294 FERMENTATION OF BEER. 



matter is effected without the alcohol undergoing 

 the same change, a higher temperature being 

 necessary to enable alcohol to combine with oxygen. 

 As long as the wine in the stilling-casks deposits 

 yeast, it can still be caused to ferment by the addi- 

 tion of sugar, but old well-layed wine has lost this 

 property, because the condition necessary for fer- 

 mentation, namely, a substance in the act of decom- 

 position or putrefaction, is no longer present in it. 



In hotels and other places .where the wine is 

 drawn gradually from, a cask, and a proportional 

 quantity of air necessarily introduced, its erema- 

 causis, that is, its conversion into acetic acid, is 

 prevented by the addition of a small quantity of sul- 

 phurous acid. This acid, by uniting itself with the 

 oxgyen of the air contained in the cask, or dis- 

 solved in the wine, prevents the oxidation of the 

 organic matter. 



The various kinds of beer differ from one another 

 in the same way as the wines. 



English, French, and most of the German beers, 

 are converted into vinegar when exposed to the 

 action of air. But this property is not possessed 

 by Bavarian beer, which may be kept in vessels only 

 half-filled without acidifying or experiencing any 

 change. This valuable quality is obtained for it 

 by a peculiar management of the fermentation of 

 the wort. The perfection of experimental know- 

 ledge has here led to the solution of one of the 



