CHAPTER V. 



FERMENTATION. 



Fermentation is a peculiar decomposition or transformation of the ele- 

 ments of a complex organic substance, by the agency of some 

 external disturbing force different from ordinary chemical attraction, 

 as heat, air, or contact with some other body similarly affected. 



Liebig. 



THE compounds which are capable of fermentation, or any 

 similar change, are those in which a weak affinity or equilib- 

 rium exists, and is consequently easily disturbed and overcome, 

 by several different agencies, such as heat, acids, oxygen, 

 chlorine, &c. If we add to a solution of sugar and water a 

 small quantity of any organic substance which is itself in the 

 act of slow decomposition, the sugar becomes affected in the 

 same way, and is changed to carbonic acid and alcohol 



This is called vinous fermentation: another form of vinous 

 fermentation is that which takes place in the transformation of 

 must into wine: when the expressed juice of the grape is 

 exposed to a temperature of about 70 F., its own temperature 

 is raised, carbonic acid is given off, a scum rises to the surface* 

 and a sediment subsides to the bottom, and the must is changed 

 to wine. This is the simplest case of fermentation : yeast is 

 peculiarly effective in producing this kind of fermation. Yeast 

 is the product of the vegetable gluten or albumen in fermen- 



