Winemaking interventions to modulate glutathione status: effects on white wine quality
Summary
Objective
To determine the usefulness of glutathione additions and whether or not there are ‘off target’ effects related to its use. A risk reward matrix will be developed to help guide the use of glutathione in an environment where the regulated use of this additive may change and where practitioners may seek to augment or replace sulphur dioxide (SO2) as a protectant against oxidation.
Background
Although SO2 is the antioxidant most commonly used to preserve wine quality, less aggressive alternatives are continuously being sought. Reduced glutathione is a naturally occurring antioxidant from grape and yeast that may provide a solution. While glutathione may contribute to the production of quality wine, its effect on the expression of terroir and varietal character is not well defined. Much of the work associated with glutathione manipulation has targeted Sauvignon Blanc, aiming to preserve varietal thiols and colour in bottled wine. Thiols also contribute to the character of other varieties; however, the impact of glutathione addition on wine quality is relatively unknown. This project aims to extend our understanding of the effects of glutathione addition in juices and wines in other varieties as well as Sauvignon Blanc.
Research approach
The project will use juice from a number of white varieties, principally Chardonnay, Riesling and Sauvignon Blanc. Inter-vintage experimental work will make use of stored juice to obtain oxidatively stable juice. This will be used to understand biological uptake and utilisation of added glutathione. Protective juice treatments, direct glutathione addition and microbial consumption of glutathione will be considered. The fate of added glutathione will be determined through use of isotopically labelled compounds (containing 34S), which will aid in determining the degree to which glutathione turnover contributes to late-ferment hydrogen sulphide production. Small-scale winemaking trials will be used to assess the sensory and chemical impact of glutathione treatments. This work will elucidate how glutathione in combination with other factors can be used during grape processing to manipulate or preserve grape typicity, regional characters and wine quality.
Sector benefits
The outcomes of the work will inform decisions on the applicability and usefulness of glutathione as an alternative antioxidant to SO2.
This work may also help to support a niche but premium market segment that seeks to decrease SO2 use in winemaking, as well as delivering strategies to make wines that are more suited to those with sensitivity to sulphite.