MICROBIOLOGY OF FERMENTED FOODS 575 



losses of sugar occurring through fermentation processes. Often 3 

 per cent or more of lactic acid is formed, beet pulp silage in this respect 

 representing one of the most acid types of silage commonly produced. 

 The proteins of the beets also undergo decomposition to a limited ex- 

 tent with consequent reduction of feeding value. Beet cosettes are 

 now dried in most modern mills because of the large losses of feeding 

 value in beet silage and because of the better keeping quality of the 

 dried product. 



Pea vine and other highly nitrogenous materials tend to undergo 

 putrefaction rather than lactic fermentation but make excellent silage 

 when combined with corn or other starchy materials. 



The fermentation of corn silage was first systematically studied 

 by Burrill* who found that the hot fermentations sometimes encount- 

 ered in silage were frequently induced by slow filling of the silo, thus 

 permitting oxidizing thermophilic organisms to develop. Silage near 

 the surface of the filled silo often reaches high temperatures for this 

 same reason. Temperatures of 60 to 70 are not uncommon. 



In the normal fermentations of silage, however, the temperature 

 in the depths of the silo seldom exceeds 35, permitting the growth of a 

 varied microflora in which lactic organisms predominate. Acetic acid 

 and propionic acids have been shown by Dox and Neidig of Iowa to 

 be regular constituents of corn silage. Their results indicate that a 

 small amount of butyric acid is to be found in normal silage and that 

 this often increases in silage of poor quality. Formic acid was found 

 in a few samples. Ethyl alcohol and propyl alcohol occur in deter- 

 minable quantities and higher alcohols in traces. It is believed that the 

 alcohols are formed as a result of bacterial rather than yeast fermenta- 

 tion as the yeasts found in silage are usually of the Mycoderma group 

 rather than of the alcohol-forming types. 



Silage resembles sauerkraut in many respects, although the fact that 

 silage is less watery than sauerkraut modifies the character of the or- 

 ganisms and the intensity of the fermentation. Corn silage normally 

 contains more than i per cent total acid. 



So-called "sweet silage" may be caused in some* cases by thermo- 

 philic fermentation which reaches a high enough temperature to destroy 

 the lactic bacteria or in other cases by the use of material too low in 

 sugar to afford enough of this compound for appreciable lactic acid 



*Burrill, T. J., Biology of Silage. Bulletin 7. Illinois Station, 1889. 



