MILK CLOTTING AND CURD FIRMNESS AS AFFECTED BY TYPE OF MILK-CLOTTING ENZYME, CALCIUM-CHLORIDE CONCENTRATION, AND SEASON OF YEAR

Firmness of milk gels formed with rennet, a mixture of rennet and porcine pepsin (Chymoset), and proteases from Mucor miehei and Mucor pusillus were measured with an apparatus which imposes an oscillatory motion to milk during clotting. This causes the clotting milk to create an oscillating pressure against a sensing diaphragm; the extent of pressure varies directly with clot firmness. No differences in rates of firming were significant between gels formed by the various enzymes in milk at pH 6.5 and 30 C and at pH 6.7 and 34 C. Gels formed by Mucor proteases at the extremes of experimental conditions (pH 6.7, 30 C and pH 6.5, 34 C) firmed less rapidly than gels formed by the other enzymes. Adding calcium chloride to milk reduced clotting time and increased rates of firming of gels formed by all enzymes tested. Clotting times of milk treated with rennet did not vary markedly at various seasons, but rate of firming of clots formed from milk in June was much slower than clots formed at other periods of the year. The time required for initial clot formation and subsequent rate of firming were affected differently by deviations in type of enzyme, pH, and temperature of milk, calcium2+ concentration, season of year, and interactions of these factors. © 1979, American Dairy Science Association. All rights reserved.