Fig. 6 displays the SSL graph which is somewhat sigmoid in appearance. SSL seems to increase parabolically from 21.9 N mm−1 to 40.8 N mm−1 during the first stage, continues to increase to 60.1 N mm−1 at the end of the second stage, and linearly increases to 68.7 N mm−1 at the end of the third stage. The shell is similar to wood whose mechanical behaviour is characterized by increasing strength with increasing age (Chou, 1998). Taiwania wood, for example, increases in density from 350 to 400 kg m−3, rupture stress from 0.233 to 0.252 N m−2 and modulus of elasticity from 54.94 to 58.37 N m−2 with an increase in age from 11 to 15 years. Determination of density (Mohsenin, 1996) of young coconut shell at the immature, mature, over-mature stage (five fruit for each maturity and three replications for each fruit) revealed that the shell density increased with maturity age (immature = 1087 kg m−3; mature = 1138 kg m−3; over-mature = 1174 kg m−3). As previously shown, the shell rupture force and the shell slope (which is a kind of firmness measurement apart from modulus of elasticity) also increased with maturity age. This agrees with the mechanical response of wood. The slope of the SSL curve reduces during the progression of the fruit from immaturity to over-maturity.