Microscope observations gave evidence of the coffee bean structure heterogeneity, whereas, coffee bean isotherms of different parts of grain show not significant difference excluding the parchment. Diffusion tests allowed determining the relationship between the diffusion coefficient and the water content. Therefore we propose an original method to determine the water transfer resistance in different parts of grain including the parchment. The set of results will permit to simulate a coffee grain drying and to have information about the zones at high water activity. This information would help to diminish the risk of fungus development.