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The Relationship Between Fat Content of Fresh Milk and its Apparent Acidity

University of Arizona, College of Agriculture, Tucson, Arizona

ABSTRACT

Data are presented herein which show that milk in general increases in apparent acidity as the fat content increases up to 6 per cent butterfat, from this point on the acidity decreases. This phenomena was also noted in milk taken from Holstein cows exclusively and from Guernsey cows exclusively, but it was not so apparent in Jersey milk. Individual cows likewise did not show this variation. As summer conditions became prevalent, the mean titratable acidity of milk in general decreased. Milk from the morning milking did not display the same trend in variation in acidity that was displayed by milk from the afternoon milking.

A small number of cows tested showed abnormal tests at all times. Two animals producing milk which was always abnormally low in acidity and one cow produced milk that was always abnormally high in acidity.

Cows advancing in their lactation period and sick cows produced milk abnormally low in acidity. Cows after freshening, for a period of about 30 days, produced milk abnormally high in acidity.

On the basis of this study the author is inclined to agree with the conclusions of Fleming and Nair (5) namely that the ease of application of the acidity test and its reliability warrant its continued use until some better test is found and that it does not normally work an injustice on the producers of even the richest milk. The author urges, however, that users of the titratable acidity test adopt a limit of acidity at which milk will be acceptable that varies directly as the fat, increasing the limit .01 per cent for every 2 per cent increase in fat content up to 6 per cent. For example, a standard for 2 per cent milk could be set at .17 per cent acidity, for 3 per cent milk at .175 per cent acidity, .18 per cent for 4 per cent milk, and .19 per cent for 6 per cent milk, or any other standard which they might choose as being suitable for their conditions.

The recommendations of Sommer and Hart (6) are also heartily approved of as being worth-while steps to take in the case of consistently high acid milk.