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The Effect of Certain Factors upon the Keeping Quality of Butter

Laboratory of Bacteriology, New York State College of Agriculture, Cornell University, Ithaca, New York

ABSTRACT

The effect of natural milk enzymes, bacteria, acid, and salt upon the keeping quality of butter held at temperatures which might permit the growth of bacteria, has been studied.

Five series of butter consisting of five hundred seventy-six samples, made and held under known and carefully controlled conditions, have been examined.

The results obtained and the data presented seem to justify the following conclusions:

1. Pasteurization of cream at 165° F. (73.9° C.) for 30 minutes destroys most, if not all, of the harmful natural milk enzymes.
   
2. All milk enzymes harmful to the keeping quality of the butter were not destroyed by pasteurization of the cream at 145° F. (62.8° C.) for 30 minutes.
   
3. The action of milk enzymes in butter was retarded little, or none, by salt.
   
4. The action of milk enzymes in butter was definitely inhibited by pH 4.7, or less.
   
5. None of the non-spore-producing bacteria, found to be of importance in the spoilage of butter, were able to survive 165° F. (73.9° C.) for 30 minutes.
   
6. In the absence of other spoilage factors, a direct correlation seems to exist between the number of fat splitting and casein digesting bacteria and the keeping quality of the butter.
   
7. The well known inhibiting action of acid and salt upon the growth of bacteria in butter was confirmed.
   
8. The presence of either acid or salt in butter, not containing other spoilage factors considered in this study, resulted, after storage, in a poorer quality butter.
   
9. The combined deteriorating effect of both acid and salt was shown.
   
10. As would be expected, all butters examined spoiled more rapidly at the higher holding temperatures.