Charles Sturt University  PhD student Julia Gouot, from the National Wine and Grape Industry Centre (NWGIC) is studying the impact of heat waves on the grapes’ physiology and composition.

She is looking at 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 heat waves at the bunch and whole-vine levels, observing the impact of high temperature, 40 to 45 degrees, and extreme temperature, above 50 degrees,” Ms Gouot said.

“We’re interested in seeing how that influences compounds such as phenolics in berry skin and seeds 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 heat waves on berry survival and quality to guide decision making.”

A separate project for the NWGIC – an alliance between CSU, NSW Department of Primary Industries and the NSW Wine Industry Association – is looking at the effect of sunburn on wine grapes.

“Sunburn can affect up to 15 per cent of winegrape berries in Australia in any given season,” researcher Joanna Gambetta said.