Tempo di raccolta ed effetti di disidratazione post-raccolta sulla composizione fenolica finale delle uve Nebbiolo destinate alla produzione di vino DOCG Sforzato di Valtellina

Nebbiolo is an Italian black wine grape variety from Piemonte, and the derived wines are characterized by low color intensity, richness in tannins, and good aptitude for long aging. In Valtellina region (Lombardia), a special dry wine, the Sforzato di Valtellina, is produced by postharvest dehydration of Nebbiolo grapes. In this study, the grapes were collected at three different harvest dates based on the sugar accumulation from two vineyards in the Sforzato di Valellina DOCG area, Villa di Tirano and Berbenno. The grapes were subjected to a postharvest dehydration process in typical fruttaio, (uncontrolled conditions - temperature, relative humidity) with the aim to understand when is the best harvest point where the grape phenolic composition, as a total and extractable fraction in berry skins and seeds, is enhanced in fresh and partially dehydrated berries. Chemical traits of grapes were then evaluated through spectrophotometric and HPLC methods. The variations in the phenolic extractable content in dehydrated grapes were found to be different between the vineyard areas in berry seeds and skins. Generally, the extractable content increased after the dehydration process and decrease as the harvest time progresses. Total phenolics in dehydrated grapes showed a decreasing trend when advancing the harvest date, whereas seeds response was different among the studied vineyards. Mostly, an increasing trend was found in total phenolic after the dehydration process. Few significant differences were found in the anthocyanin profile of dehydrated grapes, although a relative decrease was showed in some monoglucoside anthocyanins that are more susceptible to oxidation, leading to a percentage increase of more stable forms.