Development and performance evaluation of batch-type cocoa bean dryer

Abstract

Cocoa (Theobroma cacao L.) is a tropical crop, native to Amazon region of South America. The primary cocoa growing regions are Africa, Asia and Latin America. In India, cocoa is mainly cultivated in Kerala, Karnataka, Andhra Pradesh and Tamil Nadu. Cocoa beans from cocoa is the main raw material in the production of chocolates, cosmetics, health drinks etc. Drying is an important step in the postharvest processing of cocoa beans. Cocoa beans are dried from about 60 per cent to about 6-7 per cent moisture content (wb). Currently cocoa beans are dried under sun in majority of cocoa producing countries while the rest uses artificial means. Sun drying produces high quality cocoa beans but the time required for drying is more. Whereas in case of existing artificial drying methods although the drying time is less, low quality cocoa is produced. This report outlines determination of engineering properties of fermented cocoa beans, development of a batch-type cocoa bean dryer, optimization of process parameters and performance evaluation of dryer. The dryer was developed based on the engineering properties of fermented cocoa. The dryer was operated at three different temperatures viz., 40oC, 45oC and 50oC with an air velocity of 2 m/s and a slow agitation of 50 rpm at specific intervals. A known quantity of cocoa beans was sun dried and compared with the mechanically dried cocoa beans. The process parameters was optimized based on physico-chemical qualities of dried cocoa beans such as pH, titrable acidity, free fatty acids, colour, texture etc. and performance evaluation was done based on time required for drying, capacity, efficiency and energy requirement of the dryer. The capacity of dryer was 13.125 kg at 15 cm depth of cocoa beans and 17.50 kg at 20 cm depth. Time required for drying at 40oC, 45oC, 50oC and sun drying was 10, 7, 5.5 hours and 4 days respectively. Efficiency of dryer at different drying temperatures 40oC, 45oC and 50oC was 53.02, 48.47 and 36.80 per cent, respectively. The energy requirement for dryer drying at 40oC, 45oC and 50oC was 16, 11.2 and 8.8 kWh, respectively. Basedon the results, sun dried beans produced highest quality cocoa beans but the duration of drying was too high. Among artificially dried cocoa beans, beans dried at 40oC produced high quality beans in terms of physico-chemical qualities. By considering the dryer efficiency and energy requirement of dryer, cocoa beans dried in cocoa dryer at 45oC with air flow rate 2 m/s and an agitator speed of 50 rpm was selected as optimized parameter.