DRYING OF AROMATIC RICE IN FLUIDIZED BED DRYER FOLLOWED BY FIXED BED DRYER AND SUN DRYING METHOD

Abstract

Drying and management of aromatic rice (Oryza sativa L.) are important issues because of its increased demand in Bangladesh. Feasibility of two-stage drying of aromatic rice (locally known as Chinigura) and the effects of the drying technique on milling quality were investigated. The milling quality of dried aromatic rice was compared with existing industrial milling results where Louisiana State University (LSU) dryer was used. A laboratory fluidized bed dryer was used for the first stage drying to reduce the initial high moisture content of 22-24% (wb) to 18-19% (wb). A fixed bed dryer and sun drying method were used for the second stage drying for further drying of paddy up to the milling level of 14% (wb) or less. The thicknesses in fluidized bed drying were 8 cm, 10 cm and 12 cm. Three drying air temperatures of 65°C, 85°C and 100°C were applied for each bed thickness. The fixed bed dryer was operated at the temperature of 400C and fixed bed thickness of 30 cm. The tempering of paddy was done at product’s temperature in a closed container for 30 minutes of each dried samples after first stage drying in the fluidized bed dryer. Shorter drying time (4.33 to 4.67 hr) required in application of the two stage drying technique contrast to drying time needed by industrial method (10-12 hours). Two stage drying employing fluidized bed drying and sun drying yielded to 0.6% to 17.35% higher head rice yield than existing industrial drying method. On the other hand, two stage drying with fluidized bed dryer followed by fixed bed dryer gave 4.45% to 14.2% higher head rice yield than industrial drying method. The bed thickness and drying temperature had significant effect on the quality of aromatic rice. On the other hand, milling recovery, whiteness in terms of lightness (L*) and aroma of dried aromatic rice samples were insignificantly varried for all tested samples. Therefore, two-stage drying technique equipped with fluidized bed dryer may be recommended for drying of aromatic rice to save drying time as well as energy.