THE BAVARIAN PROCESS. 321 



The ordinary frothy yeast may be removed from fermenting 

 beer by filtration, without the fermentation being thereby arrest- 

 ed ; but the precipitated yeast of Bavarian beer cannot be 

 removed without the whole process of its fermentation being in- 

 terrupted. 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 temperature of 

 between 40° and 50° F., a slow tranquil fermentation 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 operation 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 temperature, with 

 this kind of yeast, the condition necessary for the transformation 

 of the sugar is the presence of that yeast ; but for the conversion 

 of gluten into ferment by a process of oxidation, something more 

 is required. 



When the power of gluten to attract oxygen is increased by 

 contact with precipitated yeast in a state of decay, the unre- 

 strained access of air is the only other condition necessary for its 

 own conversion into the same state of decay, that is, for its oxida- 

 tion. We have already seen that the presence of free oxygen 

 and of gluten are conditions which determine the eremacausis of 

 alcohol and its conversion into acetic acid, but they are inca- 

 pable of exerting this influence at low temperatures. A low 

 temperature retards the slow combustion of alcohol, while the 

 gluten combines spontaneously with the oxygen of the air, just 

 as sulphurous acid does when dissolved in water. Alcohol un- 

 dergoes no such change at low temperatures, but during the oxi- 

 dation of the gluten in contact with it, is placed in the same 

 condition as the gluten itself when sulphurous acid is added to 

 15* 



