The relationship between elevation, soil temperatures, soil chemical characteristics, and green coffee bean quality and biochemistry in southwest Ethiopia

Green coffee bean quality and biochemistry are influenced by environmental variables. The present study was designed to study the influence of soil temperatures and soil chemistry on bean physical attributes, bean quality (assessed by three internationally trained, experienced, and certified Q-grade cuppers licensed by the Specialty Coffee Association (SCA) Coffee Quality Institute (CQI) and biochemistry of green coffee beans). The study was performed in 53 farms in southwest Ethiopia distributed along an elevational gradients (1500-2160 m a.s.l.) and with varying shade canopy cover (open to dense shade). A total of 159 individual coffee trees were sampled. Shade tree canopy cover, soil temperature, and soil chemistry, as well as coffee management intensity, were quantified as explanatory variables. Green bean quality was negatively correlated to soil temperatures. On the other hand, hundred bean mass and green bean biochemistry (caffeine, trigonelline, and chlorogenic acid contents) were negatively correlated to soil temperatures but positively to soil chemistry. During the coffee fruit development period (flowering to fruit maturity), temperature appeared to be a driving factor influencing coffee bean quality and biochemistry. Total specialty quality was significantly associated with soil chemistry, in which 84% of the variation could be explained by soil chemical variables. This study is the first to demonstrate the relationship between soil temperatures and chemistry in coffee bean quality and green bean biochemical compositions. Although the relative importance of factors such as air temperatures and humidity and soil moisture are missing from this study, we find that soil temperatures and soil chemistry have a strong effect on coffee bean quality and biochemistry. Overall, climate change, which generally involves a substantial increase in mean temperatures of tropical regions, could be expected to have a negative impact on coffee bean quality and biochemistry