Correlations between Specific Gravity and Soluble Solids Concentration in Grape Berries

Abstract

We investigated correlations between specific gravity and soluble solids concentration in grape berries, since the nondestructive measurement of soluble solids concentration by near infrared spectroscopy is not put to practical use. Specific gravity of each cluster was measured by using an electronic balance and an acoustic volume meter that can measure volume without dipping fruits in water. Soluble solids concentration (Brix) of all berries in each cluster was measured using a refractometer. The relationship between specific gravity and Brix value of clusters of 'Kyoho' grape was constant and a linear one, regardless of the harvest year and the production district. The relation had a high correlation (r=0.981^***) within 16-23° Brix with a standard error of 0.35° Brix. High correlations were also found between specific gravity and Brix value in clusters of 'Campbell Early', 'Neo Muscat' and 'Koshu' grape. The slope of the regression line varied little among the four varieties. These results suggest that the measurement of specific gravity with an acoustic volume meter is a useful method to measure nondestructively the soluble solids concentration of clusters.