Optimising colour and tannin composition of grapes and wine
Abstract
Grape flavonoids including anthocyanins and tannins contribute to the colour and taste of wine. The influence of temperature and irrigation on grape flavonoid composition was investigated to determine how fruit composition could be managed in the vineyard.
Summary
The effect of increased temperatures on the flavonoid composition of Shiraz grapes was investigated in collaboration with SARDI researchers at Nuriootpa. Heat was applied to bunches with blowers or to the vine canopy using under-vine tents or chambers at different times through the growing season. Short interval heat applications during the season did not change flavonoid content at harvest. Increased night temperatures, applied after fruit set, hastened berry development and advanced the onset of ripening. However, by the time fruit was harvested there were no significant changes in anthocyanins. We concluded that greater changes in temperature, treatment for longer periods, or more elevated night temperatures may influence anthocyanin accumulation and should be further investigated.
The influence of irrigation on grape flavonoid composition was also investigated in a trial on Cabernet Sauvignon growing in the Riverland. Decreased irrigation reduced anthocyanins and tannins in the skin, while having no effect on seed tannins.
The roles of the three grapevine chalcone synthase (CHS) genes in flavonoid synthesis were elucidated. All three genes were found to have a role in flavonoid synthesis in grapes but they are differentially expressed during berry development and in the different tissues of the grapevine. The grape VvCHS1 gene is primarily
involved in flavonoid synthesis in vegetative tissues and very young berries, while VvCHS2 and VvCHS3 appear to play a role in anthocyanin synthesis.
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