132 UNIVERSITY OF WISCONSIN STUDIES 



A quicker test is made by storing small samples at 60 

 to 70 F. A very poor keeper develops a bad flavor within 

 three days. A good keeper, such as is usually made, scores 

 89 to 90 at the end of two weeks. 



It became onr problem to ascertain the cause of poor keep- 

 ing and to find a remedy for it. Bacteriological philosophy 

 of the keeping quality of butter has exerted an exaggerated 

 influence in every sphere of butter-making. For a time 

 Ave accepted the impression from Sayre, Rahn and Far- 

 rand 1 that only yeasts can tolerate the well nigh saturated 

 solution of salt which is the watery part (brine) of butter. 

 To our disappointment, we did not find any connection be- 

 tween yeasts and a very long and serious epidemic of fishy 

 butter. Never present in great numbers, sometimes absent, 

 they practically did not multiply in the course of time. 



At the beginning of 1913 we thought that by ascertaining 

 the number of yeasts and Oidia (lactis) in butter we could 

 foretell its keeping quality. We made a study of the cold 

 storage of 177 lots of butter from a number of states. As 

 the butter went into cold storage, the commercial judge made 

 his predictions according to the quality of the butter and 

 previous experience with the creamery. We predicted from 

 the number of yeasts and Oidia. At the end of the storage 

 season the predictions were compared with the final quality 

 of the butter. We predicted that 39 lots would keep well. 

 Only five (13 per cent) of these kept poorly. The judge pre- 

 dicted that 83 lots would keep well. Twenty-four (29 per 

 cent) of these came out poor. But our way selected so few 

 good keepers that a cold storage could not have made a living 

 by our method. 



We now know that under American creamery conditions 

 keeping quality is due to acidity, elimination of buttermilk, 

 pasteurization, and proper working. The deterioration of 

 butter is mainly the result of physical or biochemical causes. 

 An indirect part may be played by micro-organisms. 



These bacteriological attempts taught us how to make counts 

 of yeasts and Oidia. We found that vatfuls and churnfuls 



1 Technical Bulletin, No. 1, Michigan Experiment Station. 



