Rheological Aspects of the Renneting of Milk Concentrated by Ultrafiltration

The kinetics of clotting by rennet of ultrafiltrated milk were studied by determining induction and clotting times, and development of the rigidity modulus as a function of rennet concentration and protein content in the sample. Creep cmpliance‐time studies were conducted on the resultant gels at three different stresses. Clotting time increased with protein content and decreased with rennet concentration. The protein effect on clotting time decreased with increasing rennet concentration and was practically nil at 200 mg enzyme/kg sample. The ultimate rigidity and the viscoelastic parameters of gels depended on the protein concentration in a double logarithmic relationship. The calculated values of the constants indicated that the viscosities were influenced to a greater degree by the protein concentration than were the elastic moduli. The renneted milk gels exhibited creep compliance‐time response at low shear stresses indicative of the viscoelastic behaviour of an interlinked three‐dimensional network. Gelation followed a second order reaction in its initial stages and an approximately third order reaction in the final stage. The results are discussed in terms of potential mechanism and type of bonds involved.