An Accurate, Low Cost Firmness Measuring Instrument*

Abstract

A low-cost, automatic firmness measuring instrument was developed using commercially available components such as: dial gage, dashpot lowering mechanism, weight sets and probe tips. The details of the assembly and the names of parts manufacturers are given. The instrument is an automated modification of the original P-L Meter developed by Parker and Levin at Michigan State University. The application of the instrument to firmness measurements on cherries and tomatoes is summarized and illustrated with typical results. Tomato studies covered the relationship between firmness and variables such as: fruit size, cultivar type, changes in protopectin content, polygalactu-ronase and cellulase activity. The readings compared favorably with those obtained with the Instron Universal Testing machine.

Evaluation of Two Objective Methods and a Subjective Rating Scale for Measuring Tomato Fruit Firmness1

“…The acid concn delcines until Nov. and remains more or less constant thereafter (2,3). A similar pattern was described for grapefruit in California (19), Texas (5), and in certain years in Florida (7). Concn of titratable acidity in juice may be stable, but the absolute amount of acid calculated on a per fruit basis actually increases due to fruit growth and accumulation of acid during this time.…”

“…The fruit is less palatable when this happens than it was in Nov. There are reports which indicate that acid levels in citrus fruit is related to environmental conditions (4,5,13,15,16,19,20). Rasmussen et al (15), for example, reported a correlation be tween high temp and acid content of young orange fruit, and an inverse relationship between mean acid content of 'Ruby Red' grapefruit and rainfall.…”

“…Instruments for nondestructive determina tion of tomato fruit firmness have been based on measuring resistance to compression force applied at a single or multipoints on the fruit. They include the Cornell Pressure Tester (10), Firm-o-meter (13), Asco Firmness Meter (8), Pressure-Load meter (5,17), penetrometer (3,4), and other deformation testers (15,18). Gromley and Keppel ( 9) used a modified shear press to measure tomato firmness by compressing the fruit by 5 mm between two flat surfaces.…”

A method for measuring tomato fruit firmness using a modified shear press

“…Other firmness meters for tomatoes, the Firm-a-meter and the Ansco meter were described by Garrett et al (1960). Diener, Sobotka & Watada (1971) measured tomato fruit firmness with a modification of the original . P-L meter.…”