Coefficient of Friction, Angle of Repose, Specific Gravity, and Bulk Density of Coffee Fruits and Coffee Beans

Abstract

The coefficients of friction between coffee fruit, coffee beans, and different construction materials were determined by the tilting-table method. Determinations were performed for dry-surface and wet-surface fruit, pulp, pulped unwashed-wet, and pulped washed-dry beans. The pulped, washed, wet beans showed the highest coefficient of friction when compared with fruits, pulp, pulped-unwashed or pulped-washed dry beans for all materials of construction. Values obtained ranged from 0.65 for stainless steel to 1.15 for planed wood (across grain). The dry beans, 12-percent moisture content, dry basis, showed the lowest coefficient of friction when compared with fruits, pulp, pulped-unwashed or pulped-washed wet beans. The values obtained varied from 0.34 for stainless steel to 0.55 for concrete. These values are similar to those obtained for rough rice by Kramer (5) on the same materials. The specific gravity for green fruit varied from 1.0063 to 1.1163 and for the ripe fruit from 1.0072 to 1.0884. The values obtained for specific gravity, bulk density, and void space for coffee are similar to the values published by Zink (9) for wheat, oats, buckwheat, and millet.