carbon dioxide
A colorless, odorless, incombustible gas. carbon dioxide (CO2) is one of the two by-products of fermentation, the other being alcohol. yeast acts on the natural grape sugar and converts 40 to 45 percent of it to carbon dioxide, which in most cases escapes into the air. In the production of sparkling wines, however, carbon dioxide is purposely trapped in the wine to create effervescence.
The New Wine Lovers Companion, 2nd Edition, by Ron Herbst and Sharon Tyler Herbst. Copyright © (1) 2003, 1995 by Ron Herbst and Sharon Tyler Herbst. Reprinted by arrangement with Barron's Educational Series, Inc.