Drying gayo coffee under natural processing by using modified Hohenheim solar tunnel dryer in Gayo highland

Gayo highland has relatively low daily temperature which is not effective for drying coffee. The objective of this study was to examine the operation of modified type Hohenheim solar tunnel dryer with 33% absorber area for drying coffee under natural processing in Gayo highland. About 9kg coffee cherries were dried by using the dryer and about 1 kg was dried under sun drying method. Results showed that the drying temperature of modified type Hohenheim solar tunnel dryer was higher about 9 to 14°C than the temperature of sun drying method. However, the relative humidity was about 40% both inside the drying chamber and outside the dryer. In order to reach the moisture below 14%, the drying time of coffee cherries by using the Hohenheim solar tunnel dryer may take for 8—9 days (64—72h) whereas the drying time by using sun drying method needs about 40 days (320h). It was found that the drying rate of coffee cherries dried by using Hohenheim solar tunnel dryer was higher than that of dried by sun drying method. In conclusion, the modified type Hohenheim solar tunnel dryer is promising to be used by farmers in Gayo highland.