Variation of the physical and aerodynamic properties of coffee cherries during drying: Determination and modeling

Abstract

The reduction of moisture content in coffee cherries, during drying, directly influences their physical and aerodynamic properties and quality. The knowledge of these properties is essential for cost reduction, correct conservation, and defining parameters and operation of equipment in the main postharvest operations of the crop. In this study, the main physical properties (unit specific mass, sphericity, circularity, geometric diameter, projected area, volume, and volumetric contraction) and aerodynamic properties (terminal velocity and drag coefficient, actual, and theoretical) were determined during the coffee cherries drying. The reduction of the moisture content during drying provides a reduction of 30% in the specific density of coffee cherries. In addition, it promotes the reduction of sphericity, circularity, projected area, geometric diameter, and volume of the fruits. A volumetric reduction of 40% during the drying process was observed. A new model was proposed to represent the volumetric contraction of coffee cherries during drying. The experimental terminal velocity of coffee cherries decreased during the drying process, while the drag coefficient showed an increasing trend. The theoretical aerodynamic properties found in this study, presented values close to the experimental ones, representing satisfactorily the phenomena in the function of the moisture content.