Do ripening grapes need sunscreens?

Do ripening grapes need sunscreens?

The answer to this question and others about the effects of UV radiation on grapes and vines are the subject of on-going study by scientists from the Centre for Viticulture and Oenology at Lincoln University.

“Scientists are interested in the effects of UV on plants because New Zealand receives about 45-50% higher levels of ultra-violet radiation compared with similar latitudes in the Northern hemisphere,” said the Programme Leader, Professor Brian Jordan,.

The study was set up to investigate the effects of UV on Sauvignon Blanc grape chemistry under field conditions in New Zealand.

Results so far show that UV can affect the biochemistry of grape vine cultivars and the resulting wines.

Specifically, UV causes accumulation of polyphenols (compounds that absorb the UV radiation and therefore protect the plant) in the grape skins and this may lead to changes in the properties of the wine, such as ageing and mouth feel.

“Before this study, we also did not know how and where and when the aroma compounds were made but it now seems that methoxypyrazines (compounds that impart the green/green capsicum aroma) are in high levels in the leaves and this has exciting implications for the leaf-berry relationship and canopy management,” said Professor Jordan

In these experiments different plastic filters were placed over the fruit zone of Sauvignon Blanc vines in the Lincoln University vineyard to limit their exposure to UV. Some vines also had leaves removed. Samples were taken from the vines and berries and analysed for the effects of UV exposure and leaf removal on their biochemistry.

“These results improved our understanding of the interactions between the leaves and the fruit, and showed the importance of managing the vine canopy to enhance the beneficial effects on the grapes and the resulting wines,” said Professor Jordan.

“Another very important observation was that leaf removal (a common viticulture practice to reduce disease pressure) altered the amino acid composition in the berries. Retaining the leaves increased the level of amino acids in the berries. Amino acids are precursors for many essential components of grape juice and in the fermentation process to produce the wine.”

An informal (non-scientific) sensory evaluation of these wines revealed that the aroma and flavour of the wines were impacted by the different experimental treatments.

“This demonstrates the importance of managing the vine canopy in order to produce high quality grapes, something New Zealand is gaining a well-earned reputation for,” said Professor Jordan.

The Lincoln-based researchers on this project include Professor Brian Jordan, Senior Lecturer, Dr Rainer Hofmann, Senior Lecturer, Dr Chris Winefield with collaborators, Professor James Shinkle from the USA, Dr Jason Wargent from the UK and Dr Mike Trought from Plant & Food Research.

Support has come from a number of different sources: Lincoln University, Plant and Food Research, wine industry representatives and New Zealand Winegrowers, the Foundation for Research, Science and Technology (FRST) and International Travel Fellowships.

ENDS

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