A mathematical model was developed to quantitatively analyze the rheological data of rennet casein gelation at different cooling rates. Kinetic parameters were estimated and correlated with the microstructure development of the protein network. The kinetic model identified structure development upon cooling to be first order, and the network forming energies were estimated for four protein concentrations cooled at four rates. A lower energy for network formation was observed for a slower cooling rate and a higher protein concentration. This observation resulted from the availability of more floes at a slower cooling rate and a higher casein concentration, simplifying floc cross-linking. By analyzing the kinetics during the aging process of casein gels, no difference in the reaction mechanism was observed. This study illustrated that structure formation resulted from the addition of flocs into the protein network: not all flocs were part of the network at a defined gel point. The incubation period following cooling integrated idle flocs into the network, thereby strengthening the gel. By understanding the gelation mechanism during cooling of rennet casein gels, the structure and thus quality of dairy products, such as processed cheese, may be better controlled. (C) 2004 Elsevier Inc. All rights reserved.