132 UNIVERSITY OF WISCONSIN STUDIES 
A quicker test is made hy 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 ot two weeks. 
It became our 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 
we accepted the impression from Sayre, Rahn and Far- 
rand? 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 veasts 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 
ect) of these came out poor. But our way selected so few 
good keepers that a vold 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. 
