Comparison of four new devices for measuring kiwifruit firmness

Four new methods of measuring kiwifruit (Actinidia deliciosa) firmness which have been developed in New Zealand have been compared and evaluated. They are: (1) ''SoftSense'', developed by HortResearch, Ruakura, using characteristics of a fruit's bounce to calculate ''dwell time'' which varies with fruit firmness; (2) ''Softness Meter'', developed by Massey University, Palmerston North, using the rate at which the fruit surface is deformed by a known load; (3) ''KIWIPOKE'', a hand-held wand, developed by Industrial Research Limited, Auckland, using characteristics of a small ballistic collision against the fruit to give a firmness value calibrated to equate to a penetrometer reading; and (4) ''Massey Twist Tester'', a destructive test, developed by Massey University, Palmerston North, measuring the force required to rotate a small plate within the fruit flesh. Using prototypes of the three non-destructive devices, we repeatedly tested the same fruit as they softened during coolstorage. Additional fruit were used to compare fruit firmness measured by the four new devices with results obtained using a standard Effegi penetrometer. The ability of the devices to differentiate between different lines of fruit, and the ease of operation are discussed. Although it is clear that a non-destructive method to measure fruit firmness will have considerable advantages, at present none of the devices tested can be recommended unreservedly for general use. However, all these devices are undergoing further development as a consequence of this and other evaluations.