TYPES OF FERMENTATION AND DECAY 27 
TYPES OF FERMENTATION AND DECAY 
The various processes known as fermentation, decay, putre- 
faction, etc., are all closely related, and, while an attempt has 
been made to distinguish between them, no real logical distinc- 
tions can be made. They are all progressive chemical changes 
taking place under the influence of organic substances which are 
present in small quantity in the fermenting mass. ‘They are funda- 
mentally of the nature of chemical decompositions by means of 
which organic substances are broken down and new substances 
are formed. ‘They may best be understood by the consideration 
of three examples illustrating three different types: 
Alcoholic Fermentation——-When yeast is added to a sugar 
solution, it grows rapidly and soon changes the sugar into carbon 
dioxide and alcohol. The sugar is probably taken into the body 
of the yeast and decomposed into these two products, which are 
then liberated from the yeast, the gas appearing as bubbles and 
the alcohol remaining in the solution. The change is sometimes 
expressed by the chemical equation, CsH»:Os = 2C2H.eO + 
2CO,. But this equation represents only the end-products and 
by no means correctly expresses the changes that occur. This 
fermentation occurs in malt to make beer, in apple juice to make 
cider, and is the basis of alcoholic industries in general. It also 
occurs in the raising of bread. 
The Amyolytic Fermentation.—If a litile saliva is mixed 
with starch and water, there begins at once a conversion of the 
starch into sugar, and it may continue until all the starch is thus 
changed. This fermentation is also expressed by a chemical 
equation, CsHi00s + H2O = CsHi20¢, though the equation cer- 
tainly does not represent the change that goes on. Starch is 
known not to be such a simple molecule as CgHi905, but some 
multiple of that formula, and probably a very high one. Its 
decomposition into sugar is really a long series of steps, only the 
final result being partly represented in the equation. This fer- 
