BUTTER DEFECTS 485 



the metallic salts on the ingredients of the cream and possibly 

 enhancing also bacterial and enzyme action. Furthermore, in 

 most vats several metals are exposed to the cream, so that it is 

 not improbable that this bimetallic submersion in the acid of the 

 cream, gives rise to a slight galvanic current, producing electro- 

 lytic action which naturally hastens the formation of metallic 

 salts. 



Finally, the churning of cream with a high acid content 

 augments the acid content of the resulting butter and this 

 furnishes an additional essential factor in the combination of 

 conditions which cause metallic flavor. 



Attempts to attribute the metallic flavor to the presence 

 in the cream of specific bacteria or groups of microorganisms 

 experimentally, have proven abo'rtive. While bacteria, through 

 their power to decompose portions of the ingredients of cream 

 and butter, forming acid and other cleavage products, may 

 assist to a limited extent in the production of metallic flavor, 

 they cannot be considered as the specific cause of this defect. 



Nor is the fact that the metallic flavor often does not appear 

 in the fresh butter, but develops after a considerable period of 

 storage, necessarily indicative of bacterial origin. A careful 

 study of the available data dealing with the causes of this but- 

 ter defect emphasizes the complexity of the combination of 

 factors and conditions responsible for the metallic flavor and 

 the wide variations in the rapidity with which this defect de- 

 velops. On the basis of the bulk of evidence it appears reason- 

 able to attribute metallic flavor to chemical action. 



Prevention of Metallic Flavor. According to our present 

 limited lights on this subject, the most consistent means to 

 prevent metallic flavor in butter is : 



1. To use rust-free cream shipping cans and to return to 

 the farmer cans only that are clean and properly rinsed and 

 steamed and thoroughly dried. 



2. To keep forewarmers, pasteurizers, coolers, vats, etc., 

 well tinned, to thoroughly scour exposed copper surfaces, keep- 

 ing them bright and free from verdigris, and to flush the entire 

 system each day before use with hot water, thus removing any 

 water it may contain and which may have absorbed metallic 

 salts. 



