Turning up the heat on grapes

As inland Australia braces for more hot weather, a researcher from the National Wine and Grape Industry Centre is studying the impact of heatwaves on the physiology and composition of Shiraz grapes.

Charles Sturt University PhD student Julia Gouot is examining the effect of high temperatures at different stages of berry development and ripening on Shiraz grape composition, especially tannins.

‘‘So far, my research has examined the impact of three-day heatwaves at the bunch and whole-vine levels, observing the impact of high temperature, 40 to 45°C, and extreme temperature, above 50°C,’’ Ms Gouot said.

‘‘We’re interested in seeing how that influences compounds such as phenolics in berry skin and seeds (tannins, anthocyanins), and sugars and acids in the pulp.

‘‘My current experiment is looking at the impact of high daytime temperatures at different stages of berry growth on the accumulation of phenolic compounds in skin and seeds.

‘‘I will also assess extractability of those compounds under wine-like conditions as heat can affect berry integrity.

‘‘Phenolics can contribute to wine colour and taste or mouthfeel, so it is essential to understand how they are affected.’’

Research supervisor and CSU senior lecturer in chemistry Celia Barril said climate change was likely to result in an increase in frequency and intensity of heat events, as well as earlier occurrences of such events during the grape growing season.

‘‘This will impact on berry development and maturation, and composition by harvest,’’ Dr Barril said.

‘‘It’s hoped the research will give growers and winemakers more information about the impact of heatwaves on berry survival and quality to guide decision making.’’

The NWGIC is an alliance between CSU, NSW DPI and NSW Wine Industry Association.