Il8 BACTERIA 



C 6 Hj 2 O 6 (plus the yeast) = 2 C 2 H 6 O + 2 CO 2 . 



A natural sugar, like grape-sugar, present in the fruit of 

 the vine, is thus fermented. The alcohol remains in the 

 liquid ; the carbonic acid escapes as bubbles of gas into the 

 surrounding air. It is thus that brandy and wines are made. 

 If we go a step further back, to cane-sugar (which possesses 

 the same elements as grape-sugar, but in different propor- 

 tions), dissolve it in water, and mix it with yeast, we get 

 exactly the same result, except that the first stage of the 

 fermentation would be the changing of the cane-sugar into 

 grape-sugar, which is accomplished by a soluble ferment 

 secreted by the yeast cells themselves. If now we go yet 

 one step further back, to starch, the same sort of action 

 occurs. When starch is boiled with a dilute acid it is 

 changed into a gum-like substance named dextrin, and sub- 

 sequently into a sugar named maltose, which latter, when 

 mixed with these living yeast cells, is fermented, and results 

 in the evolution of carbonic acid gas and the production of 

 alcohol. In the manufacture of fermented drinks from 

 cereal grains containing starch there is therefore a double 

 chemical process : first the change of starch into sugar by 

 means of conversion? and secondly the change of the sugar 

 into alcohol and carbonic acid gas by the process of fer- 

 mentation, an organic change brought about by the living 

 yeast cells. 



In all these three forms of alcoholic fermentation the 

 principal features are the same, viz., the sugar disappears; 

 the carbonic acid gas escapes into the air; the alcohol re- 

 mains behind. Though it is true that the sugar disappears, 

 it would be truer still to say that it reappears as alcohol. 

 Sugar and alcohol are built up of precisely the same ele- 

 ments: carbon, hydrogen, and oxygen. They differ from 



1 A chemical change obtained by the action of sulphuric or some other acid, 

 or by the influence of diastase. 



