Charles Sturt University (CSU) research is giving winemakers new insight into how timing the use of copper can work more effectively to remove an unpleasant smell that’s sometimes created during fermentation.
CSU senior lecturer in wine chemistry Dr Andrew Clark said, 'During the fermentation process, sometimes a tiny amount of hydrogen sulphide, or rotten egg gas, can be produced.
'The unpleasant smell can be removed by winemakers adding very small amounts of copper to bind with the hydrogen sulfide and remove the smell. The new compound, copper sulfide, is then removed from the wine.'
The research at the National Wine and Grape Industry Centre (NWGIC) at CSU in Wagga, funded by Wine Australia, found:
- copper added early in the production process, when protein from the grapes is still present, is more easily removed
- copper added late in the production process doesn’t bind as effectively and it is harder to remove
- if significant copper sulfide is left in the wine, the copper and hydrogen sulfide are not inert and copper can still be active in catalysing less desirable reactions, and
- adding copper just before bottling ‘just in case’ is counter-productive.
Dr Clark said the research is providing winemakers with valuable information about the most effective time to add copper if it is needed.
The researchers, Dr Clark, PhD student Ms Paris Grant-Preece from CSU, Ms Natalie Cleghorn, a former CSU student who works for Yalumba, and Professor Geoff Scollary from The University of Melbourne have been recognised for their work.
Their research paper, ‘Copper(II) addition to white wines containing hydrogen sulfide: residual copper concentration and activity’, was named the Australian Society for Viticulture and Oenology's Oenology Research Paper of the Year for 2015.
Dr Clark said 'This project is a good example of how the wine sector and Charles Sturt University can work together in addressing an industry issue.'
Further research about metals in wine is being conducted at CSU, in collaboration with the Australian Wine Research Institute.