In an interesting report out of Portugal, Goncalves et al. (2009) wrote that "the impact of elevated carbon dioxide concentration on the quality of berries, must, and red wine (with special reference to volatile composition, phenolic content, and antioxidant activity) made from Touriga Franca, a native grape variety of Vitis vinifera L. for Port and Douro wine manufacturing grown in the Demarcated Region of Douro [northern Portugal], was investigated during 2005 and 2006," in which study grapevines were grown in open-top chambers maintained at either 365 or 550 ppm CO2. The result of that study, in the words of the six Portuguese researchers, was that, "in general, the increase of CO2 did not affect berry characteristics" and "did not significantly change the total antioxidant capacity of the red wines." In fact, they say that "thirty-five volatile compounds belonging to seven chemical groups were identified," and that, "generally, the same volatile compounds were present in all of the wines." Although some of these compounds were "slightly affected," they say "the red wine quality remained almost unaffected." Thus, Goncalves et al. say their study showed that "the predicted rise in CO2 might strongly stimulate grapevine photosynthesis and yield [italics added] without causing negative impacts on the quality of grapes and red wine." And putting their personal stamp of approval on their findings, they state that "the informal sensorial analysis carried out by the researchers" also showed that "wine quality remained almost unaffected."

Well, as the old saw goes, "no news is good news," and so it was ... in the minds and taste buds of the intrepid Portuguese researchers. But others have had even better news.

Working near Rapolano, Siena (Italy), Bindi et al. (2001) conducted a two-year (1996, 1997) FACE study of 20-year-old grapevines (Vitis vinifera L., cv Sangiovese), where they enriched the air about the plants to 550 and 700 ppm (compared to ambient CO2 levels in those two years that averaged 363 ppm, as per Mauna Loa data), measuring numerous plant parameters in the process, including -- after the fermentation process was completed -- "the principal chemical compounds that determine the basic red wine quality." This work revealed, in their words, that "elevated atmospheric CO2 levels had a significant effect on biomass components (total and fruit dry weight) with increases that ranged from 40 to 45% in the 550 ppm treatment and from 45 to 50% in the 700 ppm treatment." In addition, they report that "acid and sugar contents were also stimulated by rising CO2 levels up to a maximum increase in the middle of the ripening season (8-14%)," but they note that as the grapes reached the maturity stage, the CO2 effect on these parameters gradually disappeared. In terms of the primary pigments contained in the wine itself, however, we calculate from the bar graphs of their results that in response to the ~50% increase in atmospheric CO2 concentration experienced in going from ~363 to ~550 ppm CO2, the concentrations of total polyphenols, total flavoniods, total anthocyanins and non-anthocyanin flavoniods in the wine rose by approximately 19%, 33%, 31% and 38%, respectively.

Speaking of the future, Bindi et al. concluded that "the expected rise in CO2 concentrations may strongly stimulate grapevine production [italics added] without causing negative repercussions on quality of grapes and wine," although their data suggest that the ongoing rise in the air's CO2 content might actually slightly enhance the health-protective properties of the wine ... but only if not overused, of course.

References
Bindi, M., Fibbi, L. and Miglietta, F. 2001. Free Air CO2 Enrichment (FACE) of grapevine (Vitis vinifera L.): Growth and quality of grape and wine in response to elevated CO2 concentrations. European Journal of Agronomy 14: 145-155.

Goncalves, B., Falco, V., Moutinho-Pereira, J., Bacelar, E., Peixoto, F. and Correia, C. 2009. Effects of elevated CO2 on grapevine (Vitis vinifera L.): Volatile composition, phenolic content, and in vitro antioxidant activity of red wine. Journal of Agricultural and Food Chemistry 57: 265-273.