We describe a pilot-scale drying plant comprising a closed-circuit, ho
t-air convection chamber with a heat pump. In this plant, food and for
est products can be dried with lower energy consumption and over a wid
er range of air, speeds, temperatures and relative humidities than in
conventional driers. Also the drying conditions can be controlled inde
pendently of external conditions. Under several different sets of dryi
ng conditions, we determined the kinetics of drying of grapes that had
been variously pretreated. The effects of drying conditions and the p
retreatment on the drying time and the appearance of the dried product
were evaluated. The drying kinetics can be described by a diffusion m
odel.