Stream 1.1: Defining and controlling important volatile compounds in wine and their impact on wine aroma and flavour

Knowledge of the critical chemical compounds that are responsible for the sensory characteristics of wines is of great importance to be able to control and adjust wine flavour during wine production. Compounds not previously recognised as contributing to flavour have been identified for the first time through work in this stream, including the compound rotundone: giving Shiraz wines from many of Australia’s wine regions their distinctive peppery or spicy flavour. In addition, numerous compounds not previously understood adequately have been revealed as significant, and ways of adjusting their contribution have been examined. For example, the Eucalyptus/mint compound eucalyptol was found as a consequence of nearby eucalypt trees, with aerial transfer an important element, but much less influential than the presence of grape-vine or eucalypt leaves in the harvested grapes. Studies into the origin, formation and chemical stability of many compounds have provided guidance for wine producers to dial up or down these compounds. For example, this research included the determination of the ‘tropical fruit’ thiols precursors, which allowed the recognition that post-harvest storage of crushed grapes gives greatly enhanced levels of these compounds. Further major outcomes of the activities under this stream have been the development of analytical tools for measurement of key wine flavour compounds, and knowledge of viticultural and winemaking options that alter the levels of these flavours. Another major aspect of the work concentrated on off-flavours. Winemakers now have improved ability to avoid unpleasant and economically damaging taints and ensure wine is suitable for sale. The work on off-flavours included compounds responsible for ’reductive’ offflavour, found to be largely due to hydrogen sulfide and methane thiol, and smoke taint originating from bushfires. For smoke taint, grape metabolites have been identified as precursor compounds that release the taint inmouth during consumption.