The article presents a grain-scale experimental approach for the study of a model that swells granular food material. During the swelling phase, both the evolution of particle size using image analysis and the spatially resolved field of diffusion coefficient of water inside the grains were studied using MRI measurements. A concentrically penetration of water in the cross section of the grains was shown on images. The experimental results were compared to classical models from the literature used to predict the swelling of polymeric materials. A simple first-order kinetic equation was shown to be adequate to describe the size evolution during swelling. Thus, the results suggested that the swelling dynamics was a water uptake-limiting mechanism because of the existence of a gelatinous layer at the grain surface formed during the manufacturing process, as previously reported in the literature.