296 FERMENTATION OF BEER. 



in which the vessels are placed,, is never allowed to 

 rise above from 45 to 50 F. The fermentation 

 lasts from three to six weeks, and the carbonic acid 

 evolved during its continuance is not in large 

 bubbles which burst upon the surface of the liquid, 

 but in small bubbles like those which escape from a 

 liquid saturated by high pressure. The surface of 

 the wort is scarcely covered with a scum, and all 

 the yeast is deposited on the bottom of the vessel 

 in the form of a viscous sediment. 



In order to obtain a clear conception of the great 

 difference between the two kinds of fermentation, 

 it may perhaps be sufficient to recall to mind the 

 fact, that the transformation of gluten or other azo- 

 tised matters is a process consisting of several stages. 

 The first stage is the conversion of the gluten 

 into insoluble ferment in the interior of the liquid, 

 and as the transformation of the sugar goes on at 

 the same time, carbonic acid and yeast are simulta- 

 neously disengaged. It is known with certainty, 

 that this formation of yeast depends upon oxygen 

 being appropriated by the gluten in the act of 

 decomposition ; but it has "not been sufficiently 

 shown, whether this oxygen is derived from the 

 water, sugar, or from the gluten itself ; whether it 

 combines directly with the gluten, or merely with 

 its hydrogen, so as to form water. For the purpose 

 of obtaining a definite idea of the process, we may 

 designate the first change as the stage of oxidation. 



