Effect of various thermo-hygrometric conditions on the withering kinetics of grapes used for the production of “Amarone” and “Recioto” wines

Grapes of Corvina, Corvinone and Rondinella cultivars used for the production of ‘‘Amarone” and ‘‘Recioto” wines were withered under fixed conditions of temperature (10, 15, 20 and 25 _C) and relative humidity (53%, 75% and 95%) in order to evaluate their withering kinetics in an 80 days time-frame. Withering kinetics were described by means of linear and exponential regression equations. In agreement with basic dehydration theory, withering kinetic rates were found to increase with increasing temperature and with decreasing relative humidity (both above and below the value of the critical moisture). Moisture diffusion coefficients, calculated for each trial condition by solving a simplified equation based on Fick’s second law, varied from 1.63 _ 10_13 to 6.34 _ 10_12. Withering kinetic rates showed an opposite dependence on temperature and relative humidity as shown by multiple linear regression analysis results. Grape surface/volume ratio affected the withering kinetic rates for values above 3.8 cm_1 and at low relative humidity (53%).