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Dear Dr. Vinny,
Where do the bubbles in sparkling wine come from?
—Anush, Geisenheim, Germany
Bubbly wine, just like beer and soda, gets its effervesce (bubbles) from carbon dioxide gas. You can either add carbon dioxide or you can trap it—it’s a byproduct of fermentation after all. Sparkling wine made in the traditional method goes through the labor-intensive process of trapping the gas, which is pretty neat.
Perhaps the most important part of the process of making sparkling wine (the part that makes the bubbles!), is the secondary fermentation, which takes place inside the bottle. The winemaker adds a solution of sugar and yeast cells to the bottle of wine and seals it up tight. As the yeast cells consume the sugar, carbon dioxide is produced. Once that secondary fermentation is complete, the bottles are stored upside-down, so that the solid byproducts of the secondary fermentation (mostly dead yeast cells) can be collected in the neck of the bottle and quickly removed in a process called disgorgement, which is when the bottle is sealed with the cork that we'll eventually pop.
The pressure inside a sparkling wine bottle can be more than double that of the pressure in your car tires. That's why sparkling wine bottles can pop so explosively, especially if they aren't properly chilled—carbon dioxide is more soluble at colder temperatures.
Once in your glass, the bubbles form at “nucleation sites,” which can be tiny, imperceptible irregularities or even particles of dust. Some Champagne flutes have a built-in scratch in the bottom, specifically for generating that beautiful bead of bubbles snaking their way to the surface!
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