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The Correlation Between Organisms Found Micro-Scopically in Butter Serum and the Grade of Cream from which the Butter was Made

Montana State College

ABSTRACT

The data recorded in the study consisted of sample number, cream score, criticisms of flavor, appearance of the cream slide, and appearance of the stained butter serum.

In the preliminary work 130 samples were studied for the purpose of determining the microscopic appearance of the butter serum. This information was correlated with each of the four grades of cream from which the butter was churned. The grades of cream used in making the butter were "excellent" scoring 93 or above, "good"
to
, "fair" 90 to 91, and "poor" below 90 in score.

The stained slides of 524 samples of butter were studied under the microscope and the grade of cream predicted. Of these 524 samples, 143 were from the "excellent" group and 131 (91.6 per cent) were given the correct grade. In the "good" group there were 125 samples. Seventy-three (58.4 per cent) were accurately graded. One hundred and fifty-nine samples of the "fair" group were examined and 68 (42.7 per cent) had the right grade predicted. In the last group 52 (53.6 per cent) of the 97 "poor" group samples were graded accurately. This seems to indicate that the microscopic examination was fairly accurate in distinguishing butter made from "excellent" cream, but for lower grades it was not a reliable method.

Storage periods of 1 to 3 days, 7 days, 14 days, and 30 days did not materially influence the number of grades determined correctly. This was verified by a trial in which one-half the samples was held for 1 to 3 days and the remaining samples 30 days. The percentage determined correctly from 103 churnings was the same (62.2) for both storage periods.

The presence or absence of culture organisms did not effect the microscopic grading.

The results on studies of the "fair" group indicated samples from commercial churnings were slightly more difficult to grade correctly than those from the laboratory procedure. This was apparently caused by the difference in handling conditions.

The two apparent reasons for not being able to determine the "good," "fair," and "poor" grades as accurately as the "excellent" grade were: (1) Low scoring cream was not always the result of bacteriological action but was caused by chemical action and absorbed feed flavors. (2) The other reason was the contamination by organisms subsequent to pasteurization of cream and during the churning process.