A method using a turbidity sensor has been developed to study rehydration of dairy powders. The process involved dispersing powder in a stirred vessel equipped with a turbidity sensor under standardized conditions. The changes of turbidity Occurring during powder rehydration highlighted several stages including particles wetting, then swelling as the water penetrates into the powder bed, followed by a slow dispersion of the particles. The following information was obtained: wetting time (Tw), swelling time (Ts) and rehydration time (Tr). The results are in agreement with static light scattering and optic microscopy analyses. Finally, the method was used for the characterization of two powders (native phosphocaseinate and whey proteins isolate) differing in their rehydration properties. (C) 2008 Elsevier B.V. All rights reserved.