Effect of sun drying methods and layer thickness on quality of selected unwashed Arabica coffee varieties in jimma zone

Abstract

Coffee is the most important crop in the national economy of Ethiopia and continues to be still the leading export commodity. Despite the economic importance, productivity and quality of the crop is very low, primarily because of poor field management and post harvest handling practices. Improper post harvest processing techniques largely contribute to the decline in coffee quality and are influenced by several factors, of which post-harvest on-farm processing is the major one. Though Jimma is well known as the center of coffee diversity and high production potential area in Ethiopia, the quality of its coffee does not have deliverable grade status and seeks further improvement. This calls for intensive efforts to identify post-harvest practices and drying techniques and to come up with technical recommendations that enhance coffee quality. Therefore, this experiment was carried out to determine the effects of altitude, sun drying methods, variety and cherry drying layer thickness on quality of coffee under different location of Jimma zone. Accordingly, on-farm processing experiments were conducted in Jimma zone at state owned coffee farms under Limmu Coffee Plantation Development Enterprise (LCPDE) from September up to December, 2010. The experiment was laid out in 3x3x3x4 Split-Split-Splitplot design arranged in CRD with three replications. The four factors comprise three locations: Gomma-1, Gomma-2 and Kossa coffee farm sites assigned to the main plots; three drying materials: bricks floor, raised beds with bamboo mats and raised beds with mesh wires assigned to the sub-plots. Three coffee varieties: 744, 74110 and 744+74110 assigned to sub- sub-plots and four levels of cherry layer thicknesses: 20; 30; 40kg/m2 (uniformly spread) and the farmers’ conventional practices (40kg/m2 ) as sub- sub-sub plot treatments. The treatment combinations comprised 108 units replicated at each location, providing a total number of 324 sample sizes. Combined analysis was applied after homogeneity test to estimate the average response suitable for particular location. Similarly, cupping was done by three cuppers at (OCFCU) coffee cupping laboratory in March, 2011. The data were computed by using list significant differences (LSD) procedures of SAS version 9.2. As a result, the interaction effects were highly significant (P≤0.01) for hundred bean weight and total coffee quality and significant variations were observed (P≤0.05) for drying period, total raw quality, total cup quality and coffee grades. The finding revealed that; depending on the agro-ecologies, processing coffee on raised beds using appropriate layer thickness loads of 20 to 30kg/m2 and 40kg/m 2 at low/mid and at high Keywords: Effect, sun-drying, layer thickness, on-farm processing, total quality and specialty coffee altitudes produce quality coffee identified as total quality scores ranging 80-89.99 points and can attain “Specialty Grade 1 and 2” classification profiled under grade 2.While, the conventional systems produce low quality coffee identified as commercial grade classifications profiled under grade 3 to 6. Hence, using appropriate dry processing approaches, it is possible to produce specialty coffee at different agro-ecologies. However, further study including stirring frequency, identification of the actual differences in quality on distinctively processed coffee and action research to improve the processing practices should be conducted to give concrete recommendations.