Wine Composition and sensory science

Team leader: Dr Andrew C Clark (NWGIC)

Team members: Dr Celia Barril (NWGIC), Dr Nikos Kodoudakis (NWGIC), Prof Leigh Schmidtke (NWGIC), Dr Eric Wilkes (AWRI), Dr Marlize Bekker (AWRI)

The overall aim of this project was to develop knowledge regarding the Cu and Fe speciation in wine, wine binding agents and also to produce a routine test applicable for winery use that will allow winemakers to assess the impact of reactive metal in wine on spoilage and beneficial reactions.

Using a variety of techniques that measured different forms of metal ions in wine, a survey of 50 wines was conducted. The results showed that Cu is predominantly in a sulfide-bound form in wine, while the results for Fe were more variable and linked to organic acid- or phenolic-binders, depending on wine type. The sulfide-bound form of Cu was less reactive in catalysing oxidative reactions in wine, but could be converted to the more reactive non-sulfide bound form with oxygen exposure to wine or storage conditions conducive to loss of volatile compounds. Wines stored in anaerobic conditions, as found in most wines bottled under screw cap, tended to induce conversion of any non-sulfide bound forms of Cu in wine into sulfide bound forms. A colorimetric method for the measurement of Cu speciation in wine is currently being investigated.

The Determination of Total Cu in White Wine by BCA Colorimetric Analysis

Impacts of viticultural conditions and juice composition on the oxidative and reductive development of wine.

Team leader: Dr Andrew C Clark (NWGIC)

Team members: Dr Guillaume Antalick (University of Nova Gorica), Dr John Blakman (NWGIC), Dr Nikos Kodoudakis (NWGIC), Dr Katja Šuklje (University of Nova Gorica), Xinyi Zhang (NWGIC PhD Candidate)

The development of wine in bottle can often follow one of three pathways; ‘optimum’, oxidative or reductive, where ‘optimum’ is the wine balancing on a knife edge between reductive and oxidative. Recently the evolution of new analytical methodologies has provided great insight into the oxidative and reductive development potential of wine, including the ability to measure a reservoir of compounds able to influence wine development. More specifically, it is the free and bound volatile aldehyde compounds relevant to oxidative development (i.e., methional, phenylacetaldehyde), and free and bound sulfide compounds relevant to reductive development (i.e., hydrogen sulfide, methanethiol). Critically, a significant portion of these compounds are generated during fermentation and are present in the young wine, but hidden from the sensory features of the wine in bound forms. The release of the reservoir of bound forms of these compounds could significantly impact wine flavour even within the first year of bottling the wine.

This project project will assess production of the reservoir of potential spoilage compounds in the wine through a set of experimental Shiraz wines produced from warm/hot and cool/temperate vineyards under different water regimes from different vintages and sequential harvest dates.