The effect of air flow rate on single-layer drying characteristics of Arabica coffee

This study was intended to evaluate the behavior of Arabica Coffee (Coffea arabica L.) bean during the single-layer drying process under several levels of drying air velocity. The research was carried out at the Processing Laboratory of Agricultural Engineering Department, Hasanuddin University - Indonesia, during the period of February to May 2011. Sample used was an Arabica Coffee, Line S-795 variety, obtained from a coffee farmer in Enrekang Regency - South Sulawesi. The main equipment applied was a tray dryer, Model EH-TD-300 Eunha Fluid Science. The dryer was constructed to flow the drying-air parallel with the crop-layer. Three different levels of air velocity (0.5, 1.2, and 1.8 m/s) under constant drying temperature of 47°C were exercised in this research. The moisture ratio was determined for each drying run and fitted to several existing thin-layer drying models. Research results indicated that among the models, Hii et al. model (2008) is the best one, R² reached up to 0.99, to represent the behavior of the Arabica Coffee during the single-layer drying process. It was also observed that increasing air velocity from 0.5 m/s to 1.8 m/s failed to considerably improve the drying rate, although the paired t-test indicated that their moisture ratios were statistically different. The curves of the moisture contents (dry-basis) resulting from the three levels of air velocity across elapsed drying time were very much overlapping, especially at the elapsed drying time greater than 10 hours.