Biophysical control of coffee quality : the case of southwestern Ethiopia

The specialty coffee market is constantly growing mainly due to an increased interest in taste and other quality attributes of high quality coffee. This growing demand for high quality coffee triggered coffee producing countries to produce specialty coffees for the top-end markets. In Ethiopia, using 'total specialty cup scores', top quality coffees are grouped into Q1 (specialty 1, score: ≥85) and Q2 (specialty 2, score: 80 - < 85). This classification resulted in market segmentation and higher prices on the international markets. Coffee quality is, however, determined by numerous factors along its value chain. Growing environment, harvest period, cherry sorting, postharvest processing methods and types of actors involved in the supply chain are known to predominantly affect coffee quality. This study investigated influences of these factors and their interactions on coffee quality. This PhD research indicated that coffee beans from high altitude with open or medium shade and early to middle harvest periods gave superior bean quality. At high altitude, however, dense shade decreased the share of Q1 coffee by 50%. At high altitude, early harvesting led to 73% Q1 beans compared to only 27% for late harvest. Regardless of harvest period, at mid (or low) altitude, coffee samples gave >80% is Q2 coffee. Further, this PhD also revealed that dry processing positively influences coffee quality and allows enhancing preliminary total quality, overall cup preference and aroma attributes. In addition, because of easy management, low production cost and sustainability, dry processing should be recommended over washing methods. Finally, a NIRS model predicting coffee cup quality from green bean NIR spectra was also successfully developed. The model is a promising tool for fast and accurate assessment (i.e. Q1 vs. Q2) of specialty coffee quality. All together this PhD identified important biophysical factors that control coffee bean quality along the coffee value chain, which opens introduction of concepts and methodologies enhancing coffee quality.

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