A vine’s water potential can also have an effect on berry composition and aroma compounds, says Dr. Andrew Reynolds of Brock University in Ontario, Canada.
In his research, Reynolds used Global Positioning and Geographical Information Systems to map the distribution of leaf water potential (measured in – bars) within nonirrigated vineyards in the Niagara, Ontario, area.
Reynolds and his colleagues found that sections of the Riesling vineyards with the lowest water potential had the highest free and potentially volatile terpenes and the wines were consistently different than the other vineyards. Generally, the high water potential zones were more acidic and citrusy and the low water potential zones tended to have more apricot and peach aromas. Vineyards under the most water stress had the smallest vine size and berry weight.
In Cabernet Franc vineyards, he found similar sensory trends. The vineyards in the high water potential zones had more green bean and bell pepper aromas and more riper-fruit smells in the lower water potential zones.
He emphasized that low water potential doesn’t necessarily mean that the vines are under water stress. The low water potential zones in the blocks studied were, in most situations, no less than -12 bars on average, which is considered mild water stress, he added. "I don’t advocate full-on water stress.
"Long-term water stress may be harmful, while low water stress appears to be beneficial," he stated.
As more is learned about what influences terpene levels in grapes, he sees opportunity in the future to segregate wine grape blocks based on such characteristics as their aroma compounds and terpene levels and harvest such areas separately for different wine styles.