During the roasting process, coffee beans change their textural properties, losing strength and toughness and becoming progressively more brittle, owing to chemical, physical and structural modifications. The aim of this paper is to evaluate the factors-such as density and moisture-affecting the mechanical properties of coffee beans roasted at 170, 200 degreesC and under so-called high yield conditions. To distinguish the effects due to roasting (where both density and moisture changes occur) from those due to the water removal alone, heat treatments on coffee bean samples at dehydration temperatures (90-105 degreesC) have been also carried out. Results showed that the typical brittleness of roasted and high yield coffee beans seems to be related both to the water loss and to the change of tissue structure owing to the pyrolysis phenomena and to the decrease of density. In fact, even if dried and roasted coffee beans showed, at similar moisture content, a reduced and weak significant difference in the resistance to fracture and in roughness, roasting caused a decrease of the deformability, the index of a brittle and fragile texture.
