FIRMNESS OF STRAWBERRIES AS MEASURED BY A PENETROMETER

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Abstract
An improved penetrometer designed for measuring the firmness of strawberry fruit is descr. The principle of operation is based upon the controlled uniform rate of application of the force necessary for fruit penetration by the plunger. The force is applied by the delivery of 30-mesh zinc metal from a funnel burette at a uniform rate to a container resting on the platform of a spring balance of 1000-gram capacity. The applied force is transmitted from the platform to the fruit plunger by means of a steel rod. A penetration depth of 5 mm. with a plunger 6 mm. in diam. proved satisfactory. Strawberries ripened in sunshine tended to be more firm than shade-ripened fruit. Larger berries appeared more firm than the smaller. Varietal differences in firmness are indicated and ranked in the following descending order: Blake-more, Massey, Missionary, and Klondike. Two new seedling vars. differed in firmness to the extent of 200%. Changes in firmness of Klondike and Fairmore strawberries during ripening are indicated. Wide variations in firmness occurred among fruits within samples and within individual fruits. These observations indicate the need of a refined sampling technique to increase the reliability of the firmness determinations for evaluating treatment differentials. The use of the penetrometer in evaluating changes in firmness under different storage conditions is indicated.

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