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Inquiring Winemaker TIM P A T TERSON Carbon Dioxide in Wine: It's a Gas! C arbon dioxide is no stranger to winemakers: It floods the cellar during fermentation, serves as a blanketing layer in tanks to keep oxygen at bay and makes sparkling wines sparkle. But in still wines, at the sub-bub- ble level, it doesn't get much respect. That is a shame, since the level of dis- solved carbon dioxide in the bottle can have a major impact on how a wine hits the palate. Too little can render white wines flat from day one; too much can make reds harsh and tannic. And since the level of dissolved CO2 is significantly affected by numerous environmental variables—tem- perature, frequency of racking, sparging with other gases—it can easily go too far up or too far down without the winemaker doing anything directly about it. The basics of carbon dioxide's sensory role high on most small North American produc- ers' checklists, if it's on there at all. Maybe it should be, since these often- overlooked leftovers from fermentation can pack a punch. have been well established for some time, and methods for measuring and managing it are easily available. But except for the mega-scale industrial wineries that monitor and tweak nearly every molecule in their vats, CO2 isn't Highlights • The level of dissolved carbon dioxide in wine can have a significant sensory im- pact, but it gets relatively little attention from most small producers. • Different varietals and wine styles work best with different levels of CO2 . • Testing for at least ballpark CO2 levels can be helpful to winemakers, but al- ways in conjunction with careful tasting. The gospel according to Peynaud The reference text for understanding the sensory impact of dissolved carbon dioxide in wine is French enologist Emile Peynaud's 1983 classic, "The Taste of Wine." In one context after another, he presents CO2 as a overly tannic. If dry white wines are too low in CO2 lift the aromatics and add freshness and verve, especially to whites; in big reds, on the other hand, even much lower levels of CO2 double-edged component capable of mak- ing wine sing or making wine bite. In the proper balance, Peynaud argues, CO2 can get duller; but for sweet whites, lower lev- els of CO2 can make a wine hard, acidic and , they start life dull and quickly enhance richness. form of carbonic acid. Dissolved CO2 con- tributes to titratable acidity, but at the lev- ups the perception of acidity—and well it might, since CO2 66 Wines & Vines MAY 201 1 Immunotest2 TR.indd 1 06/04/11 09:16 In all these cases, the presence of CO2 in solution takes the