To overcome the nonideality of the model presented by Hsu, who assumed that soybean grains suffered no change in volume during hydration, a distributed parameter model was developed following an approach similar to that used by Hsu, but considering that the grain volume varies as a function of hydration time. This new model presents more complex numerical solution and it was compared with the original Hsu model at constant volume. The models were fitted to experimental measurements of moisture content of soybean grains over time by the least squares method. The results showed that the volume of soybean grains increased 30% from the beginning to the end of hydration and the effective diffusivity values of the variable volume model were about ten times larger than those obtained from the Hsu model, indicating that the hypothesis of constant volume adopted by Hsu is unrealistic and leads to considerable errors in the estimation of effective diffusivity of water in soybean grains. In addition, an analysis of the behavior of the effective diffusion coefficients as a function of temperature and moisture content was performed. (c) 2012 Elsevier Ltd. All rights reserved.