Sparkling wines delight by emitting bubbles that catch the light and prick the tongue. The bubbles come from the wine’s considerable dissolved reserves of carbon dioxide gas, a by-product of yeast metabolism that ordinarily escapes into the air from the surface of the fermenting wine. To make a sparkling wine, the wine is confined under pressure—either in the bottle or in special tanks—so that the carbon dioxide can’t escape as it’s produced, and instead comes to saturate the liquid. A bottle of Champagne holds a gas pressure of 3–4 atmospheres, somewhat higher than the pressure in car tires, and contains about six times its volume in carbon dioxide!