how long will unopened cooking wine last?

First, you say "cooking wine" -- if they actually say that, then they contain lots of salt and sometimes other preservatives - so that they cannot spoil!! Well, maybe in a decade, if they are open! "Cooking wines" are always lesser wines that you wouldn't want to drink. Would you add any other ingredient to your recipe, if it was nasty?

Second, if you are using the term "cooking wine" in a more common sense, then your wines are good to use. Unopened sherry, marsala and expensive burgundies will keep for five to ten years, at least. Unopened inexpensive burgundy will be could for two or three years. Once they are open the sherry and marsala will still be could for months, the burgundy for only a week or two (in the frig).

Finally, know your ingredients before you cook -- taste the wine, if you don't like it toss it.

Does Cooking Wine Go Bad

Does Cooking Sherry Go Bad

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I agree with Chef Paul including storing above the fridge. Champagne like all wines should be stored in a cool place, above the fridge is normally too warm an area. Once opened you can store it for about 24 hours if you use a champagne stopper. If it goes flat before you finish it you can do what Martha Stewart says, which is to freeze it into cubes for latter use in cooking.

I'm not sure either, but what you could do is chop up an onion, saute and then deglaze with the wine to make carmelized onions. If they taste ok, the wine is ok. The worst that can happen is that it turned into vinegar and I use balsamic vinegar to make my carmelized onions.

Good luck!!