Effect of Grain Inverters in Cross-Flow Dryers on Kernel Fissuring and Head Rice Yield Reduction

Abstract

HighlightsGrain inverters minimized fissuring of rice kernels closest to the heated air plenum at plenum air temperatures =55°C.Grain inverters had no effect on rice kernel fissuring across a grain column at plenum air temperatures <55°C.Grain inverters decreased head rice yield reduction of samples dried at plenum air temperatures >55°C but had no effect on head rice yield reduction at plenum air temperatures =55°C.One or two grain inverters in a cross-flow dryer can help reduce kernel fissuring and minimize head rice yield reduction.Abstract. Industrial-scale cross-flow dryers are commonly equipped with grain inverters to facilitate uniform drying across the column thickness, but limited information is available on the effect of grain inverters on rice milling quality. In this study, lab-scale drying experiments were performed to investigate the effect of grain inverters on kernel fissuring and head rice yield reduction. Rice samples of long-grain cultivar Roy J were dried for 60 min at plenum air temperatures of 45°C, 50°C, 55°C, and 60°C. The number of grain inversions during a 60 min drying period were 0, 1, and 2. After drying, a portion of the sample was tempered at a final bulk-rice temperature (heated tempering), while the other portion was tempered at ambient room temperature (ambient tempering). At plenum air temperatures of 55°C or 60°C, grain inversion (1 or 2 inversions) minimized fissuring of kernels closest to the heated-air plenum compared to 0 grain inversion. At 45°C and 50°C, grain inversion did not affect kernel fissuring. Similarly, at plenum air temperatures greater than 55°C for both ambient tempering and heated tempering approaches, 1 or 2 grain inversions significantly minimized head rice yield reductions compared to 0 grain inversion. These findings may be valuable for designing cross-flow dryers by informing decisions on the number of grain inverters needed to reduce fissuring and minimize head rice yield reduction. Keywords: Column dryer, Milling yields, Reversed airflow, Rice quality, Tempering, Turnflow, X-ray imaging.