Influence of harvest time and withering length combination on reinforced Nebbiolo wines: phenolic composition, colour traits, and sensory profile

Abstract

Sforzato di Valtellina DOCG is a reinforced dry red wine produced in the mountain area of Valtellina alpine valley (North Italy), using ‘Nebbiolo’ grapes that undergo a withering process [1]. This process impacts on the grape composition due to a sugar concentration and changes in secondary metabolism influencing volatile organic compounds (VOCs) and polyphenols [2]. The ripeness degree of the grapes at the harvest time and the withering process length are key factors in modulating these changes. Therefore, the aim of this work was to evaluate the combined effects of these two variables on phenolic components, colour features, VOCs composition and sensory profile of wines produced with ‘Nebbiolo’ withered grapes. During three consecutive vintages (2019, 2020 and 2021), grapes were harvested from two vineyards, then three different binomials were tested: early harvest/long withering (EL), medium-term harvest/medium-term withering (MM) and late harvest/short withering (LS). The end of withering was set at 1st December of the harvest year for all conditions, and the grapes were subjected to winemaking in two independent replicates each. Basic wine parameters, total phenolic compounds (TPI), colour traits [3, 4] and VOCs were determined [5]. The results were supported by sensory analysis. LS samples, in both vineyards, had higher pH and lower acidity values compared to an earlier harvest. In addition, LS samples showed more stress compounds such as volatile acidity. In most cases, a reduction of TPI was observed in LS samples, specifically in 2019 for both vineyards. EL and MM wines displayed the darkest colour, with lower orange components compared to the LS. EL samples, in most years, showed highest content of terpenes, resulting in higher sensory perceived fruity and flower characters on average. LS samples presented a higher content of total benzenoids and lactones, that may have contributed to the lower liking of these samples, in which jam, hay, leather and caramel notes were perceived. Moreover, in some of LS sample a high concentration of N-(3-Methylbutyl)acetamide was detected, presumably influenced by a low grape health status [6]. A vintage effect was registered in mouth-feel sensations, in accordance with phenolic composition. In conclusion, EL and MM wines resulted in a higher phenolic content, with positive colour characters, and they were more appreciated by sensory analysis. Indeed, LS combination did not give advantages on final wine, particularly in total VOCs, and in some samples, it caused a decrease in health grape status.

References

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