To characterise the formation and fate of volatile sulfur compounds, and the biochemical pathways in grapes and yeast that affect their formation. A multidisciplinary approach will be used to understand the accumulation volatile sulfur compounds from fermentation through to bottle-aged wine.
The level of volatile sulfur compounds in wine is influenced by factors including yeast selection and fermentation conditions; the nature and quantity of precursor compounds; the availability or absence of oxygen at different points of the winemaking process; and the availability and speciation of transition metal ions such as copper. As a defence against the formation of undesirable volatile sulfur compounds, especially hydrogen sulphide, winemakers typically rely on monitoring must nitrogen levels, additions of diammonium phosphate and copper, and choice of closure and its oxygen transfer rate. However, despite these commonly used practices, release of volatile sulfur compounds post-bottling and sulfur-related off-flavours can still occur.
The project will evaluate the main precursors to sensorially important volatile sulfur compounds, with a focus on hydrogen sulfide, methanethiol, thioacetates, disulfides, polysulfanes, the metabolic and chemical pathways that lead to their formation and loss after formation and the chemical and environmental factors that lead to otherwise innocuous sulfur-based compounds being converted to those that have a significant sensorial impact in wine.
Practical strategies to decrease the occurrence or impact of negatively perceived volatile sulfur compounds.