INDUSTRIAL FERMENTATIONS 311 



In America glycerol was produced by maintaining the 

 medium alkaline with sodium bicarbonate, conditions 

 under which acetaldehyde tends to undergo dismutation 

 with formation of acetic acid and alcohol. Glycerol is 

 formed in amounts corresponding to the quantity of 

 acetaldehyde diverted from its normal function of acting 

 as hydrogen acceptor in the formation of pyruvic acid 

 (see p. 277). 



The British method gives the best yields, but the 

 recovery of glycerol is difficult owing to the interference 

 of the sulphite. Moreover, there is little or no market 

 for the acetaldehyde produced as a by-product. The 

 American method, although giving lower yields, is the 

 best commercially, since alcohol is also formed and the 

 proportion of glycerol and alcohol produced can be easily 

 varied according to demand by adjustment of the degree 

 of alkalinity. 



Molasses or hydrolysed wood pulp or similar vegetable 

 w^astes serve as an effective sugar source for the growth of 

 the yeast in glycerol fermentation. 



Power Alcohol Production. — The production of alcohol 

 for fuel purposes and for use in the chemical and other 

 industries has grown very largely within the past ten to 

 fifteen years. The fermentation is generally carried out 

 by the use of an appropriate strain of yeast to ferment 

 molasses, which provides an excellent source of carbo- 

 hydrate, nitrogen and mineral salts in immediately avail- 

 able condition. An inoculum is built up from a pure 

 culture of the yeast, maintained in the laboratory, by 

 successive transfers to increasing quantities of molasses 

 until a " seed " is obtained, about 5 per cent, of the final 

 volume to be fermented. The molasses is maintained at 

 pH 5, which allows good gro\vth of the yeast but inhibits 

 the gro\\i:h of most bacteria which might act as 

 contaminants. After fermentation for about forty-eight 

 hours the alcohol, present to the extent of 5 to 10 per 

 cent., is distilled off from the mash. 



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