Measurement of Tomato Firmness With a Universal Testing Machine

A technique of punch-testing tomatoes to measure the firmness of the different anatomical parts has been developed. A plunger with a 0.040 inch diameter tip tapering to a 0.020 inch diameter shaft is attached to the crosshead of an Instron Universal Testing Machine and driven into the tomato at a speed of 1 cm/min. Distinct peaks are observed on the force-displacement trace which are related to the firmness of the various parts of the structure. The method can be used to follow changes in firmness during ripening, to detect ripening abnormalities, to measure differences between varieties and to detect variations in firmness over the surface of individual tomatoes.