Dynamic Rheology of Rennet Curd

Abstract

Dynamic moduli of rennet curd were measured in a Couette system dynamic rheometer. Shear affected coagulation, resulting in higher firmness shortly after clotting and lower firmness later. Both loss and storage dynamic moduli were frequency dependent in the range of .001 to 10 Hz, but storage modulus was less dependent on frequency. Both moduli show complex behavior as function of temperature with a shallow maximum around 25.degree. C. During gel development at constant temperature, the loss angle at all measured frequencies remained constant throughout a range of 1:100 in total gel strength. Nonlinear regression fitting of gel moduli to the Scott Blair-Burnett model shows good fit but nonrandom residuals. Parameter estimates were biased and depended on which part of the gel strength curve was used. A simple method for estimating the model parameters at the inflection point of the firmness curve is proposed in order to standardize the evaluation and make possible comparison of measurements made with different instruments.