A rheological approach to the study of concentrated milk clotting

The aim of the present work is to analyze the complex phenomena involved in the concentrated milk clotting process in order to define general criteria applicable to the design of a continuous coagulator. A full characterizati on of the rheological properties of completely hydrolyzed milk as a functio n of two different parameters, i.e., the coagulator temperature and the con centration degree of the milk, is presented. The dynamic evolution of loss, G", and storage, G', moduli has been obtained at different frequency value s and for different concentration degrees during the clotting process. Time cure tests have been performed on completely hydrolyzed milk samples showi ng that the rate of curing is very high and that the time for rheological e xperiments is much too short for testing Winter's theory of gelation. To ov ercome this problem, the intersect of loss and storage moduli was used for estimating the coagulation. Coagulation is faster when higher temperatures are used and the consistency of the final curd is greater if a more concent rated milk is used. A tentative physical explanation based on the network t heories is presented. If an observation time far enough from the crossover point is chosen it can be seen that the curd strength estimated at 40 degre esC is about. 50 times higher than that one evaluated at 25 degreesC. Among the considered temperatures, a good processing value was evaluated at 40 d egreesC.