A simple model for dehydration of onion pieces is presented to take into account the change of interfacial surface area undergone by the samples as drying proceeds, as well as the different water removal rates through surfaces of different characteristics. It is assumed that the drying rate is linearly proportional to the instantaneous water content whatever the surface involved; either the natural boundaries of the leaves (cataphila) or those produced by cutting them normally along the main dimension. Numerical integration of the instantaneous rates allows the calculation of water removed during a given time and, conversely, the drying time required to reduce the water content to a given extent as a function of the sample size. This information is relevant in order to design the cutting technique which would produce particles of adequate size for practical drying.