RESEARCHERS at the University of Adelaide have discovered the best methods of delaying grape ripening, leading to better quality and more flavoursome wine.

The research was published in Horticulture Research, titled ‘A systematic review and meta-analysis of vineyard techniques used to delay ripening’ and combined the efforts of researchers from

University of Adelaide with researchers from Italy and California, USA.

Lead author Pietro Previtali, a PhD graduate from the Department of Wine Science and Waite Research Institute, and the Australian Research Council Training Centre for Innovative Wine Production, said the research focused on three common techniques used to delay grapes ripening: the use of antitranspirants, late pruning and late source limitation.

“Antitranspirants are compounds applied to the leaves of plants to reduce transpiration,” Mr Previtali said.

“We found that applying antitranspirants when the grapes started to change colour caused larger ripening delays, and the ripening delay was larger when there were early and late-season applications.

“Late pruning is when pruning is postponed until after the apical buds have burst.

“We found there was a larger delay in ripening when the vines were pruned later in the season, however the technique is less effective on high-yielding vines.

“Late source limitation, which removes a portion of the young leaf area that accumulates sugar during ripening, is likely to be more suitable in red grape varieties with higher sugar levels, while white grape varieties may be harvested too early for this treatment to be effective.

“We also observed larger ripening delays were achieved on high-yielding vines where sugar accumulates slower.”

PhD supervisor, Associate Professor Chris Ford, said higher sugar concentrations in grapes can be caused by a number of factors.

“Increased levels of carbon dioxide in the atmosphere, rising global temperatures and declining rainfalls, can lead to grapes ripening faster than normal,” Prof Ford said.

“This results in higher levels of alcohol, throwing off the balance of the wine and diminishing the quality of the product, while growers may need to postpone harvest altogether.

“This research can hopefully help growers make decisions that will generate higher yields and quality wine.”

The results of 43 studies were examined by researchers, using statistical modelling techniques typically seen in medical and psychological research.