Design and Processing Performance of a Pilot-Scale Parboiling Unit

Abstract

Abstract. A partially-automated parboiling unit (PU) that can process approximately 2 kg of rough rice per cycle was recently developed and is described. The system components include a stainless steel tank (40-cm long; 20-cm internal diameter), a water-circulation pump, a hot-water supply tank, a steam regulator, four cylindrical sample containers, and a computer interface. The processing performance of the PU was evaluated using rough rice of the long-grain cultivar CL151 obtained from two growing locations. Sample size and location of the sample containers in the tank were the variables considered in the performance tests. The processing conditions were: soaking at 70°C and 138 kPa g (20 psi g ) for 2 h; steaming at 120°C and 69 kPa g (10 psi g ) for 10 min; and gentle drying at 26°C and 65% relative humidity until a moisture content of ~12% was attained. The quality attributes of the parboiled product were compared with those obtained by a laboratory-scale parboiling procedure that employed autoclave steaming. Differences in the percentage of deformed kernels were observed due to the effect of sample size and location of the sample containers in the tank. Milling yields and milled kernel color were minimally affected. In general, the quality attributes of parboiled rice obtained by the PU were either similar or better than those of the product obtained by autoclave steaming. Automated process operations (soaking, draining, and steaming), small sample size requirements, and good reproducibility are some key features that make the PU a valuable tool for rice parboiling and general processing research.