Vineyard management strategies adopted to mitigate the impacts of climate change affect the evolution of phenolics and color during bottle aging of Aglianico wines

Abstract

In recent years several strategies have been proposed to cope with the effect of climate change on grape berry quality but only a few studies have dealt with the influence of management practices implemented in the field (e.g. irrigation,summer pruning, etc.), on the evolution of wines over time. 
Three irrigation treatments (I0,I50,I100) and three shoot trimming treatments (T0,T30,T75) were applied to Aglianico grapevines for two consecutive years(2017 and 2018), thus resulting in nine experimental samples, namely T0I0, T0I50, T0I100, T30I0, T30I50, T30I100, T75I0, T75I50, T75I100. The grapes were harvested and vinified separately, the vinifications were standardized and, after stabilization, the wines obtained were bottled and aged in controlled conditions. Apart from base parameters of grapes and wines, the phenolic composition of hydroalcoholic extracts derived from skins, grape seeds and wines were determined just after the end of vinification and after a long bottle aging (4 and 5 years). Likewise, the chromatic characteristics of wines were analysed as well.
Berry soluble solid content and alcohol concentration in wines turned out to be reduced by shoot trimming and deficit irrigationin eitherseason. However, these effects were enhanced in the first year of treatment. Severe shoot trimming treatment induced a significant decrease in the amount of tannins extractable from skin and seeds that reached a reduction of 83% in grapes under severe water deficit and severe shoot trimming in 2017. Both treatments determined a decrease in anthocyanins extractable from grape skins (never above 17%) determining a significant effect also on color intensity and hue in the wines of both the 2017 and 2018 vintages. The vintage drastically influenced the amount of flavanols and tannins but the effect of the trimming treatment was comparable. Although the great production of polymeric pigments over time in all wines, the effect detected on grapes and wines just after fermentation is still evident for color intensity,tannins and vanillin index after bottle aging.
The results obtained in this work showed that, apart from the expected effect on soluble solids of grapes and alcohol content of wines, a strong effect of shoot trimming on tannins and vanillin index was detected. If further confirmed by other experiments, the trimming could be an interesting practice for the production of wines with lower amounts of tannins and, likely, less astringent.