOH) in fer- 

 mentation is usually regarded as an undesirable change, 

 although in some operations such as retting of flax and 

 hemp, it may be desirable and even essential. 



Butyric acid is produced in several distinct ways in 

 various fermentative processes. Certain anaerobic bacteria 

 ferment sugars (and in some cases polysaccharides) with 

 the formation of butyric acid and gas, usually carbon 

 dioxide and hydrogen. If the intermediate steps are dis- 

 regarded the reaction may be indicated as follows : 



C.Hj^O, = C3H,C00H + 2C0, + 2H2 



Lactic acid or the lactates may also be fermented by these 

 organisms. The reaction in this case may be represented as : 



2CH3 ■ CHOH • COOH = CgH.COOH + 200^ + 2H, 



In some eases glycerin is fermented with the development 

 of butyric acid. The acid may also originate as a result of 

 the hydrolysis of the fat butyrin. 



Organisms Producing Butyric Fermentation. — Most of 

 the bacteria responsible for butyric fermentation of carbo- 

 hydrates belong to the genus Clostridium; in fact, probably 

 most of the species of this genus produce more or less 



