A study of free normal impact between pairs of Granny Smith apples has been conducted. Bruising was generally more severe on one of the two fruit. Sometimes only one apple was damaged, and it was very rare for both fruit to be damaged equally. It is suggested that differences in the apparent ease of bruising of some varieties reported by growers may be more owing to variations of fruit physical yield strength around each fruit or between fruit in the same crop, than to absolute values of bruise susceptibility. It was found that the total bruise volume of the two fruit was linearly correlated with the energy absorbed. There was a non-linear relationship between the contact area and the impact energy, but the two were related by a 2/5 power law as predicted by elasticity theory. It was also found that the coefficient of restitution varied in a non-linear manner with impact energy, decreasing as the impact energy increased, to reach an asymptotic value of around 0·45. When the coefficient of restitution was above 0·7 very little damage was produced on the apples. © 1992 Silsoe Research Institute.
