Vine grapes

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

“Scientists are interested in the effects of UV on plants because New Zealand receives about 45–50% higher levels of ultraviolet radiation compared with similar latitudes in the Northern hemisphere,” Professor Brian Jordan says.

Results so far show that UV can affect the biochemistry of grape vine cultivars and the resulting wines. 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/capsicum aroma) are in high levels in the leaves, and this has exciting implications for the leaf-berry relationship and canopy management,” Professor Jordan explains.

Different plastic filters were placed over the fruit zone of Sauvignon Blanc vines in the Lincoln University vineyard to limit their exposure to UV. Leaves were also removed from some vines. Samples were then taken from vines and berries and analysed for the effects of UV exposure and leaf removal on their biochemistry.

Leaf removal was found to alter the amino acid composition in the berries. Keeping the leaves increases the level of amino acids that are precursors for many essential components of grape juice and in the fermentation process to produce wine.

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