Comparison between drying characteristics of siganids in a sand-base solar tunnel dryer and a traditional rack dryer

Abstract

Solar dryers are seldom used for fish drying at the Kenyan coast despite abundant sunshine. A sand base solar tunnel dryer was fabricated at Gazi in South Coast, Kenya. The dryer was then used to attempt drying Siganids and its effectiveness measured against that of a traditional rack dryer. The dryer was made using steel, timber, glass, wire-mesh, a solar system with two DC fans, UV treated polythene sheet, coconut fire, sand and black paint. The net drying time of the fish was 30 hours and moisture loss was logarithmic. The starting fresh weight of the Siganids in the solar tunnel dryer was 350 ± 53.0g; by day-one, recorded weight was 165 ± 30.5g, by day-two the weight was 80g ± 17.4 representing a 77.14% loss and 60 ± 21.0g by day-three equivalent to 5.71%. In the traditional rack, the starting fresh weight was 250 ± 50.6g which reduced to 70 ± 44.2g by day-two then to 60 ± 35.5g by day-three equivalent to 4% loss. Drying was discontinued when no further weight loss occurred. There was a significant difference (p<0.05) in weight and moisture loss between the solar tunnel dryer and the traditional rack (p=0.0001, p=0.0038) respectively. The rate of drying was faster in the solar tunnel dryer compared to the traditional drying rack (p = 0.0134). Humidity and temperature varied diversely during drying in the solar tunnel dryer with humidity reaching 22-28% while temperatures ranged from 60-69°C. In the traditional rack, humidity was constant during peak heat drying periods at 60-70% with temperatures of 30-33°C. Lower humidity and higher temperatures inside the solar tunnel dryer caused the faster drying rates. The fish in the solar tunnel dryer attained a final moisture content of 17.9%. No insect infestation was curtailed by design when using the solar tunnel dryer. It is concluded that the solar tunnel dryer is more effective in drying fish than the traditional drying rack. There is no insect infestation during drying in the solar tunnel dryer and the fish is dried to a low moisture content in the solar tunnel dryer which is more suitable for longer storage. It recommended that fish processors at the beach start migrating to adopt solar drying technologies to reduce drying time, get fish that can be stored for a longer time due to lower moisture content.