Study of Relating Drying Time and Drying Rate Constant (K) to Dryer Parameters and Milling Loss (Breakage) of Rice

The Drying process is one of the most important factors which are effective on the milling quality of rice and its economic value. In order to investigate the effect of dryer parameters on milling quality of rice and their relationships, one of the usual rice varieties (Binam) of Gilan province with an average milling quality and the initial moisture content of 20.5% was selected. Drying process was performed on the basis of a complete randomized design with 20 treatments and 3 factors including temprature (at five levels of 30, 40, 50, 60 and 70 °C) , air velocity (at two levels of 0.5 and 2 m/s) and final moisture content of paddy (at two levels of 10.5% and 14% on wet basis equal to 11.7% and 16.3% on dry basis respectively). Results of the experiments indicated that increase of temprature or air velocity reduces drying time but increases drying rate constant (K). It also revealed that decrease of final moisture content of paddy increases drying time significantly, but doesn’t have any significant effect on drying rate constant (K). Correlation test indicated that milling loss (breakage) has a negative relation to drying time and a positive relation to drying rate constant(K), however, bending strength has a positive relation to drying time and a negative relation to constant of K. Regression of qualitative properties of paddy including: milling loss (breakage) and the bending strength over drying time and constant of K revealed that drying time is a better criterion for predicting the mentioned qualitative properties.