YEAST FROM BEER AND WINE. 311 



CHAPTER IX. 



On Vinous Fermentation : — Wine and Beer. 



It has already been mentioned that fermentation is excited in the 

 juice of grapes by the access of air ; alcohol and carbonic acid 

 being formed by the decomposition of the sugar contained in the 

 fluid. But it was also stated, that the process once commenced, 

 continues until all the sugar is completely decomposed, quite 

 independently of any further influence of the air. 



In addition to the alcohol and carbonic acid formed by the fer- 

 mentation of the juice, there is also produced a yellow or grey 

 insoluble substance, containing a large quantity of nitrogen. It 

 is this body which possesses the power of inducing fermentation 

 in a new solution of sugar, and which has in consequence re- 

 ceived the name of ferment. 



The alcohol and carbonic acid are produced from the elements 

 of the sugar, and the ferment from those azotized constituents of 

 the juice termed gluten or vegetable albumen. 



According to the experiments of De Saussure, fresh impure 

 gluten evolved, in five weeks, twenty-eight times its volume of a 

 gas which consisted of J of carbonic acid, and J of pure hydro- 

 gen gas ; ammoniacal salts of several organic acids were formed 

 at the same time. Water must, therefore, be decomposed during 

 the putrefaction of gluten ; the oxygen of this water must enter 

 into combination with some of its constituents, whilst hydrogen 

 is liberated, a circumstance which happens only in decomposi- 

 tions of the most energetic kind. Neither ferment, nor any 

 substance similar to it, is formed in this case ; and we have seen 

 that hydrogen is not evolved in the fermentation of saccharine 

 vegetable juices. 



It is evident that the decomposition which gluten suffers in an 

 isolated state, and that which it undergoes when dissolved in a 



