TAINTS AND DEFECTS OF BUTTER 353 



The recent researches of Reinmann and Jensen have 

 shown that rancidity is mainly the work of aerobic 

 bacteria and fungi, conditioned by the presence of air, 

 moisture and the other factors already mentioned. Its 

 full development is associated with a number of different 

 chemical reactions which occur among the decomposition 

 products of the fats, caseinogen, and milk-sugar ; the 

 changes are not quite so complex, perhaps, as those 

 which take place in a ripening cheese, but are in many 

 respects analogous to the latter. 



There is much evidence to support the view that 

 micro-organisms are chiefly responsible for the initiation 

 and maintenance of the changes involved. A sample 

 of normal butter containing a considerable amount of 

 casein, sugar, and other materials upon which bacteria 

 thrive becomes rancid much more rapidly than a speci- 

 men containing a smaller quantity of these compounds. 



Butter made from sterilized cream keeps fresh for a 

 long time, in spite of the fact that it contains an 

 abundant supply of food for bacteria ; however, when 

 inoculated with a small piece of rancid butter, the whole 

 becomes rancid very quickly. 



Antiseptics, such as salicylic acid and formalin, check 

 it, and keeping the butter in a cool place tends to prevent 

 it. That the change is not entirely due to enzymes is 

 deduced from the observations that antiseptic agents 

 which allow these to act, but check the chemical activity 

 of living organisms, stop the development of rancidity. 



No single species of bacterium or fungus which has 

 been isolated from rancid butter has been found capable 

 of inducing the rancid taste and flavour in a sterile 

 sample. The production of this objectionable taint is 

 the result of the interaction of several kinds of organisms 

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