Factors affecting Arabica coffee bean size in Kenya

Abstract

SummaryThe proportion of large, commercially valuable coifee beans (6.75 mm sieve) varies greatly within and between years in Kenya and is altered by field treatments which affect the water status, seasonal fruiting pattern and yield of the trees.Defoliation trials suggested that little of this variation could be attributed to changes in assimilate supply during fruit development, although these could explain differences in the weight of the fruit pericarps. The largest differences in bean size recorded in past field trials at Ruiru were associated with differences in rainfall, and presumably tree water status, while the fruits expanded; the ovules did not reach full size when they expanded during dry weather.These conclusions are discussed in relation to the selective pressures that may operate in coffee’s native forest understorey environment, and its tendency to ‘overbear’ in unshaded plantations.