Textural changes of coffee beans as affected by roasting conditions

During the roasting process, coffee beans change their textural properties, losing strength and toughness and becoming progressively more brittle, owi ng to chemical, physical and structural modifications. The aim of this paper is to evaluate the factors-such as density and moistu re-affecting the mechanical properties of coffee beans roasted at 170, 200 degreesC and under so-called high yield conditions. To distinguish the effe cts due to roasting (where both density and moisture changes occur) from th ose due to the water removal alone, heat treatments on coffee bean samples at dehydration temperatures (90-105 degreesC) have been also carried out. R esults 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 tiss ue structure owing to the pyrolysis phenomena and to the decrease of densit y. In fact, even if dried and roasted coffee beans showed, at similar moist ure 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.