What happens when a bottle of Champagne freezes?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
I put a bottle of Champagne in the freezer and forgot to take it out before it froze. Is it still drinkable?
—Kay, Los Angeles
Dear Kay,
Drinkable? Sure. Enjoyable? Hard to say.
Before we get to why, this is a good opportunity to remind readers that putting a bottle of wine in the freezer is not the fastest way to chill it. The best way to chill a bottle of wine is to submerge it in a bath of ice, water and salt. I never recommend the freezer because not only does it take longer, a forgotten bottle of any wine in a freezer might break as the freezing causes the wine to expand, or the cork may be pushed out.
If your bottle is intact, you can defrost the wine and it won’t be harmful to drink. Still wines will probably taste the same, but frozen-then-defrosted Champagne will likely have a marked reduction in carbonation.
—Dr. Vinny