*3.2.2 Mechanical driers*

During the mechanical drying, the beans are heated by hot air that passes through the machine and dries the coffee. Also, it carries away the moistures from the drying coffee. Controlling the drying temperature is the most critical part, and it should not exceed 45°C for whole cherries and 40°C for parchment coffee. Commonly there are two kinds of mechanical drier, such as static and revolving driers. Revolving driers include column driers, vertical driers, rotary driers, cascade driers, and flex driers, and there are tray driers with a stirrer [50]. All these driers can work with fuel oils, gasses, woods, and other energy sources. A report indicated that the best quality coffee was gained when the drying processes were done at two stages, an initial period the drying was performed at low temperature (20°C) and the second stage followed by higher temperature (60°C) [51].
