Stress relaxation in cherry fruit

Stress relaxation in three varieties of cherries was studied using the penetration test with a cylindrical pin, 4 mm in diameter, having a flat tip. One half of the fruit was modified by partial skinning, since experiments show that skin approximately doubles the apparent modulus of elasticity of the cherries. The skin also obscures a part of the fruit's distinctiveness, and affects the experimental results, even if a part of the fruit has been removed. A thermal activation theory with the residual part of stress was used to evaluate the stress relaxation experiments, and yielded results very similar to those previously obtained for vegetable flesh. Real consistency was observed mainly for residual stress and activation volume. It was observed that the relation between parameters Ct and log bt, and the initial relative slope of the relaxation curve provides information on fruit firmness.