If you open a bottle of Cognac with friends, is it OK not to finish the bottle?

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Dear Dr. Vinny,

If you open a bottle of Cognac with a group of friends, is it OK not to finish the bottle?

—Monica, Daly City, Calif.

Dear Monica,

I really love the idea of telling my friends they can’t leave my house until all of the Cognac is gone, but that’s not necessary.

Cognac comes from the Cognac region of France, and it is a type of brandy that’s made from double-distilling white wine, then aging it in wooden casks. Because it’s a distilled spirit, once it’s bottled it doesn’t age the same way that wine does in the cellar, and it also doesn't react to oxygen nearly as noticeably as a regular bottle of wine once it's opened.

Once opened, a Cognac will start to fade over time, but that process will be slow and subtle—the decline would be measured in months rather than hours or days. If it takes months or longer for you to get through that bottle (whether or not with the help of your friends who are held captive in your house), the Cognac will eventually lose a little bit of its alcoholic strength to evaporation. The Cognac will remain perfectly fine to drink, but you might start to notice changes in quality and alcohol strength after about six months. If you want to transfer the remaining Cognac to a smaller bottle to eliminate how much oxygen it is exposed to, that would slow the process.

—Dr. Vinny

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