Effect of Cluster Temperature on the Composition of Berries Grown Under Field Conditions
Because climate influences grape composition, a considerable amount of research has
been directed towards understanding how grape composition responds to light and
temperature. Studies that have separated light from temperature affects however are few.
This project is investigating the effect of cluster temperature on berry composition.
Using equipment designed to precisely manipulate in-situ cluster temperature,
temperatures were manipulated to achieve daytime cooling, nighttime heating, and a
variation in diurnal temperature range (DTR) while maintaining constant light exposure.
Grapes were monitored for various phenolic compounds (flavonols, flavan-3-ol
monomers, tannins, and anthocyanins), organic acids, and sugars. The results of the
project indicate that the period between fruit-set and véraison is sensitive to temperature.
For tannins, an increase in temperature was associated with an increase in tannin
production and a reduction in average degree of polymerization. During fruit ripening,
berries were much less sensitive to changes in temperature. Finally, a reduction in DTR
led to an apparent increase in the rate of fruit development. The results of this
investigation are designed to provide grapegrowers with information that can assist then
in managing grape components that are important to wine quality.