Assessment of a commercial cross-flow dryer: Impact of grain temperature and moisture content variations on rice quality

After harvesting, rice must be dried for proper preservation. This process causes the formation of moisture gradients within the kernels, which generate tensions that may lead to fissures and subsequent breakage of the kernels during milling, losing commercial value. The Head Rice Yield (HRY), defined as the mass percentage of rough rice that remains at least three-fourth of the original kernel length after milling, is used as a quality parameter of rice. The aim of the present research was to assess the rice temperature across a commercial wood-burning cross-flow dryer. For this purpose, sensors were installed at different points of the dryer to determine temperature variations in the rice. Additionally, the impact of drying rice with different moisture content (MC) on the HRY of two long-grain rice varieties was studied. Grain temperature was not homogeneous along the drying zone and variations were observed as rice circulated in the dryer. In some cases, the grains reached the glass transition temperature, which could increase the grain damage and reduce the HRY. The mixture of paddy with MC differences higher than 1.5% reduced the HRY of Merin rice variety. This effect was not observed in Tacuari variety, suggesting a lower susceptibility to rewetting-induced fissuring, particularly at high MCs.