86 HARVESTING AND UTILIZING CORN 



near the surface, where fermentative processes are greater, owing 

 to the presence of air. Erroneous ideas regarding the importance 

 of the heating in silage fermentation were derived from observa- 

 tions 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. From this point tlie presence of air or 

 oxygen is fatal to tli& 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 pack- 

 ing down of the silage to keep out the air is, therefore, at once 

 apparent. 



" THE FORMATION 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 character- 

 istic of silage and are of considerable value in judging its quality; 

 but the most important 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 ripen- 

 ing of cream or the formation of vinegar, instead of being a state 

 of unhealthful decay, like the putrefaction 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. 



" 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 alco- 

 hols, chiefly ordinary or grain alcohol. The total amount of alco- 

 hols generally varies between 0.1 per cent and 0.4 per cent of the 



