THE RELATION OF MICROORGANISMS TO CHEESE 



431 



monia and related compounds. It was thus naturalto consider the flavor 

 due to these simple products of protein degradation. More recently it 

 has been discovered that the intensity of flavor does not necessarily cor- 

 respond to the content of the cheese in these products; indeed a cheese 

 may have a high content of nitrogen as ammonia and yet be low in 

 flavor. 



The Wisconsin Experiment Station has found that the volatile fatty 

 acids of Cheddar cheese increase as the ripening progresses. In the 

 following table are given the data obtained from the detailed study of a 

 normal Cheddar cheese. 



Acids in 100 G. of Dry Matter 



3 days 



Lactic acid. . . 

 Acetic add. . . 

 Propionic acid 

 Butyric acid. . 

 Caproic acid. . 



84.09 



"59 

 0.41 



0.73 

 0.00 



c.c. of N/10 alkali neutralized 



43 days 1 3 months sH months 



90.28 

 29.44 

 .2-15 



2.17 

 0.36 



10 months 



74.10 



12.64 



2.63 



5AS 

 2.23 



It will be noted that the content of the higher volatile acids, those 

 especially marked in odor, continually increases. It is possible to sepa- 

 rate other volatile compounds found in cheese from the volatile fatty 

 acids by distilling with steam, neutralizing the distillate with an alkaU 

 and redistilling; the second distillate will contain the alcohols and esters 

 present in the cheese. Such a distillate prepared from Cheddar cheese 

 is found to possess the characteristic aroma of the cheese in question. 

 The esters it contains are largely those of ethyl alcohol. The acid-form- 

 ing bacteria, as stated previously, produce varying amounts of volatile 

 acids and sUght amounts of alcohols and esters. It is likely that the 

 larger part of the volatile compounds found in the ripening cheese is 

 formed in fermentations which take place subsequent to the initial 

 fermentation of the lactose. The flavor of Cheddar cheese, therefore. 

 Owes its origin very probably to the fermentation of the lactose, and to 

 the further change which the products of the initial fermentation un- 

 dergo imder the influence of biological factors yet unknown. That some 



