THE RELATION OF MICROORGANISMS TO CHEESE 433 



cannot compete with the lactic bacteria in the fermentation of the sugar 

 in the cheese. At times the number may be increased to such an extent 

 that the major part of the sugar is fermented by them, alcohol and car- 

 bon dioxide being produced. An outbreak of gassy Swiss cheese was 

 found by Russell and Hastings to be due to such yeasts that had gained 

 entrance to the milk from the whey-barrels because of careless washing 

 of the milk cans. The cheese makers of the country are realizing the 

 importance of the contamination of the milk from the transportation of 

 whey and milk in the same can. The most practical means of prevent- 

 ing trouble from this practice is to heat the whey to 68° as it passes from 

 the cheese vat to the storage tank. This temperature destroys the 

 harmful microorganisms, and if the storage tank is kept in a sanitary 

 condition the whey is sweet when returned to the farm in the milk can. 

 It has been demonstrated that such a treatment of the whey results in a 

 marked improvement in the quality of the product. 



Miscellaneous Abnormalities of Cheese. — Bitter cheese is 

 produced by bacteria that form a bitter principle. An outbreak of 

 bitter cheese investigated by Hastings was found to be due to the re- 

 placement of the normal acid-forming flora by a lactic organism which 

 produced such an intense bitterness as to mask the acid taste in the 

 milk and cheese. 



Colored cheese is produced by chromogenic bacteria. In case the 

 colonies are not numerous and the pigment formed is not soluble in any 

 of the constituents of the cheese, the color will appear as colored specks, 

 such as the rusty spot investigated by Connel and Harding, which is due 

 to red forms of B. rudensis. If the colonies are very numerous, or if 

 the pigment is soluble, the curd may be uniformly colored. 



Putrid cheese is caused by the absence of sufficient acidity to hold 

 the putrefactive bacteria in check. This trouble is rare in cheddar 

 cheese, since such cheese is made from ripened milk. Fruity flavors are 

 asserted to be due to yeasts which form fruit esters. 



Moldy Cheese. — In the moist air of the curing-room the cheese forms 

 an excellent substratum for the growth of common molds whose pig- 

 mented spores discolor the surface of the cheese and thus impair its 

 value because of the appearance rather than by any effect in the flavor. 

 Cheddar cheese is protected effectively from molds by dipping the 

 cheese, when two or three days old, in melted paraffin which excludes 

 the air from the spores on the surface of the cheese. 



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