Would it not ferment and become even more alcoholic over time? Or does a glass bottle not give the right conditions?
Okay, gonna go all nerdy here, lol.
When making whisk(e)y specifically, it must be made from grains, and the basic process goes like this:
- Harvest the grain.
- If you need to, malt and boil the grain to get it to release its sugars.
- Ferment the sugars released by the grain to create wash, or distiller's beer.
- Distill the wash or distiller's beer using whatever still you want, and however many times you find you need to.
- Put it in a barrel of some kind and let it age for 3 years or so.
When it comes to the aging process, how it works is that microscopically, oak is a lot like a sponge. As whisk(e)y ages a chemical reaction starts where it starts to break down the lignins in the oak barrel over time. The impact imparts some sweet flavors, tannins, and such. A lot of those raw, tobacco or leather notes in a whisk(e)y is actually the impact of the barrel.
During the hotter parts of the year, the whisk(e)y warms up and expands, which pushes the whisk(e)y further into the barrel. If you've ever seen a used whisk(e)y barrel stave, you saw a line going down the stave.
That's how far the whisk(e)y is penetrating into the barrel.
During the cooler parts of the year, the temperature and pressure drops, essentially forcing the whisk(e)y out, bringing along any flavor components as a result of the whisk(e)y breaking down the lignins in the wood of the barrel.
Now, as you can imagine, this can drastically affect the final flavor of the whisk(e)y, and temperature and climate also influences how quickly this happens, as well as the size of the barrel plays a role too.
Generally, in hotter climates, like say Texas and Kentucky, it's essentially getting forced into the barrel more, and since the law specifies that bourbon must be aged in new, charred oak, that type of barrel also tends to have more of a flavor impact. That's why some bourbons, in my opinion, can be overaged.
But with scotch, they also use used oak, and mostly it's ex-bourbon barrels, but in the Speyside region of Scotland, they tend to use old port, wine, and sherry barrels, which is why Speyside scotches tend to be more sweet and fruity in flavor.
Now this doesn't work with glass, because whisk(e)y can't penetrate into glass.
So you can't really age whisk(e)y in a bottle. That's a thing for wine, not for whisk(e)y. Once the distillery bottles it, it's as old as it ever will be, hence why the age statement on the bottle specifies the age of the
youngest barrel used when making the whisk(e)y.
But basically, if the seal on the bottle's good, and it's out of direct sunlight, it can last indefinitely.
But, what eventually happens is that if a whisk(e)y was left in open air, eventually the alcohol will just evaporate away,
then it goes bad.
But as far as whisk(e)y, the minimum required ABV as per the law is 40%, which is far too high for any colonies of any microorganism to survive.
So, yeah, in the bottle, with a nice cork or screw top lid, it's fine. Just keep it out of sunlight, because sunlight can bleach the tannins in whisk(e)y, which can ruin the flavor.