What is the fermentation that causes champagne cork to pop?

Here's how it works:

1. Initial Fermentation: After the initial fermentation of grape juice into wine, the wine is bottled with a small amount of sugar and yeast.

2. Secondary Fermentation: This added sugar provides food for the yeast to continue fermenting, producing carbon dioxide (CO2) gas. The bottle is sealed, trapping the CO2 gas.

3. Pressure Build-up: As the fermentation continues, the pressure inside the bottle builds up, often reaching 6-9 atmospheres (that's about 90-135 pounds per square inch).

4. The Pop: When you remove the cork, the built-up pressure quickly releases, creating the characteristic "pop" sound.

So, it's not just the fermentation itself, but the trapped CO2 gas that causes the champagne cork to pop.