Coagulum Formation - Milk coagulation occurs due to two distinct activities.

(i) Inoculation with bacterial cultures, e.g., Streptococcus lactis or S. cremoris for incubation at 31°C, or S. thermophiles combined with Lactobacillus lactis, L. bulgaricus or L. helveticus (for incubation at 50°C), results in lactose degradation to produce lactic acid, which lowers the pH to about 4.6.

(ii) Incubation with rennet cleaves ҝ-casein into para- ҝ -casein and caseino macropeptide. This cleavage occurs at a specific peptide bond between phenylalanine at position 105 and methionine at position 106 (-phe 105-met 106-), and leads to coagulation of α and β -caseins and the ҝ -casein hydrolysis products.