THE PKODUCTION OF ALCOHOL 



217 



Next, yeast is added and allowed to grow and multiply for about 

 14-16 hours. This gives the distiller a slightly acid liquid, devoid of 

 injurious organisms and containing a healthy culture of yeast. This 

 preparation is added to the mash-tun containing the bulk of the 

 " sweet goods," when brisk fermentation takes place ; the yeast rapidly 

 multiplies, and in doing so uses up the sugar and forms alcohol. 



When fermentation is completed, the product is distilled several 

 times, the distillates becoming progressively stronger in alcohol because 

 this substance vaporises at a lower temperature than the other con- 

 stituents contained in the fermented mass. 



The flavour of whiskey does not depend on the alcohol, but rather 

 on small quantities of other volatile substances that come over with the 

 alcohol in the distillation. The flavour of some brands of Scotch 

 whiskey is due to the use of peat fires in the preparation of malt. 



(c) Wine. Wine is prepared by the fermentation of grape juice. 

 The expressed juice of the grape is known as must, and contains from 

 15 to 33 per cent, of the sugar glucose. The old-fashioned method of 

 preparing wine consisted in leaving the fermentation to chance. Must 

 usually contains one or more individuals belonging to one of the 

 yeasts, and when left alone multiplication 

 takes place, a portion of the glucose being 

 used up and alcohol produced. In many 

 places this method is still employed, and 

 there can be no doubt that in wine-grow- 

 ing districts the chances are greatly in 

 favour of the right fermentation being 

 developed, because in such places yeasts 

 are present in the soil in large numbers, 

 and also because must is a better nutritive 

 medium for yeasts than for other micro- 

 organisms. At the same time there will 

 always be an element of danger, and the 

 modern method of using pure cultures 

 reduces the risks of a wrong fermenta- 

 tion to a minimum. Thus a yeast known 

 as Saccharomyces ellipsoideus I. was found by Hansen on the surface 

 of ripe grapes in the Vosges district. There can be little doubt that 

 this species is mainly responsible for the wine-fermentation of this* 

 neighbourhood. Its general appearance is seen in Fig. 122, the dis- 

 tinguishing feature being the shape of the cells, some being ellipsoidal, 

 others being more sausage shaped. As this species was isolated and 



FIG. 122. Sacchai-omyces ellip- 

 soideus I. (Hansen.) 



