What gas is primarily responsible for the bubbles in sparkling wine?

• A. Carbon dioxide
• B. Oxygen
• C. Nitrogen
• D. Methane

Answer: (A)

Carbon dioxide is the gas responsible for the bubbles. During fermentation, yeast converts sugars into ethanol and carbon dioxide, and in sparkling wine this CO2 is kept under high pressure so it stays dissolved in the liquid. In the traditional method, a second fermentation in the bottle generates more CO2, which stays dissolved under the bottle’s pressure; in other methods, CO2 can be injected to reach the same result. When the bottle is opened and the pressure drops, the dissolved CO2 escapes as bubbles, giving the characteristic fizz. Oxygen, nitrogen, and methane don’t serve this purpose in sparkling wine, so they aren’t responsible for the bubbles.