Design and comparative evaluation of a three-layer coffee dryer

Abstract

Drying is an important processing step that prevents coffee from being attacked by bacteria and fungus that deteriorate quality. After coffee has been dried correctly, that is, dried to at least of 12 % wet basis moisture content; it can be stored safely with minimum risk of spoilage and quality deterioration. This study evaluated the drying performance of coffee beans dried in a newly developed three-layer coffee dryer, against rotary driers and traditional sun-drying. All the dryers were evaluated by measuring the uniformity of final moisture content and mechanical performance. The conclusion of this study is that, compared to sun-drying and mechanical rotary dryers, the new three-layer coffee drier yields virtually identical uniformity in final moisture content, yet it is achieved through a lower cost. This study also concluded that fuel oil is the most economical fuel to be used in the operation of mechanical dryers. Also, this study concludes that the sun-drying technique is the most expensive system to dry coffee in Kona for two reasons: (1) sun-drying coffee is inherently a manual-labor intensive process; and (2) the cost of manual labor in Kona is high. Lastly, this study's focus on sun dryers also shows that higher uniformity of final moisture can be attained by the incorporation of a three-times-per-day "Cenicafe" raking technique.