A penetrometer is very useful for evaluating fruit firmness, but no systematic study yet exists on the physical significance attributed to the curve variations. A tissue model, based on computer graphic methods, allows the simulation of penetrometric tests on apples. There are varying physical factors such as intercellular space, cell arrangement, cell stiffness and tissue cohesion. The real forward limit of the plunger may take, and curve fluctuations are due to the periodic evacuation of those cells. The most influential factor in a penetrometric measurement is individual cell stiffness, its variation with depth can be evaluated with the curve mean slope
