Development of an intermittent solar dryer for cocoa beans

Abstract

A solar dryer with thermal energy storage was developed for intermittent drying of cocoa beans. The prototype was built using readily available local materials. Drying mechanism was based on a combination of convective heating and direct radiation, with a provision for controlling the rate of airflow through the beans. The experimental model dehydrated cocoa beans from 53.4 to 3.6% moisture content (wb) in a 72 hours inter-mittent drying process against ambient temperature and relative humidity in the range 25-30 o C and 58-98%, respectively. Quality assessment of the dried beans showed that beans of good quality attributes: pH of 6.35, acid value of 3.40 mg/g, with mildly bitter taste were obtained under free convective drying; whilst, increase in moisture re-absorption and acidic flavour were indicated with forced convective drying. The work, thus, provides a viable system for producing cocoa beans of good quality attributes, comparable with using the traditional sun-drying, but without the associated drudgery.