This photo was taken in Guji, Ethiopia by green buyer Toby Harrison. It shows ‘garden coffee’ growing in partial shade in amongst a crop of ensete which has an edible heart and is made into cereals and certain staple foods in the Ethiopian diet.
It is clear that shade coverage is able to reduce average temperatures for coffee plants. An experiment by Vaast et al. (2005) using 45 percent shade netting in Costa Rica found a significant difference between inner and outer leaf temperatures of coffee plants and a significant overall temperature drop. They measured differences of 4◦ C for inner leaves (measure from the trunk up to the sixth leaf) and 2◦ C for outer leaves. The same experiment accumulated sensory impressions of coffee grown under differing levels of shade cover. The chart below records the findings of their sensory panel. In addition, to testing full sun and shade, they also tested fruit load by removing a quarter and a half of the fruit from certain trees. The reason for this is that full sun plants tend to overbear and so the experiment sought to test if pruning could counteract this issue whilst still yielding good tasting coffee under full sun. The panel showed a clear preference for the shade-grown coffee over two growing seasons.
This chart records sensory impressions from the panel assessing the Costa Rican fruit thinning and shade experiment Vaast et al. (2005)
A scientific study conducted on Reunion Island (the site of the Typica variety’s famous mutation into the Bourbon variety) collected sensory and chemical data from sixteen microclimates across the island. This research found a correlation between a cooler climate and positive sensory performance.
‘Positive quality attributes such as acidity, fruity character and flavour quality were correlated and typical of coffees produced at cool climates.’
One theory to explain why coffee may taste better in shade is the slower maturation of the fruit.