Store it in the Refrigerator This is key. Once open, your vermouth needs to be stored in the refrigerator. It’ll stay in good shape for about a month, and then in passable shape for about two months after that. If you can’t use it up within three months, invite some friends over, or give it away.
How long is vermouth good for unopened?
about 3 to 4 years
Vermouths are great fresh, but that doesn’t mean they can’t sit a few years in the pantry or your wine cellar. Generally speaking, to get the best quality you should use the vermouth within about 3 to 4 years of bottling. If there’s a best-by date on the bottle, just add 2 to 3 years to it, and you’re good to go.