In red grape varieties, anthocyanins and other polyphenols are located in berry skins, and their accumulation starts at veraison and continues during ripening. However, there are other compositional variables taken into account to determine the optimal maturity for harvest, such as berry acidity, often expressed as pH, titratable acidity and concentrations of tartaric and malic acids, berry weight, as well as the anthocyanin and total phenol concentrations (in red varieties). Grape berry ripening is usually described as the accumulation of sugars, and it is measured in terms of total soluble solids (☋rix). The vineyard variability maps generated for the different dates using this technology illustrate the capability to monitor the spatiotemporal dynamics and distribution of total soluble solids, anthocyanins and total polyphenols along grape ripening in a commercial vineyard. The best cross-validation and external validation (prediction) models yielded determination coefficients of cross-validation (R 2 cv) and prediction (R 2 P) of 0.92 and 0.95 for TSS, R 2 cv = 0.75, and R 2 p = 0.79 for anthocyanins, and R 2 cv = 0.42 and R 2 p = 0.43 for total polyphenols. Partial Least Squares (PLS) regression was used as the algorithm for training the grape composition parameters’ prediction models. Over the whole measuring season, a total of 144 experimental blocks were monitored, sampled and their fruit analyzed for total soluble solids (TSS), anthocyanin and total polyphenols concentrations using standard, wet chemistry reference methods.
Spectral measurements were acquired along four dates during grape ripening in 2017 on the east side of the canopy, which had been partially defoliated at cluster closure. On-the-go spectral measurements of grape clusters were acquired in the field using a VIS + SW − NIR spectrometer, operating in the 570–990 nm spectral range, from a motorized platform moving at 5 km/h. Visible-Short Wave Near Infrared (VIS + SW − NIR) spectroscopy is a real alternative to break down the next barrier in precision viticulture allowing a reliable monitoring of grape composition within the vineyard to facilitate the decision-making process dealing with grape quality sorting and harvest scheduling, for example.
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