The influence of various factors on milk clotting time

Department of Food Technology and Biochemistry, Faculty of Agriculture, Belgrade-Zemun (1,2,3)


The influence of pH (6.5 and 5.8), amount of added CaCl2 (0, 200 and 400 mg/l)), coagulation temperature (30ºC and 35ºC) and heat treatment of milk (65ºC/30 min and 87ºC/10 min) on the rate of rennet induced milk coagulation (s) were investigated. The time (s) from rennet addition to onset of gelation (as indicated by the first visible floccules) was measured. The milk samples heat-treated at 87ºC/10 min, with 400 mg/l added CaCl2, which were coagulated at 35ºC and pH 5.8, coagulated 23.28-fold faster than the same samples without added CaCl2, which were coagulated at 30ºC and pH 6.5. The results of investigations related to the influence of particular coagulation factors on the coagulation rate of heat-treated milk showed that at pH 6.5 the most pronounced influence was demonstrated by the amount of Ca2+ and temperature of coagulation. At pH 5.8, different amounts of Ca2+ and used temperatures of coagulation did not influence coagulation rate regardless of the used heat treatment of milk. The influence of used heat treatment of milk was particularly pronounced during coagulation of samples without added CaCl2 that coagulated at 30ºC and pH 6.5. The used heat treatment of milk practically did not influence the milk coagulation rate at pH 5.8. The greatest influence on milk coagulation rate was showed by pH. This influence was the most marked in coagulation of samples in which the coaggregates were formed, regardless of the amount of added Ca2+ and used coagulation temperatures.

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