A New Instrument for Measuring the Compressibility of Tomatoes, and its Application to the Study of Factors Affecting Fruit Firmness

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Abstract
An instrument is described for measuring the compression of tomatoes under a known weight. This has been used to study the effect of some of the many factors likely to influence the firmness of tomatoes. The measurements of compression were made along the axis from the calyx to the stylar scar. The compressibility of the fruit increased threefold during ripening from the mature green to the fully red condition. The firmness of the fruits of two varieties increased with the number of locules per fruit. Comparison of the fruits of eight varieties showed marked differences in firmness; the even-ripening form of Potentate (Potella) was the firmest variety tested, and Harbinger the softest. The compression readings were significantly and negatively correlated with the percentage of walls and placentae, and with the thickness of the fruit as measured along the axis of compression. Fruit size and the percentage of walls were themselves positively correlated. Both lime and potash significantly increased the firmness of the fruit of variety Moneymaker. Phosphate had a slight beneficial effect, but no significant response was found to nitrogenous fertilizer. Tomatoes of two varieties, grown with different combinations of shading, day temperature and watering, were examined. Fruits grown at a day temperature of 85° F. (29-5° C.) were 30% softer than those grown at 65° F. (18-3° C.). Some evidence was obtained that heavy watering softened the fruit, particularly under hot, shaded conditions. Freshly-picked tomatoes of three varieties approaching the fully red condition continued to soften rapidly during storage (74° F.), the effect being highly significant even within three days. The effect of fruit size on the compression readings, and on percentage compression, is discussed.

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