I drink mixed drinks infrequently, so it takes me a while to go through a bottle of rum, whisky, or vodka. Thus far I haven't noticed a problem with, say, a two-year-old (opened) bottle of any of these, but on the other hand, if they were degrading slowly I might not notice. Does the flavor of hard liquors change over time after the bottle has been opened? (Assume it is tightly recapped after use.) And are there any safety considerations?
I have never head of safety concerns, especially if the bottle is properly recapped, but what often is an issue is oxidization, and exposure to sunlight.
It happens much more slowly to liquors than to things like foods or wines, but every time you open the bottle you let oxygen get in, especially so the first opening, which will affect it though its really only slightly. The sunlight has similar affects on the spirits, to a similar magnitude (i.e. not very much).
Vodka for example should be fine nearly indefinitely if properly kept, but whiskeys, gins, tequilas, rums, and the more complex liquors will degrade (again, only slightly and slowly). I've heard people say they can taste changes in 3-4 months, others years, but even if you have a bottle around for a year or two I really wouldn't have any concerns (I'm kinda skeptical of the 3-4 month people)
I've had whiskeys and rums left around for 4-5 years after opening. They weren't great spirits themselves, but there was nothing unpalatable about them.
If you are concerned, I would just keep your spirits in a cool, dry, dark space and then you probably don't have to give it a second thought.
Wow, your question bring back memories.
My grandfather collected bottle of various hard liquors while in the military (World War II) and had them in a liquor cabinet in the basement. After the war, he stopped drinking and there in his cabinet where was a large number of bottles that were almost all opened, yet I would guess were at least 75% full. Occasionally we would have some at Christmas or some other occasions and they seemed quite fine to us back in the day. Some of his bottles were decades old.
But in reality how long will hard liquor remain good?
There's no need to replace those decades-old bottles of gin and whisky. Distilled spirits like vodka, rum, whisky, tequila and gin don't ever spoil — even after opening. The taste, color or aroma may fade over time, but it'll hardly be noticeable. Keep the bottles tightly closed and store them in a cool area away from direct heat or sunlight. - Forever foods: 10 cooking staples that can outlast you
How Long Do Spirits Last?
The easiest class of booze to keep, sprits will generally last forever—although that statement comes with a couple of caveats.
Spirits are usually high enough in proof that their alcohol content will preserve them indefinitely. Of course, because of that same alcohol content, you need to be sure to store them in a cool place. Above a radiator is not the right answer.
Spirits do not "get better" in the bottle; they do not generally develop additional flavors in glass. For a spirit to age in the sense that we mean when talking of aged spirits, they need to age in wood. Glass doesn't impart additional flavor or aroma.
Two things will happen to spirits in glass, however: oxidation and evaporation. As the booze reacts with oxygen, its flavors diminish over time. For short periods, this effect is subtle. Keep an open bottle of bourbon around a couple of months, and you probably won't notice any difference. Store it for years, though, and you might find it tastes a little flatter than when it was brand new.
A small amount of evaporation from the bottle is inevitable and unavoidable; to make sure it stays just a small amount, though, remember what I said before: keep the booze in a cool place.
But say you have a special bottle, something you want to keep around for a long time, and sip slowly over years. How can you protect the stuff inside? The simple answer is, transfer it into a smaller bottle. A few remaining ounces of that perfect single-malt, stored in its original bottle, will continue to react with the oxygen that fills up the bottle. A smaller vessel simply has less room for that spirit-snuffing oxygen.
Now, is this necessary? Probably only if you're a collector or true spirits enthusiast. I doubt most drinkers would notice. - How Long Do Spirits Last? by Michael Dietsch
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It depends on where and how long you store them.
In a cabinet or in a showcase with glass windows, the light is affecting the aging and changing progress. I made experiences with 15 year old Whiskeys, Bourboun and Scotch which were very much affected because they were opened before(to the point where it wasn't drinkable anymore).
In your case, it is important how long you store your bottle, if it is under one or two years, from my experience, you should be fine because high percentage beverages last very long.
As a reference, the same goes for wine but in a much lesser quantity of time.
I hope this helps you a bit.