Non‐destructive measurement of kiwifruit firmness

Design and operation of two prototypes of an instrument for measurement of fruit softness and its application to characterisation of kiwifruit (Actinidia deliciosa) softening behaviour are described. The “softness meter” was used to measure deformation of the fruit surface beneath a small spherical probe under constant load with time and caused negligible damage to the tested fruit. Softness was quantified as a “softness coefficient”, estimated as the slope of the regression line of deformation on the natural logarithm of time. After an initial delay in softening, softness coefficients of kiwifruit increased approximately linearly with time in storage at 0°C and were inversely and hyperbolically related to penetrometer data obtained on the same fruit. Repeated measurements on individual fruit, made possible by the non‐destructive nature of the softness meter, will enhance control of experimental error in research on fruit softening behaviour.