Effects of bunch shading on the kinetics of maturation and polyphenolic components in grapes used to make sparkling wines in Franciacorta

In wine areas suitable for producing sparkling wines, the practice of bunch shading may represent a strategic vine management method inducing both a delay in the ripening of grapes and an improvement in the conservation of acidity. The effects of shading may also have implications for other grape components (i.e. polyphenolic composition) by changing the content of components such as cinnamic acids, flavonols and stilbene, sensitive to the exposure of grapes to sunlight. In this context, the practice of bunch shading was tested in Franciacorta in 2013, using shading nets on the Chardonnay and Pinot Noir cultivars. The experimental plan provided for a test without defoliation, another test with total defoliation and the application of various shading nets. Vegetative, productive and qualitative parameters were observed in vines and musts, while more specific analysis was carried out on grapes by applying an innovative method based on Ultraperformance liquid chromatography, which lasts 17 minutes and is performed on a Waters Acquity UPLC. The separation of the phenolic compounds was achieved on a Waters Acquity HSS T3 column 1.8 μm, 150 mm × 2.1 mm kept at 40 °C. Mobile phase A was water containing 0.1% formic acid; mobile phase B wasacetonitrile containing 0.1% formic acid. The flow was 0.4 mL/min. This targeted method has been developed for the quantification of 60 phenolics, such as benzoic acid derivatives, phenylpropanoids, coumarins, stilbenes, flavan-3-ols, flavonols, anthocyanins and thiols. Only in the case of cultivar ‘Chardonnay’ was the micrometeorological progress also monitored using four micrometeorological stations. From the data recorded it is possible to observe that total defoliation led to an advance in maturation of about four days as compared to the other treatments for both cultivars; in contrast, the shaded tests showed a delay in maturation and in the case of the Pinot noir cultivar, the best conservation of acidity. The ‘Chardonnay’ cultivar instead showed the best acidic conservation in the test without defoliation but shaded, while this parameter did not differ significantly in the case of the other treatments. As regards the data for different grape composition in terms of individual elements, it was possible to observe that defoliation carried out on Pinot noir without shading resulted in increased concentrations of cinnamic acids and flavonols, while in the same cultivar shading, and in particular the combination of lack of defoliation and shading, reduced this content as well as leading to a reduction in stilbenes. As regards Chardonnay, the same treatment instead showed a reduction in flavonols content, while in general, high levels of shading caused an increase in cinnamic acid concentration. The practice of shading seems to induce potential quality improvements in sparkling wine. Furthermore this particular type of vine canopy management leads to changes in the phenolic potential of grapes, with possible repercussions during vinification and pressing.