Infrared and hot-air-assisted microwave heating of foods for control of surface moisture

Temperature and moisture profiles for infrared and hot-air-assisted microwave heating of food were studied using a multiphase porous media transport model for energy and moisture in the food. Microwave-only heating results in surface moisture build-up due to enhanced (pressure-driven) flow of moisture to the surface and the cold ambient air's inability to remove moisture at a high rate. For foods in which infrared energy penetrates significantly, addition of infrared actually increases the surface moisture build-up. When absorbed mostly on the surface, infrared can reduce surface moisture and, beyond a threshold power level, it can reduce the surface moisture to lower than its initial value. Hot air also can reduce surface moisture and increase surface temperature, but not as effectively as infrared heat, perhaps due to a much lower surface heat flux for hot air compared to the infrared energy. Increasing air velocity and therefore the heat and mass transfer coefficients can eliminate the accumulated surface moisture. (C) 2002 Elsevier Science Ltd. All rights reserved.