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Curd Tension of Milk and its Relationship to Fimness of Curd in Cheesemaking

Bureau of Dairy Industry, U. S. Department of Agriculture, Washington, D. C.

ABSTRACT

In experiments on over 300 samples of milk the following observations were made:

The Hill curd test was found not satisfactory for determining the firmness of curd in milk to be used for making cheese. The rennet curd tension as measured by means of the Hill Curd-O-Meter was entirely suitable for this purpose, and the determination of rennet coagulation time was fairly satisfactory.

The pH values of milks bore a very definite relation to the rennet coagulation time and to the rennet curd tension, and bore a less definite relation to the Hill curd tension. The pH seemed to be a major factor in influencing the rennet coagulation time, while the percentage of casein was found to be more important in influencing the rennet curd tension.

Milks stable to rennet were usually stable to alcohol. Stability to both rennet and alcohol was increased when milk was stored at 2° to 52° C. for from a few hours to several days. Stability to both rennet and alcohol was decreased by the addition of CaCl₂.

Homogenization markedly decreased the rennet curd tension of whole milk but did not change that of skimmilk; this process did not change the rennet coagulation time of either whole or skimmilk. Removal of milk fat by separation increased the rennet curd tension and caused a slight increase rather than a decrease in the rennet coagulation time. These observations lead'to the conclusion that the curd-softening effect of homogenization is due principally to an increase in the dispersion of the fat, the dispersed fat acting as a physical hindrance to the aggregation of the casein molecules and micellae.

Pasteurization caused a noticeable softening of milk curd and caused a slight increase in rennet coagulation time.

The presence of mastitis caused an increase in pH, an increase in rennet coagulation time, and a decrease in rennet curd tension.