240 CHYMISTRY APPLIED TO AGRICULTURE. 



• 



Those fruits from which the juice is expressed to undergo 

 the vinous fermentation, contain both these principles, but 

 they exist in them separately : the extraction of the juice by 

 pressure, mixes them intimately, and they then act upon and 

 decompose each other. 



In well-ripened grapes, the two principles exist in the 

 exact proportions for producing the best results from fer- 

 mentation ; but in the grains which are equally used for the 

 fabrication of spirituous liquors, the sugar is separated when 

 the grain is made to germinate, before being submitted to 

 fermentation.* 



Some of the substances which by fermentation yield al- 

 cohol, require the addition of some foreign matter, in order 

 that fermentation may commence and pass regularly through 

 its various stages. The substance used for exciting fer- 

 mentation, is called leaven, ferment, or yeast; and is al- 

 most always a partially fermented matter containing a large 

 portion of the vegeto-animal principle. The scum which 

 rises upon the top of liquids undergoing fermentation, or a 

 fermented dough of wheat, rye, or barley, is used for this 

 purpose. 



Leaven, when mixed with any liquid containing sugar, 

 continues to ferment, and communicates the action through 

 the whole extent of it. 



When the must of grapes has, by boiling and evapora- 

 tion, been reduced to the state of an extract, the vegeto- 

 animal principle contained in it is disorganized, and it can- 

 not be made to ferment without the addition of some foreign 

 body. 



In order that fermentation may pass regularly through 

 its several stages, and furnish a product free from all ten- 

 dency to a spontaneous and final decomposition, it is ne- 

 cessary that the sugar and leaven should exist in the sub- 

 stance in suitable proportions : — if the proportion of sugar 

 be too great, it will not be entirely decomposed, and the 

 fermented liquor will retain a sweet taste : if, on the other 

 hand, the quantity of leaven predominate, a part of it will 

 remain undecomposed in the mass, and the nature of it 



* In the process of germination, oxygen, which is the sole agent, 

 combines with the carbon, and causes the developement of sugar in 

 the grain. However, the fermentation of grain which has not first 

 germinated, produces gradually the same results when distilled ; as 

 the first effect of fermentation as well as of germination is to throw 

 off carbon. 



