432, MICROBIOLOGY OF MILK AND MILK PRODUCTS 



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 compoimds that are not 

 found in a normal cheese. Apparently the methods of manufacture 

 establish a certain equiUbrium 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 micro- 

 bial 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 the same products as they would have done in the uncurdled 

 milk; All abnormalities of the cheese so far as they are occasioned by 

 bacteria are due to the abnormal flora of the milk. To the raw 

 material the maker must direct his attention if a fine product is to be 

 prepared. 



Gassy Cheese.^ — The most frequent trouble encountered and the 

 one of greatest economic importance is the fermentation caused by 

 organisms belonging largely to the B. coli aerogenes group. It has been 

 seen that these produce in milk gases, such as carbon dioxide and 

 hydrogen, and offensive smelling and tasting compoimds. In cheese 

 similar compounds are formed by these organisms; the gas causes the 

 more or less abundant formation of holes which give to the cheese judge 

 an indication of what may be expected with reference to flavor. All 

 milk contains some of the gas-forming organisms, but it is only when 

 they are numerous that marked injury is done. 



Gassy, cheese may also be due to the presence of lactose-fermenting 

 yeasts which are usually found in milk in such small numbers that they 



