BUTTER DEFECTS 495 



ture of cold storage and the shorter the time that elapses be- 

 tween manufacture and cold storage, the longer will the butter 

 generally retain the desired aroma and flavor of fresh butter. 



The exact cause of this flavor and the nature of the decom- 

 position products responsible for it have not been conclusively 

 demonstrated. Experimental data suggest that this flavor is 

 principally due to spontaneous chemical changes, in which 

 oxidation plays an important part and that this oxidation is 

 accelerated by the presence of catalyzers in the form of metallic 

 salts. Butter made from a poor quality of cream, such as cream 

 that has yielded excessively to fermentation and that is of high 

 acidity, develops storage flavor and its derivatives most rapidly. 

 It is not improbable also that the storage flavor represents a 

 forerunner, or early stage, of other off-flavors which under favor- 

 able conditions may supersede it in the form of metallic flavor, 

 or fishy flavor, etc. 



Rancid Flavor. Rancidity is fa very common and Well 

 known butter defect. The rancid or strong flavor is a charac- 

 teristic infirmity of old butter. When present to a pronounced 

 extent in butter, such butter is no longer salable as "eating" 

 butter and generally has to be disposed of as packing stock 

 at a great sacrifice in price. 



Cause of Rancid Flavor. Rancidity is a flavor and odor de- 

 fect that is due to decomposition of the butterfat. It is char- 

 acteristic not only of spoiled butter or butterfat, but is a common 

 decomposition product of all fats and oils, animal and vegetable. 

 The chemistry of the reactions yielding rancid flavor and odor 

 is not well understood, though it has been the subject of ex- 

 tensive investigations for many years. 



In the case of butter, rancidity, and especially the initial 

 phase of rancidity, appears to be due to hydrolysis of the butter 

 fat, which splits the glycerides of the fats into free fatty acids 

 and glycerol. This hydrolysis is in all probability due very 

 largely to bacterial and mold action, since the casein and lac- 

 tose contained in butter furnish the food elements necessary for 

 the bacteria to thrive on. 



The hydrolysis of the fat leading to rancidity, however, is 

 not necessarily dependent on micro-organisms. It may be 



