GRAPE SUGAR AIOJ^E FERMEIfTS. 113 



rvhat onier they shall take place ? How much depends upon the re- 

 fined and little understood mechanism of the vegetable structure — how 

 much on the living principle itself! What is this living principle — 

 how can it direct !* 



§ 7. Of the fermentation of starch and sugar — and of the relative circum- 

 stances under ivhich cane and grape sugars generally occur in nature. 

 It will be of use to us, in connection with the above transformations, 

 to advert to the property possessed by starch and nearly all the known 

 varielies of sugar of entering into fermentation under favourable cir- 

 cumstances. When flour is made into a paste with leaven or yeast it 

 begins to rise and ferment, — sooner or later, according to the kind of 

 flour and the quantity of ferment added. When to a decoction of malt 

 or to a solution of starch or of cane or grape sugar in water, a portion of 

 yeast is added, fermentation is speedily induced ; and if not arrested by 

 unfavourable circumstances it will continue until the whole of the 

 starch or sugar disappears. 



In all these cases it is grape sugar alone that undergoes fermentation. 

 [Rose, Poggen. Annal., lii., p. 297.] The starch of the moist dough or 

 of the solution is partially transformed into grape sugar before fermenta- 

 tion commences. Such is the case also with the decoction of malt and 

 with cane sugar. The fermentation commences soon after the first por- 

 tion of grape sugar is formed, and proceeds more or less rapidly accord- 

 ing as this transformation is more or less speedily effected. Hence, in* 

 the art of brewing, the necessity of cautiously regulating the tempera- 

 ture by which this change of the starch and sugar is promoted and hast- 

 ened. 



The fermentation itself is the result not of a mere transformation of 

 one form of matter into another having the same elementary constitu- 

 tion, but of a decomposition of one substance into two others unlike itself 

 either in properties or in chemical composition. The grape sugar is re- 

 solved into alcohol (spirits of wine), which remains in the liquid, and info 

 carbonic acid, which escapes in the form of gas and causes the fermen- 

 tation. Thus alcohol being represented by C4 Hg O2, and carbonic acid 

 by CO,, 



2 of alcohol r= Cg H,2 O4 and 



4 of carbonic acid = C4 O3 make up 



1 of grape sugar =C),2H,20,2. 



It is an interesting fact that the cane and grape sugars occur in na- 

 ture in circumstances which are entirely consistent with the statement 

 in the preceding section, regarding the action of acids on the former 

 variety of this natural product. Fruits contain grape sugar, which in- 

 creases in quantity as they ripen or become less sour. In the sugar 

 cane, the beet root, and the maple and birch trees, cane sugar exists, 

 but in their juices no acid is associated with the sugar. On the contra- 

 ry, ammonia is known to be present in most of them along with the 

 cane sugar. Hence it is inferred, that as in our hands and in our exper- 

 iments cane sugar is changed by the agency of acids into grape sugar, and 



• »* Oanst thou by searching find out God— Canst thou find out the AJmighty unto perfection 1" 



