EXPERIMENTAL STUDY ON THE QUALITY OF ROUGH RICE RELATED TO DRYING CONDITIONS

The published literature reviews various factors responsible for breakage of rice during processing. The proportion of immature and cracked grains, which is a function of the harvesting and drying conditions, has been well established as having a strong influence on breakage. The effect of moisture gradients during water adsorption or desorption cycles has also been described. The purpose of this study is to examine the dynamic influence of the drying process on the final quality of rice kernels. Variables investigated are drying temperature and air relative humidity. The criteria chosen for evaluating the quality of rice is the measure of the mass percentage of head rice after processing on a rice processing pilot unit. The influence of a thermal shock has been studied. The results show no loss of quality due to thermal gradients if paddy is exposed to temperatures between 30°C and 90°C without drying. On the other hand, drying at ambient humidity in the same conditions of air temperature as above leads to a rapid increase of the percentage of broken kernels. This proportion increases with the drying rates. This confirms the influence of humidity gradients on the evolution of mechanical quality. An experimental design was built to quantify the influence of temperature and evaporating capacity of drying air on the evolution of quality of paddy during drying.