Making wine in a warming world

Grapes don’t ripen the way they used to. As temperatures climb, they are getting sweeter faster.

Winemakers find that by the time the crop achieves the right colour or level of tannins, the grapes contain more sugar. More sugar means heavier, more alcoholic wine. At the same time, drinkers are preferring lighter wines

Dr Roberta De Bei is trialling counter-measures to delay ripening at the University of Adelaide, where she has worked as a research fellow in the School of Agriculture, Food and Wine since she left Italy in 2008.

In some Mediterranean climates, techniques such as removing part of the leaves of the vine while the grapes are ripening have been found to delay sugar accumulation in the berries by up to two weeks without affecting other properties of the grapes.

The technique relies on the fact that a reduction in leaves by at least 30% is expected to reduce photosynthesis and hence the production of sugar that is then concentrated in the berries.

“Most of the studies are coming from Italy and Spain,” Roberta says. “but we want to know if these techniques will work in Australia.” She is working with Associate Professor Cassandra Collins and researchers at the universities of Adelaide, Melbourne, Sassari and Pisa (in Italy) to try these methods in Australian Semillon and Shiraz grape varieties.

While a delay in ripening of ten days in Semillon and 20 days in Shiraz was observed in the second year of the study, the overall results suggest that high seasonal climate variability and rainfall from year to year mean the effect of the techniques trialled are not consistent each season.

“Further research in this area would provide more conclusive results,” Roberta said.  “We are now trialling the removal of up to 50% of the leaves earlier in the season and extending our research to other varieties.”

The research has been published in the American Journal of Enology and Viticulture.