ACS Chemistry for Life

Champagne may be the elixir of celebration, but for something so closely tied to joyous events, champagne is mercilessly encumbered by laws. The Appellation d’Origine Contrôlée outlines 35 of these rules conceived to uphold the quality of Champagne wines. It also defines the region of Champagne, an 84,000-acre area about an hour’s drive east of Paris. This demarcation separates champagne from other sparkling wines made with the “méthode champenoise.” According to the appellation, if the grapes weren’t grown in Champagne, the wine isn’t champagne.

From a chemical perspective, though, champagne and all other sparkling wines must conform to just one law, Henry’s law: The amount of gas dissolved in a fluid is proportional to the pressure of the gas with which it is in equilibrium. This dissolved gas–carbon dioxide in the case of champagne–gives the wine its characteristic effervescence. In an unopened bottle, CO₂ gas dissolved in the wine is in equilibrium with gas in the space between the cork and the liquid. Uncorking the bottle releases this headspace gas and disrupts the equilibrium. Following Henry’s law, the dissolved CO₂ leaves the wine via bubbles, reestablishing the equilibrium through effervescence.

Champagne makes its gas naturally during fermentation. Yeast turns glucose from grape juice into CO₂ and ethanol. The same fermentation process occurs in all wines, but valves on the casks let winemakers release the CO₂ so that it doesn’t build up.

Champagne gets its characteristic bubbles by trapping CO₂ gas while in its bottle, where it ferments a second time.

Visit “What’s That Stuff” to learn more about the chemistry of champagne.

Excerpted with permission, Chemical & Engineering News
Copyright © 2004 American Chemical Society