FIRMNESS TESTER FOR FRUITS AND VEGETABLES

A hand-held penetrometer has been developed to measure the compressive stress at a preset constant deformation. The principle is that the ratio of the compressive stress to the deformation is an appropriate characteristic of the elasticity and the firmness of the fruit.

The method is non-destructive if the compressive stress and the deformation are lower than the values belonging to the inflection point of the stress/ strain curve.

The penetrometer developed has the following main parts:

• handle,
• replaceable probe of 4, 6 or 8 mm diameter,
• frame to limit and to adjust the penetration of the probe to the desired value,
• force transducer,
• interface with an A/D converter in it,
• microcomputer to control the measurements and to measure, calculate and store results,
• link between the microcomputerand PC for data transfer.

The tester can be used to perform several measurements on a given fruit, calculate the coefficient of the elasticity, store the statistical characteristics. After several hundred measurements the result should be transferred into a PC and the tester and its microcomputer are ready to perform a new series of measurements.