298 FERMENTATION OF BEER. 



the gluten dissolved in the wort ; oxygen gas is 

 absorbed from the air, and all the gluten in solution 

 is deposited as yeast. 



The ordinary frothy yeast may be removed from 

 fermenting beer by filtration, without the fermen- 

 tation being thereby arrested; but precipitated 

 yeast of Bavarian beer cannot be removed without 

 the whole process of its fermentation being inter- 

 rupted. The beer ceases to ferment altogether, or, 

 if the temperature is raised, undergoes the ordinary 

 fermentation. 



The precipitated yeast does not excite ordinary 

 fermentation, and consequently is quite unfitted for 

 the purpose of baking, but the common frothy 

 yeast can cause the kind of fermentation by which 

 the former kind of yeast is produced. 



When common yeast is added to wort at a tempera- 

 ture of between 40 and 45 F., a slow tranquil fer- 

 mentation takes place, and a matter is deposited on 

 the bottom of the vessel, which may be employed to 

 excite new fermentation ; and when the same oper- 

 ation is repeated several times in succession, the 

 ordinary fermentation changes into that process by 

 which only precipitated yeast is formed. The yeast 

 now deposited has lost the property of exciting 

 ordinary fermentation, but it produces the other 

 process even at a temperature of 50 F. 



In wort subjected to fermentation, at a low tem- 

 perature, with this kind of yeast, the condition 



