The Heat Stability of Evaporated Milk Made from Hard-Curd Milk, Soft-Curd Milk and Milk from Mastitis Infected Udders

In the course of some preliminary studies with soft-curd milk, it was found that the milk samples of low curd tension, after condensing, consistently coagulated at lower temperatures or coagulated sooner at the same temperature than did milk of high curd tension. The soft-curd product was furthermore affected erratically by added salts such as calcium acetate, sodium citrate and sodium carbonate whereas the hard-curd milk was invariably further stabilized by the citrate and carbonate and destabilized by the acetate. These results were at first interpreted as indicating some inherent qualitative difference between soft-curd milk and hard-curd milk but this conclusion was soon abandoned since exhaustive study failed to reveal such differences between the two types of milk (1). I t was found, however, that udder infections lower the curd tension of some milk sufficiently to bring it under a soft-curd classification (2). I n checking on the samples of milk used for the comparisons mentioned above, it was discovered that the soft-curd milk came from a group of cows, several of which reacted positively to mastiffs in one or more udder quarters. I t was therefore decided to repeat the comparisons using hardcurd and soft-curd milk from animals free from suspicion of udder infections and milk from animals showing sub-clinical indications of mastitis in one or more quarters as determined by the cell count, the thybromo~ test, and the precentage of clflorides.