Solar Dehydration of Sliced Onion

Abstract

Post-harvest loss of onion (Allium cepa L.) can be reduced by using proper drying techniques. A small-scale solar dryer for dehydration of sliced onion was designed, constructed, and operated at the South China Agricultural University Workshop, Guangzhou, China. The principal components of the dryer were two solar air collectors, a drying unit, and an air-handling unit. The solar dryer was used to dehydrate onion sliced into 3-mm-thick rings during 17 to 19 Dec. 2000 to reach the safe storage moisture content. The drying procedure used air heated to 30.1°C, 59.3% relative humidity, at a 0.05 m3.s−1 air flow rate. The duration of drying averaged 20.2 h, which reduced the initial 83% moisture content to a final 5% moisture content. The solar dryer accelerated drying 2.3-fold over open-air sun drying. The area needed for solar drying was about 25% that of the ground required for equal air drying intensity.