Grape drying in a pilot plant with a heat pump

We describe a pilot-scale drying plant comprising a closed-circuit, hot-air convection chamber with a heat pump. In this plant, food and forest products can be dried with lower energy consumption and over a wider range of air, speeds, temperatures and relative humidities than in conventional driers. Also the drying conditions can be controlled independently of external conditions. Under several different sets of drying conditions, we determined the kinetics of drying of grapes that had been variously pretreated. The effects of drying conditions and the pretreatment on the drying time and the appearance of the dried product were evaluated. The drying kinetics can be described by a diffusion model.