Physical and thermal properties of coffee

The size, density, mass and crushing strength of arabica and robusta coffee berries were determined for underripe, ripe and overripe samples. The size, density and mass of the berries were the same and not influenced by the stage of ripeness. The crushing strength was higher for the underripe berries along the minor axis for both varieties. The robusta berries were harder than the arabica berries at all stages of ripeness. The size, crushing strength, porosity, bulk density, angle of repose, coefficient of friction, thermal conductivity, thermal diffusivity and specific heat were determined for the arabica and robusta parchments in the moisture range of 9.9-30.6% w.b. The size of the arabica and robusta parchments are independent of moisture content. The crushing strength increased along the length, breadth and thickness and decreased with increasing moisture content. The crushing strength was high across the thickness. The mass of 1000 parchments, porosity, bulk density, true density and angle of repose increased with moisture content for both arabica and robusta parchments. The coefficient of friction on various surfaces increased with moisture content. The mild steel surface offered the maximum friction followed by galvanized iron, aluminium and stainless steel. (C) 1999 Silsoe Research Institute.