Factors Affecting Soluble Solids, Acid, pH, and Color in Grapes

Abstract

Vines were grown from two-node cuttings and induced to retain one bunch of grapes per plant. These plants were grown in a greenhouse and parameters, such as leaf number and area, berry number, °Brix, acid, pH, and color, were recorded. Correlations between pairs of variables were made and analyzed. Plants with low berry numbers grew more than those with high numbers. Low berry number, high leaf growth rate, and high leaf/fruit ratio are related to high sugar levels, but acid levels were low and pH levels high. These levels were not simply a response to advanced maturity. While soluble solids levels increased only until a certain leaf/fruit ratio was attained, pH and acid continued to change as the shoots grew. Under the warm conditions of this experiment, unacceptably high pH levels and low acid levels were recorded. The effect of extended shoot growth increasing pH and lowering acid was not mediated by shade and leaf/bunch exposure since shading was not permitted. The general hypothesis that low vigor vines produce higher quality can, therefore, be explained in part by a direct response of pH and acid to shoot growth.