Measuring blueberry firmness and modelling quality changes for delays in cooling using the FirmTech II

A FirmTech II instrument was evaluated to determine the effects of instrument settings, berry orientation and berry size on firmness values of blueberries. Blueberry firmness values (g/mm) measured by a FirmTech II depended on calyx orientation (up, down, or horizontal). In addition, large changes in firmness readings resulted from different minimum and maximum instrument settings. We propose a recommended standard is to use only the first measurement, with the calyx horizontal, at 50-g minimum and 150-g maximum force. Applications of Hertz contact equations (ASAE standard S368.4) showed a need for including the radius of the fruit and the 3/2th power on the deformation value in the FirmTech II output.

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