Viscosity changes during rennet coagulation of Murciano‐Granadina goat milk

The viscosity changes during coagulation of raw and pasteurized Murciano‐Granadina goat milk with 10 rennets and coagulant enzymes were studied using a cylindrical rotational viscometer. The effect of three shear rates (7.32, 14.68, 73.42 s‐1) was analysed in reconstituted milk using 60% chymosin rennet and different enzyme concentrations. The shear rate selected (14.68 s‐1) corresponded to that in which the coagulation time was not modified. At a sheer rate of 73.42 s‐1 there was a significant difference (p < .05) in the milk clotting time determined compared with the shear rates of 7.32 and 14.68 s‐1. At the beginning of the coagulation process there was a decrease in the viscosity value, which was higher in raw milk (22%) than in the two heat treated samples (17% in milk pasteurized at 65°C for 30 min, low temperature long time, and 19% in milk pasteurized at 75°C for 15 s, high temperature short time). After this period the viscosity rose rapidly and reached a value 2.89 times greater than at time 0. A highly significant Pearson correlation (0.952‐0.994) was found between the coagulation time determined by the Berridge method and viscometric measurement in raw and pasteurized milk.