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

Renato L. Binati,Giovanna E. Felis,Maurizio Ugliano,Sandra Torriani,Eleonora Troiano,Ilaria Checchia

doi:10.3390/fermentation7010043

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.

Highlights

Chemical and microbiological composition of grape must play a central role in determining final wine characteristics; good sanitary conditions at harvest and before crushing are fundamental requirements for obtaining optimal results [1]
Washing treatment aims to remove the substances that accumulate on grape berry surface and can cause yeast stress during fermentation, such as chemicals, heavy metals, and spoilage microorganisms [7,8]
The experimental design considered a combination of three variables with two options for each: grape washing, SO2 addition, and starter inoculation

Summary

Introduction

Chemical and microbiological composition of grape must play a central role in determining final wine characteristics; good sanitary conditions at harvest and before crushing are fundamental requirements for obtaining optimal results [1]. In the Valpolicella area (north-east Italy), this traditional practice is applied in the production of renowned dry and sweet wines, such as Amarone and Recioto della Valpolicella, and consists of placing the harvested ripe and healthy grape bunches, mostly from the variety Vitis vinifera L.cv. After usually 2–3 months, the drying process causes concentration of sugars due to water evaporation Fermentation 2021, 7, 43 food use that usually is not washed before being processed [7]. Washing treatment aims to remove the substances that accumulate on grape berry surface and can cause yeast stress during fermentation, such as chemicals, heavy metals, and spoilage microorganisms [7,8]

Objectives

Methods

Results