Adressing vineyard variability by targeted berry sorting

Abstract

Variability of grape quality traits is encountered in vineyards between individual vines, between clusters within a single vine, and between berries of single bunches. While precision viticulture addresses systematic geologic and microclimatic variance within a vineyard, the within-vine and within-bunch variability are inaccessible to targeted management or selective harvesting. Recently, a new generation of berry sorting systems has emerged on the market, which allows single berry sorting by berry size, shape or reflection in several parts of the electromagnetic spectrum. However, the implications of berry size and optical properties for wine quality need to be understood in order to conduct targeted berry sorting. The aim of this project was to determine to which extent variability of berry quality traits exists on within-vineyard, within-vine and within-bunch level and to determine the covariance of berry optical properties with berry quality traits and finally to determine berry size and color effects on wine quality of Riesling (Vitis vinifera L.). Therefore, variance of grape quality parameters within vineyards, individual vines and bunches has been analyzed for sugar, organic acids, amino acids and skin phenolics (only within-bunch and within-vine variability) in the seasons 2010-2013. Results showed that within-vine and within-bunch variability exist on similar levels as within-vineyard variability. While organic acids, amino acids and phenolics correlated well with berry optical properties (VIS-Spectrum and Fluorescence) or berry size, others, especially sugars, showed little correlation. Results of a trial conducted in 2013 showed significant implications of berry size and color on the organic acid, terpenoid and norisoprenoid composition of wines obtained by micro-fermentation.