Unravelling the Impact of Grape Washing, SO₂, and Multi-Starter Inoculation in Lab-Scale Vinification Trials of Withered Black Grapes

Abstract

Wine quality is strongly affected by chemical composition and microbial population of grape must, which, in turn, are influenced by several post-harvest treatments, including grape withering. Different strategies have been suggested to manage the fermenting must microbiota, as it plays a central role in the outcomes of both spontaneous and guided fermentations. This study aimed at evaluating the impact of grape washing, SO2 addition, and selected starter culture inoculation on population dynamics, fermentation kinetics, and main oenological parameters in lab-scale trials, focusing on withered grapes usually used for Amarone production. Although grape washing treatment was effective in removing heavy metals and undesirable microorganisms from grape berry surface, inoculation of multi-starter cultures impacted more fermentation rates. Further, both grape washing and starter inoculation procedures had a remarkable impact on wine chemical characteristics, while 30 mg/L SO2 addition did not significantly affect the fermentation process. In summary, the best strategy in terms of limiting off-flavors and potentially reducing the need for SO2 addition in wine from withered grapes was the use of yeast starters, particularly mixed cultures composed by selected strains of Metschnikowia spp. and Saccharomyces cerevisiae. Application of a washing step before winemaking showed a potential to improve organoleptic characteristics of wine.

Keywords

• withered grapes
• grape washing
• heavy metals
• grape microbiota
• mixed starter cultures
• fermentations