466 IOWA DEPARTMENT OF AGRICULTURE 



and the evolution of carbonic acid gas.* The temperature of the silage 

 rarely exceeds 85° to 90° Fahrenheit, except near the surface, where fer- 

 mentative processes are greater, owing to the presence of air. Erroneous 

 ideas regarding the importance of the heating in silage fermentation 

 were derived from observations made only on the surface of the silage. 

 The oxygen in the silage is used up early in the process of fermentation 

 or driven out by the carbonic acid gas. Fro7n this point the presence 

 of air or oxygen is fatal to the proper preservation of the silage, because 

 air permits the development of molds, which are themselves sometimes 

 poisonous, and which quickly destroy the acids and thus allow the silage 

 to spoil. The importance of air-tight walls and proper packing down of 

 the silage to keep out the air is, therefore, at once apparent. 



THE FOR'MATION OF ACIDS. 



The next changes noticed during the silage-making process are a 

 change in color, and the development of a more or less pleasant aromatic 

 odor and a sour taste. The color and odor are characteristics of silage 

 and are of considerable value in judging its quality; but the most im- 

 portant change is the formation of acids, which cause the sour taste. 

 The acids formed are chiefly lactic acid, which is the acid found in 

 sour milk, and acetic acid, the acid of vinegar. The total amount of 

 acid formed averages between 1 per cent and 2 per cent of the weight 

 of the silage. This change is important because it indicates that the 

 fermentation is healthful, like the ripening of cream or the formation 

 of vinegar, instead of being a state of unhealthful decay, like the putre- 

 faction or spoiling of meat. In the presence of this acid fermentation 

 it is impossible for the bacteria which cause decay to live and work, 

 unless the presence of air should allow the growth of molds, which in 

 turn destroy the acids, and thus allow the putrefactive bacteria to thrive. 

 This last process is what occurs in the top layer of the silage in the 

 silo, which is spoiled because of the presence of air. The formation 

 of acid is, therefore, one of the most important of the changes which 

 take place in the fermentation of silage. 



THE' FORMATION OF ALCOHOLS. 



Other changes occur in the process which are not appreciable to the 

 senses, and which can generally be detected only by chemical analysis. 

 One of these is the formation of a small amount of alcohols, chiefly 

 ordinary or grain alcohol. The total amount of alcohols generally varies 

 between 0.1 per cent and 0.4 per cent of the weight of the silage, or 

 as much as 0.5 per cent of the juice. The source of the alcohols, as 

 well as of the acids, is the sugar originally present in the plant. Experi- 

 ments conducted by the writer show that the amount of sugar which 

 disappears is almost exactly equivalent to the amount of alcohol and 



*Thls gas is generally known to be poisonous, but accidents still occur 

 occasionally when the gas, which is heavier than air, collects in a partially 

 filled silo. If a lighted lantern is lowered into the silo is extinguished, it 

 is almost certain death to enter before the gas has been driven out by 

 starting the silo-filler or by opening a door near the surface of the silage. 



