Dehydration of onion: some theoretical and practical considerations

Summary Yellow globe type onion slices were dehydrated with air at different temperatures and flow rates. Drying‐rate curves were constructed and used for the calculation of critical moisture content, drying constant, effective diffusivity of moisture through the slices and energy of activation for diffusion. Rehydration rates at 25 and 40°C were also determined and found to be independent of drying conditions. An attempt to relate the process of moisture removal to the process of rehydration was made and a possible diffusion mechanism based on the concept of internal and external resistances is discussed.