CHEESE 625 



If Bacillus coli or B. aerogenes is present enough gas is formed 

 to cut small holes in the curd. The B. subtilis group may also 

 produce a smooth coagulum, but this is redissolved later. 



3. The curd may be granular, with whey enclosed and fissures. 

 This shows the presence of Bacillus coli, Streptococcus lacticus, 

 and liquefying cocci. 



4. The curd adheres to the walls of the vessel arid the whey is 

 greenish white and has a sharp, sour taste. The Bacillus coli 

 group and micrococci are well represented. 



5. The curd is heavily charged with gas-bubbles and rises to 

 the surface (floater or floating curd). Large numbers of the 

 Bacillus coli group are present. 



Of course these are only types, many variations being possible. 



The catalase test (page 237) is of use to the cheese maker in 

 discovering abnormal conditions in milk. This test shows the 

 presence of colostrum milk, old milk, milk derived from cows 

 near the end of lactation, or milk from diseased cows. Milk 

 from cows suffering from udder disease or gastro-intestinal dis- 

 turbances gives a positive catalase test. 



In some cheese factories a small amount of potassium nitrate 

 is added to the milk to prevent gassy fermentation. The amount 

 necessary is from 0.04 to 0. 1 per cent. Potassium nitrate protects 

 the milk-sugar against attack by Bacillus coli or B. aerogenes, as 

 they derive their oxygen supply from the nitrate instead of the 

 milk-sugar. 



A not uncommon trouble with cheese is the appearance of 

 small yellowish-red spots or patches, the so-called "rusty spot." 

 As a matter of fact, these spots are more common than is generally 

 supposed, but frequently the color of the spots is so light that 

 they are covered by the coloring-matter often added to the cheese. 

 The "rusty spots" are colonies of bacteria, variously named Bac- 

 terium casei fusci. Micrococcus chromoflavus, and Bacillus 

 rudensis. B. rudensis is probably more frequently the cause of 

 rusty spots than the others. 



Yellow color and white spots in Cheddar cheese are due to the 

 action of Bacillus coli and torulse. 



Bitter cheese is caused by several bacteria and torulse. Freud- 



enreich's Micrococcus casei amari and Harrison's torula amara 



have been isolated from bitter cheese. Harding, Rogers, and 



""^Sinith found a short bacillus as the cause of a bitter taste in Neuf- 



chatel cheese. 



The same authors ascribe the sweet or fruity flavor, which 

 causes an annual loss of at least $10,000 worth of Cheddar cheese, 

 to the presence of yeasts, although yeasts are rarely found in 

 normal Cheddar cheese. 



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