GLYCEROL FERMENTATION 343 



bacterial filter. This in turn is followed by a treatment of the wine 

 with metabisulphite or sulphur dioxide. 



The reader is referred to The Principles and Practice of Wine 

 Making ^° and Commercial Fruit and Vegetable Products,^^ both by 

 Cruess, for further details. 



The Manufacture of Distilled Alcoholic Products. Whisky, gin, 

 brandy, cordials, and liqueurs constitute the principal distilled spirits. 

 Bourbon whisky may be prepared from corn, malt, and rye. Rye 

 whisky is generally manufactured from rye and barley or rye malt. 

 Scotch whisky is made from barley malt. The fermentation is car- 

 ried out with strains of Saccharomyces cerevisiae. The mash is 

 sometimes also inoculated with lactic acid organisms. After the 

 alcoholic fermentation is complete, the mash is distilled, the type of 

 still and the method of distillation affecting the characteristics of 

 the final product. The raw whisky should be aged in charred new 

 oak containers. 



Gin is obtained by the distillation of the mash with or over juniper 

 berries. Rum is a distilled product manufactured from the fermen- 

 tation of molasses. Brandy is obtained from the distillation of fer- 

 mented juice or the mash of fruit. Cordials and liqueurs are prepared 

 by mixing or redistilling spirits such as neutral spirits (alcohol), 

 brandy, and gin, with or over fruits, flowers and plants. 



Vinegar Manufacture. The manufacture of vinegar essentially 

 involves two steps. The first is the breakdown of sugar in a fruit 

 such as apple, or a malted starchy substance, to alcohol. The sec- 

 ond is the transformation of the alcohol to acetic acid by certain de- 

 sired strains of Acetobacter. The yeast is involved in the first step. 



GLYCEROL FERMENTATION 



An examination of the Embden-Meyerhof-Parnas scheme (see 

 page 326) for the dissimilation of sugar shows that small amounts of 

 glycerol are normally formed by yeasts in their breakdown of glu- 

 cose. It was noted in the discussion of the alcoholic fermentation 

 that phosphorylated triose can serve as the hydrogen acceptor for 

 reduced diphosphopyridine nucleotide, H2-DPN, and be itself re- 

 duced to glycerophosphate. The phosphoric acid is split off and 

 glycerol is formed. In the normal alcoholic fermentation this does 

 not occur because acetaldehyde acts as the hydrogen acceptor for 

 H2-DPN and is reduced to ethyl alcohol. Accordingly, only small 

 quantities of glycerol are generally produced. 



