Grape Heterogeneity Index: Assessment of Overall Grape Heterogeneity Using an Aggregation of Multiple Indicators

Area of Science:

• Viticulture and Oenology
• Agricultural Science
• Plant Physiology

Background:

• Uniform grape maturity is crucial for optimizing wine quality by minimizing underripe or overripe fruit.
• Grape heterogeneity is a complex issue impacting vineyard management and harvest timing decisions.
• Existing methods lack a comprehensive metric to quantify overall grape variability.

Purpose of the Study:

• To develop a composite index for quantifying grape heterogeneity.
• To assess the impact of viticultural practices on grape heterogeneity.
• To aid vineyard managers in making informed decisions regarding harvest dates.

Main Methods:

• A grape heterogeneity index (GHI) was created by aggregating residuals and ranges of key grape parameters (TSS, pH, weight, tannins, color, pyrazine, malic acid).
• Cabernet Sauvignon grapes were analyzed under varied crop loads and irrigation regimes over two growing seasons (2019/2020, 2020/2021).
• GHI scores were compared across different ripening stages and in relation to viticultural factors like yield, leaf area, and pruning weight.

Main Results:

• Grape heterogeneity, measured by GHI, generally decreased during ripening but significantly increased near harvest in 2020, while plateauing in 2021.
• Neither irrigation nor crop load significantly affected grape heterogeneity at harvest across both vintages.
• Early in ripening, higher vine yield, leaf area index, and pruning weight correlated with increased GHI, but this relationship diminished by harvest.

Conclusions:

• The developed GHI provides a valuable tool for assessing and managing grape variability in vineyards.
• Viticultural practices like irrigation and crop load did not significantly influence grape heterogeneity at harvest.
• Early-season vine vigor indicators (yield, LAI, pruning weight) impact heterogeneity, highlighting the need for timely management strategies.