Shade coffee in Hawai'i---quality, physiology, and biochemistry

Abstract

To explore the effects of shade level and type on coffee in Hawai'i, Coffea arabica L. was shaded with varying degrees of black and aluminized shade cloth, macadamia trees, and a novel, spray-on shade composed mostly of kaolin. These treatments were compared to unshaded coffee. Two locations were used in this experiment: Kunia, O'ahu and Kona, Hawai'i. The shading was imposed after the first major flowering of the season and maintained for 2 complete harvests. Measurements were made on yields, bean characteristics, specific leaf area, leaf temperature, leaf nutrient levels, nodal growth, organoleptic quality and photosynthetic response. Brewed coffee samples were analyzed using solid phase microextraction-gas chromatogtaphy to capture and analyze brewed coffee volatiles. These volatiles were used to predict organoleptic quality and group membership based on location, year of harvest and shade treatment. In addition, application of kaolin was explored using glass plates and slides to determine coverage and light transmittance. Shading resulted in statistically different yields in the macadamia (16% of sun) and kaolin (199% of sun) treatments in the second year, although a negative, linear trend was observed with increased shading. The lack of significant differences in yields between the cloth shaded and sun treatments was likely a result of1arge yield variation. Bean sizes were generally larger in shaded treatments and only the percentage of defects and broken beans were lower for the kaolin treatment in the second year in Kunia. Kona bean sizes were larger in the sun treatment but no differences were observed in bean characteristics. Kaolin treated plants responded similarly to sun plants for most measurements, although the responses tended to be more extreme when compared to the shade cloth and macadamia treatments. Kaolin treated leaves were 3.4°C cooler than sun leaves and photosynthesized 71 % more CO2 than sun plants. Shading did not appreciably affect organoleptic quality. Furthermore, brewed coffee volatiles were not good predictors of organoleptic quality. However, with few to no misclassifications, the volatiles could accurately predict group membership.