This nice little video combines a bit of physics, chemistry, and biology as it discusses how bubbles form in champagne: the gas is carbon dioxide; carbon dioxide forms from the fermentation of sugars by yeast — it’s a byproduct of the reaction that produces alcohol; the bubbles form at tiny flaws or bubbles in the glass (so you can put in tiny flaws to control where the bubbles form); the bubbles rise because the gas is less dense than the liquid around it; and the bubbles expand as they rise because the pressure of the liquid becomes less and less the closer to the surface you are.