Manipulation of sugar accumulation in Shiraz

By Lucinda Heyns

In this project, researchers wanted to gain a better understanding of the relationship between berry sugar concentration and wine flavour and aroma. This can help to identify methods for mitigating accelerated sugar accumulation in a in a warming climate.

Project layout 
Sugar uptake of berries were restricted by peduncle girdling of bunches, performed at three post veraison stages in a Shiraz vineyard. Grapes were harvested separately and berry analysis was done.


Results
-          Restricting sugar uptake at 10–14°Brix had severe effects on the accumulation of a number of amino acids, cytokinins and, by inference, the cellular redox status. Consequently, wine made from these berries displayed changes to a large number of esters, higher alcohols and C13-norisoprenoids, which would potentially result in a substantial difference in wine flavour and aroma;
-          When grapes reached 18°Brix, peduncle-girdling caused only minor modification of berry amino acid concentration and wine volatile composition;
-          By comparing wines made from berries of peduncle-girdled bunches with those made from berries where ripening was delayed by auxin treatments, a small group of volatile compounds was identified that universally responds to treatments delaying sugar accumulation in grapes;
-          The findings suggest that once berries have reached a modest sugar concentration, prevention of further sugar uptake even by an invasive treatment, such as girdling, has minimal impact on wine volatile composition.

Significance of the Study
This study confirms that the manipulation of sugar accumulation can mitigate climate change-related acceleration of sugar-ripeness in warm to hot wine regions, while maintaining the volatile composition of wine.


Image: Shutterstock


Comments