322 FERMENTATION OF BEER. 



the wine in which it is contained. The oxygen of the air 

 unites both with the gluten and alcohol of wine not treated with 

 sulphurous acid ; but when this acid is present it combines with 

 neither of them, being altogether absorbed by the acid. The 

 same thing happens in the peculiar process of fermentation 

 adopted in Bavaria. The oxygen of the air unites only with 

 the gluten and not with the alcohol, although it would have 

 combined with both at higher temperatures, so as to form 

 acetic acid. 



Thus, then, this remarkable process of fermentation with the 

 precipitation of a mucous-like ferment consists of a simultaneous 

 putrefaction and decay of the same liquid. The sugar is in the 

 state of putrefaction, and the gluten in that of decay. 



Apperr's method of preserving food, and this kind of fermenta- 

 tion of beer, depend on the same principle. 



In the fermentation of beer after this manner, all the sub- 

 stances capable of decay are separated from it by means of an 

 unrestrained access of air, while the temperature is kept suffi- 

 ciently low to prevent the alcohol from combining with oxygen. 

 The removal 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 tem- 

 perature at which decay, but neither putrefaction nor fermenta- 

 tion, can take place. With the subsequent exclusion of the 

 oxygen and the completion of the decay, every cause which 

 could effect further decomposition of the food is removed. The 

 conditions for putrefaction are rendered insufficient 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 v: 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 



