CHAPTER XXV. 



LACTIC ACID BACTERIA IN DISTILLING, BREWING, 

 AND VINDICATION. 



148. The Spontaneous Acidification of Distillery 

 Yeast-Mash. 



THE preparation of the pitching yeast for distillery work is not 

 such an easy matter as in the sister industry of brewing. In the 

 regular course of the latter no special labour is required for the 

 production of the necessary quantity of yeast, since in this case 

 the yeast settles down, as soon as the fermentation is at an end, to 

 the bottom of the tun, and can then after the immature beer is 

 racked off be used at once for " pitching ' (i.e. inducing fermen- 

 tation in) a fresh quantity of wort. The case is different in 

 distillery work, where the liquid to be fermented, instead of being 

 thin and self-clarifying like wort, is a thick mash, in which the 

 yeast cannot settle down. For this reason the distiller is obliged 

 to prepare his pitching yeast in another way. He grows it arti- 

 ficially in special vats, and, on this account, terms it "artificial 

 yeast." For this purpose a sweet mash is prepared in a small tun, 

 the quantity amounting to about 10 per cent, of the principal 

 mash to be fermented. A more detailed description of the pre- 

 paration of this yeast-mash belongs to the domain of Chemical 

 Technology, and we will here content ourselves with briefly men- 

 tioning that crushed green malt is mixed with water and gradually 

 warmed to 67-7o C., then mixed with a (variable) amount of 

 sweet "goods" from the principal mash tun, and the mixture left 

 to saccharify for two hours at 70 C. Before this medium is 

 pitched with the yeast to be reproduced, it must, however, be sub- 

 jected to another preliminary treatment known as "souring." 



The green malt is infested with a copious flora of various kinds 

 of bacteria, chief among which are the species of the hardy organisms 

 causing butyric fermentation. These spores are not killed by the 

 aforesaid mashing temperature which, moreover, for reasons con- 

 nected with the preservation of the diastase, must not be exceeded 

 and therefore they afterwards germinate and increase, and pro- 

 duce butyric acid. Now this acid, being a powerful yeast poison, 

 would injure the development of the pitching yeast ; but since the 

 injurious bacteria are themselves very sensitive to high degrees of 



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