Every tasting party ends with the same leftovers: three or four bottles, each somewhere between full and nearly empty. The good news is that none of them will go bad in any sense that matters for your health. The less good news is that some of them will get duller, and it's predictable which ones.
Spirits don't age in the bottle
Whisky, rum, tequila, and mezcal stop maturing the moment they leave the barrel. A 12-year-old bourbon that sits in your cabinet for five more years is still a 12-year-old bourbon. At 40% ABV or higher, nothing can grow in it, so an opened bottle is safe to drink indefinitely. The question is never "is it still safe" but "does it still taste like it did."
Air is the problem, not time
Once a bottle is open, the empty space above the liquid holds air, and every time you pour, fresh air replaces what you took out. That air slowly oxidizes the spirit and lets the lightest aromatics escape. The rate depends almost entirely on how much air there is relative to liquid.
A bottle that's still mostly full can sit for a couple of years with little you'd notice in the glass. A bottle down to its last third has far more air than whisky, and that's where you start losing the top notes: the fruit and floral edges fade first, leaving something flatter and more one-note. Treat that as rough guidance, not a rule.
How to store what's left
- Upright, always. Wine is stored on its side to keep the cork wet. High-proof spirit does the opposite: constant contact can break down a cork and taint the whisky.
- Away from light and heat. A dark cabinet beats a sunny bar cart.
- Shrink the headspace. If a good bottle is down to its last few inches and you aren't finishing it soon, pour it into a small, clean glass bottle that it fills to the top. This is the single most effective thing you can do.
The real exception is anything that isn't a straight spirit. Cream liqueurs have a printed best-by date for a reason, and vermouth is wine: once opened it belongs in the fridge and fades within weeks.
Use the dusty bottle
This is why our Candy & Whisky kit is built around a bottle you already own. The half-empty bourbon from two holidays ago is almost certainly fine for The Sweet Match, and a party is the best way to finish it before it fades further. If you suspect a bottle has gone flat, pour it next to a fresh one and taste them blind: the blind tasting method settles the question in two sips.