CHAPTER XV 

 ALCOHOLIC FERMENTATION 



ALCOHOLIC fermentation is the most widely studied 

 of the fermentations, partly because of its wide- 

 spread industrial importance and partly because of 

 the ease with which it can be carried out and the condi- 

 tions modified. About 95 per cent, of the sugar fermented 

 is normally recovered as e qui -molecular proportions of 

 alcohol and carbon dioxide. Gay-Lussac long ago ex- 

 pressed this in the form of the classical equation : — 



CeHiaOe > 2CO2 + 2C2H5OH. 



The fermentation, however, is not so simple as this 

 equation suggests ; in reality the end products arise from 

 a chain of reactions involving a number of intermediate 

 compounds. Besides the alcohol and carbon dioxide there 

 is a constant production of some 3 to 4 per cent, of glycerol, 

 small amounts of fusel oil (derived from the yeast proteins, 

 see Chapter XIII), and varying small proportions of 

 hexose mono- and di -phosphates. 



The first real advance in our laiowledge of alcoholic 

 fermentation was the almost simultaneous proof in 1837 

 by Cagniard-Latour, Schwann and Klitzing that the 

 fermentation was associated with the living organism, 

 yeast. If sugar solutions were sterilised by boiling and 

 only heated air admitted to them no fermentation 

 occurred. 



The next big step forward in the elucidation of the 

 mechanism of alcoholic fermentation occurred when 

 Buchner in 1897 succeeded in demonstrating its enzymatic 

 nature by preparing an active cell -free extract by grinding 



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