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CHAPTER V. 



The Alcoholic Ferments. 



§ I. — On the Origin of Ferment. 



Amongst the productions that appear spontaneously, or, we 

 should rather say, without direct impregnation, in organic 

 liquids exposed to contact with the air, there is one that more 

 particularly claims our study. It is that one which, by reason 

 of its active energy as an agent of decomposition, has been dis- 

 tinguished and utilized from the earliest times, and is considered 

 as the type of ferments in general ; we mean the ferment of 

 wine, beer, and more generally, of all fermented beverages. 



Yeast is that viscous sort of deposit which takes place in the 

 vats or barrels of must or wort that is undergoing fermentation. 

 This kind of ferment presents for consideration a ph3^sical fact 

 of the most extraordinary character. Take a morsel of the 

 substance and put it in sweetened water, in must, or in dough, 

 which always contains a little sugar ; after a time, the length 

 of which varies, a few minutes often sufficing, we see these 

 liquids or the dough rise, so to speak. This inflation of the 

 mass, which is due to a liberation of carbonic acid gas, 

 may cause it to overflow the vessels containing it, if their 

 capacity is not considerably greater than the volume of the 

 matters fermenting. It is equally remarkable that these pheno- 

 mena are natural and spontaneous ; that is to say that the must, 

 the wort, and the dough are able to rise, as we have termed it, 

 when left to themselves, without the least addition of foreign 



