A lot of food industries are producing legumes such as bean and chickpea. Soaking which is diffusion of water in them is usually one of the processes in the production line before cooking. In this study, it is experimentally investigated the water diffusion on red beans as a function of time and temperature, and then the influence of this diffusion on the cooking time and the final volume of cooked legumes in different temperatures. Thus, the energy management and final volume of the production could be optimized with respect to the cooking time, cooking temperature and the duration of water diffusion and temperature condition of soaking before the cooking process. Also in the present study, volumetric water diffusion is defined for legumes, that is a function of the diffused water, the initial volume (before soaking) and final volume of the productions (after cooking). The results confirm that the final volume of the product and the cooking time are a function of the conditions of the water diffusion before cooking.