Seventy boxes of salted Victorian butter were held at 12° F. for three months. Bacteriological and chemical examinations were carried out before and after storage in order to observe the changes which occurred and the factors which controlled deterioration.
The bacteriological examination showed that on the average only slight changes in bacterial numbers occurred during the actual cold storage period. None of the bacterial, yeast or mould counts revealed any positive association with keeping quality.
The catalase test gave negative results. It is suggested that enzyme activity is not an important factor in controlling deterioration of the butters.
The chemical examinations indicated that the variations in curd or salt content did not affect keeping quality. Fat hydrolysis, as measured by ether soluble acidity of the fat, and fat oxidation as measured by peroxide value, did not appear to be important factors in deterioration. Considerable variations were observed in the acidity of butters made from cream supposed to be “neutralised” to the same acidity. Acidity of the butter as measured by titration of water-soluble material was closely related to the pH of the butter. Butter acidity and copper content appeared to be the most important factors controlling keeping quality. The mechanism by which acidity causes deterioration was not revealed by the investigation.