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New research provides insight into managing compressed vintages

RD&A News | March 2021
12 Mar 2021
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Vintage compression can be a tricky issue to manage at this time of the year, placing pressure on winery infrastructure, resulting in reduced yields and in some fruit being harvested with a higher than ideal sugar concentration.

New research provides insight into the dynamics of sugar accumulation in red varieties – and the level at which water addition risks introducing negative wine sensory attributes. The findings will help growers and wineries make better harvest decisions and assist with managing wine flavour and phenolic composition under revised regulations (2017) that allow the limited addition of water to high-sugar musts and juice.

The project – supported by Wine Australia – was split into two sections.

The first investigated the dynamics of grape berry ripening and berry sugar content and the second investigated the impact of must dilution on sensory outcomes in Chardonnay and Shiraz wines.

The ripening study compared increases in grape sugar concentration caused by the import of sugar from the vine to those caused by berry dehydration.

Analysis of Shiraz and Cabernet Sauvignon suggested that Shiraz ceased importing sugar from the vine at 13° Baume and Cabernet Sauvignon at 14.5° Baume.

‘Beyond these values, additional increase in sugar concentration is likely to be the result of fruit dehydration’, said principal investigator Dr Paul Petrie, who undertook the research while at the Australian Wine Research Institute (AWRI). Dr Petrie is now at the South Australian Research and Development Institute (SARDI).

‘Dehydration also results in a loss in yield, which potentially impacts on vineyard profitability’, he said.

The second arm of the project, led by AWRI Research Manager Dr Keren Bindon and Dr Petrie together with Post-doctoral Fellow Dr Bo Teng, assessed wine sensory properties in Shiraz as a function of ripeness (13.5° to 15.5° Baume) and the impacts of must water addition on wines made from later-harvested (15.5° Baume) fruit.

A similar trial was conducted on Chardonnay, where water was added by direct addition to grape musts harvested between 13° and 15.5° Baume.

‘What we found in Shiraz was that phenolics (measured by total tannin and colour) increased progressively with ripeness in both grapes and wines,’ Dr Bindon said.

‘Adding water to late-harvest fruit dropped back wine phenolics, but interestingly their concentration was still higher than in wines made from earlier harvested grapes (14.5° Baume).

‘In terms of sensory outcomes, some beneficial increases in ‘dark fruit’ aroma and flavour, as well as opacity (visual) were seen by delaying harvest to 15.5° Baume. These properties were reduced only slightly with a low level of water addition (8 per cent) – which was applied by running off juice and replacing it with water (i.e. no volume change).’

She said adding water directly at a similar level, or water addition at higher levels (14 –17 per cent), was found to increase ‘cooked vegetable’ and ‘drain’ attributes.

‘These were not clearly defined by changes in wine fermentation bouquet and we proposed that certain “reductive” attributes were exacerbated by higher levels of water addition’, Dr Bindon said. Water addition to must is therefore a simple strategy to control wine ethanol in Shiraz without impacting key properties but should be used in moderation.

Dr Bindon said the research suggested that there was a risk of introducing ‘reductive’ characters in Shiraz with higher levels of water addition, applied by direct addition.

‘This is also associated with decreased phenolics, although some of the gains in phenolics made by delaying harvest are retained irrespective of water addition. For more moderate levels of water addition, it would appear that losses in quality were minimised.’

For Chardonnay the changes in wine sensory properties with water addition were minimal in terms of flavour and aroma, with the only clear change being a drop in alcohol-induced ‘hotness’ perception. 

She said for white wines, the risks in terms of quality loss with water addition were lower, and 15.5° Baume musts could be reduced to 13.5° Baume without critical losses in aroma or flavour.

‘A potentially positive outcome for growers and producers is that they can expect a reduction in alcohol-associated hotness following water addition, which could alleviate some of the issues with higher alcohol wines.’

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This content is restricted to wine exporters and levy-payers. Some reports are available for purchase to non-levy payers/exporters.