The Development of Coffee Bean Drying Process Technology – A Review

Abstract

Coffee is an important export commodity for Indonesia. Coffee drying is post-harvest processing that greatly determines the coffee quality and microbiological safety. Conventional/sun drying is time-consuming, depending on the weather, and can potentially contaminate coffee beans by dust and moisture readsorption under high relative humidity. These problems could be avoided by employing artificial drying. This literature review aims to identify the current status of coffee drying technology, its advantages and limitations, to obtain coffee beans with the desired quality, duration of drying time, and energy consumption for processing. From the three types of thermal radiation dryers being reviewed, namely tray dryer, rotary dryer, and fluidized bed dryer, it was concluded that the drying air temperature and relative humidity must be selected properly to obtain the microbiological safety and the quality of the coffee brew. Efficient energy consumption requires a balance between the rate of water evaporation inside the coffee grain and the rate of water vapor removal from the solid surface by the air stream. The most efficient coffee drying is achieved at an air temperature of 50 o C, resulting in drying time and energy consumption of 65%, and 50% lower than that of 40 o C, with a good quality of the coffee brew. Fluidized bed drying combined with zeolite adsorption is potential to reduce the drying time due to an enhancement of air capacity to absorb water vapor. Application of microwave for coffee drying resulting in much shorter drying time than conventional thermal drying, but has a drawback of un-uniform grain temperature. A hybrid drying system could be implemented by using microwave and thermal oven.