DEFECTS IN BUTTER 227 



2. DEFECTS IN BUTTER. 



Whilst butter-making by any one of these three methods will very 

 seldom be attended by serious mishaps, the close dependence of ripening 

 on the fermentation of bacteria and the ever-changing nature of the 

 bacterial contents in any prescribed space render butter-making a risky 

 process to those who do not take any special precautions. It may and 

 does sometimes happen that ripening does not proceed normally, 

 unpleasant smells being given off, and the flavour being offensive. 

 During the time that elapses between the milking and the churning, 

 the cream is exposed on all sides to the attacks of many species of 

 bacteria, and the vicinity of the byre is peculiarly rich in kinds that 

 thrive excellently in milk and at the same time produce in it very 

 undesirable changes. A familiar instance is the turnip flavour that 

 butter sometimes possesses. The taste is somewhat sweet, and recalls 

 that of turnips. One of the organisms responsible for this malady is 

 Bacillus foetidus lactis, the individuals of which are rod-shaped and 

 very small, usually about 0*9-1 '5 /z in length, and 0*4-0*6> in breadth. 

 They are normally motile and do not form spores. Other bacteria are 

 known to be able to produce this turnip flavour, but up to the present 

 they have not been accurately described. Artificial souring and absolute 

 cleanliness are obviously the best means of preventing the predominance 

 of this bacillus in the ripening cream. Almost all the other defects of 

 butter can be traced in a similar way to the presence of malignant 

 bacteria. Thus bitter butter is due to fermentative changes in the cream 

 or subsequently in the butter, due to such organisms as Bac. fluorescens 

 liquefaciens, Oidium lactis, and Cladosporium butyri. Again " oily " 

 butter, in which the taste recalls that of mineral oil. is apt to be 

 produced in dairies containing imperfect appliances for keeping the 

 cream and butter at a low temperature. Although the organism 

 causing this change has not been isolated, the change is very probably 

 due to some microbe, for artificial souring is an efficient protection 

 against this malady. Finally, a fishy or train-oil flavour is an evil that 

 butter-makers have to fight against. The cause of it has not yet been 

 discovered, but we may safely conclude that in this case also bacterial 

 action is responsible for the malady. 



3. CHEESE. 



Cheese is prepared by separating caseinogen from the other con- 

 stituents of milk by the use of the ferment rennet. Rennet causes the 



