35 6 



MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



attacks of putrefactive bacteria; but it is not certain that the cheese will 

 develop a normal flavor when lactic acid is replaced by mineral acids. 



Flavor Production in Cheese. The factors that have been discussed 

 are undoubtedly the most important ones concerned in the proteolysis of 

 the curd, and are thus the factors concerned in the changes of texture, 

 solubility and digestibility. The flavor, which develops during the 

 ripening process, has been regarded as due to the proteolysis of the para- 

 casein. A thoroughly ripened cheese contains a large amount of ammonia 

 and related compounds. It was thus natural to 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 Grams of Dry Matter. 



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

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

 other volatile compounds found in cheese from the volatile fatty acids by dis- 

 tilling with steam, neutralizing the distillate with an alkali 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 



