RELATION OF MICROORGANISMS TO CHEESE. 357 



the characteristic aroma of the cheese in question. The esters it contains 

 are largely those of ethyl alcohol. The acid-forming bacteria, as stated 

 previously, produce varying amounts of volatile acids and slight 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 undergo under the influence of factors yet 

 unknown. The death and disintegration of the lactic bacteria may 

 liberate intracellular enzymes, or possibly, the period of initial bacterial 

 activity is followed by a second in which unknown forms are concerned, 

 the result of whose action is the production of flavoring substances. 



By appropriate means the constant presence of other types of bacteria 

 than the lactic can be demonstrated, but little is known concerning their 

 number and still less of their probable action in cheeses because of the 

 lack of knowledge of the compounds on which they may act or those they 

 may form. That some biological factor is concerned in the production 

 of flavor in Cheddar cheese is indicated by the fact that if changes are 

 made in the methods of manufacture, changes in flavor are likely to result. 

 If the salt is omitted, the typical flavor does not appear. This can be 

 explained only by the action of the salt on certain types of bacteria, which, 

 in its absence, are able to grow and produce compounds that are not 

 found in a normal cheeses. Apparently the methods of manufacture 

 establish a certain equilibrium in the bacterial life which results in the 

 production of definite substances in amounts varying within certain 

 limits. If any condition is varied too widely, a deviation in the microbial 

 balance is produced and the products formed in the cheeses are changed 

 in kind or in amounts, either of which may result in a change of flavor. 



ABNORMAL CHEESES. 



The development of a normal texture and flavor in Cheddar cheese is 

 largely dependent on the presence of definite types of bacteria. If these 

 are replaced, wholly or in part, by other kinds, the product is likely to 

 suffer in texture, flavor or both. As has been emphasized previously, 

 the bacterial content of the milk is of the greatest importance in cheese, 

 since the organisms in the milk pass into the cheese and there produce 



