Two stage drying of high moisture paddy with intervening rest period

The artificial methods of paddy grain drying have an effective influence on energy consumption and its quality. The effects of intervening rest periods between the two stages of drying on drying rate, energy consumption and head rice yield were evaluated. During the period of the rest stage, the grain released moisture as an effect of the residual temperature, and also, the grain moisture became uniformly distributed within the kernels. The appropriate moisture ratio at which resting starts and the duration of resting were evaluated by measuring the changes in relative humidity in the head space of the mass of paddy and also from the diffusion coefficient values obtained from the drying rate data. A resting duration between 75 and 90 min at a moisture ratio around 0.715 was found suitable for overall good results in respect of drying, energy consumption and head rice yield. Using the measured moisture data of the first stage, rest period and second stage, a non-linear regression method was applied to an approximate solution of the diffusion equation to estimate the drying rate and, further, the effective diffusion coefficient. A significant amount of energy (21–44%) could be saved by providing a rest period from 30 to120 min between the two stages of drying. Discontinuing the drying process during the rest period above 60 min considerably improved the head rice percent when compared with the results from continuous drying experiments.