352 FERMENTATION OF BEER. 



Appert's method of preserving food, and this kind 

 of fermentation of beer, depend on the same prin- 

 ciple. 



In the fermentation of beer after this manner, all 

 the substances capable of decay are separated from 

 it by means of an unrestrained access of air, while 

 the temperature is kept sufficiently low to prevent 

 the alcohol from combining with oxygen. The re- 

 moval of these substances diminishes the tendency 

 of the beer to become acescent, or, in other words, 

 to suffer a further transformation. 



In Appert's mode of preserving food, oxygen is 

 allowed to enter into combination with the substance 

 of the food, at a temperature at which decay, but 

 neither putrefaction nor fermentation, can take place. 

 With the subsequent exclusion of the oxygen and 

 the ?:ompletion of the decay, every cause which could 

 effect further decomposition of the food is removed. 

 The conditions for putrefaction are rendered insuffi- 

 cient in both cases ; in the one by the removal of the 

 substances susceptible of decay, in the other by the 

 exclusion of the oxygen which would effect it. 



It has been stated to be uncertain, whether gluten 

 during its conversion into common yeast, that is, 

 into the insoluble state in which it separates from 

 fermenting liquids, really combines directly with 

 oxygen. If it does combine with oxygen, then the 

 difference between gluten and ferment would be, 

 that the latter would contain a larger proportion of 

 oxygen. Now it is very difficult to ascertain this, 

 and even their analyses cannot decide the question. 

 Let us consider, for example, the relations of alloxan 

 and alloxantin* to one another. Both of these bod- 

 ies contain the same elements as gluten, although in 

 different proportions. Now they are known to be 

 convertible into each other, by oxygen being absorb- 

 ed in the one case, and in the other extracted. Both 



* Products of the decomposition of uric acid by nitric acid, consisting 

 of carbon, nitrogen, hydrogen, and oxygen. See description, &c. in 

 Webster's Chemistry^ pp. 425 and 430. 



