FERMENTS AND ARTIFICIAL FERMENTATIONS. 81 



order to establish fermentation. The yeast is procured 

 by collecting the scum of fermented beer and straining 

 it into bags. 



In Belgium, the wort is allowed to stand until the 

 spontaneous development of fermentation takes place ; 

 but in France and Germany the ferment is generally 

 added. In this case two methods are in use, fermenta- 

 tion from above, and fermentation from below ; and this 

 enables us to distinguish two kinds 

 of yeast, that of superior, and that of 

 inferior beer (Figs. 45, 47). 



In superior beer, the saccharifica- 

 tion of the starch of malt is effected 

 by successive steepings in casks at 

 the relatively high temperature of 

 from 15 to 18. As the yeast is 

 formed, it gradually issues from the 

 bung-holes in the upper part of the 

 cask; hence its name. In England, large open vats 

 are used : the yeast rises to the top, and is removed 

 with skimmers. 



In the manufacture of inferior beer, saccharifica- 

 tion is effected by steeping the malt in open vats at 

 the lower temperature of from 12 to 14. The 

 yeast is deposited at the bottom of the vats in a 

 doughy and tenacious mass. When the first and 

 most active fermentation is at an end, the clear liquid 

 is drawn off and put into casks, bottles, or pitchers, 

 and as the separation of the yeast is not yet complete, 

 6 



Fig. 47. Yeast of in- 

 ferior beer in process 

 of budding (x 400 

 diain.> 



