Here's the thing about beer: almost all of it is best fresh. Nine times out of ten, there is no benefit whatsoever to letting that beer get any older than it is at this very moment.
So then does the term "beer cellar" even exist? Well, there are exceptions to this rule. While all beer will evolve over time in the bottle, can or keg, there are a handful of brands that will change for the better. Essentially, allowing your beer to age under ideal conditions can mellow, pleasantly oxidize, and develop the beer's flavors in a truly delicious way.
Now, some will try to tell you that anything above X% alcohol can benefit from cellaring for up to Y years. Sadly, it isn't that simple. While it is true that highly alcoholic or acidic beers do generally fare better over time, there are no catch-all rules for beer aging. If you decide to start a beer cellar, it should be done in the spirit of self-education and experimentation, not with the intention of improving everything you stick in there. That is a recipe for disappointment.
Here are a few tips and a bit of advice to get your beer cellar started.
1. Start with beers that have a good chance of improving. Stronger beers do tend to fare better than the alternative, as do highly acidic ones, but there are countless exceptions. Try starting with barleywines, old ales, imperial stouts, Belgian strong dark ales, and lambics—proven candidates for improvement over time—and branch out from there. Keep in mind that hop flavor and aroma is one of the first things to fade when you age a beer, so IPAs and similar ilk (while strong) may not be the best candidates for improvement.
2. Always taste the beer fresh. What's the point of seeing if something will improve if you don't know what it tasted like fresh? Ideally, buy at least 3 bottles when cellaring a beer—one to drink right away, one to drink later, and an extra in case the beer needs more time after you try the second bottle. One of my favorite practices is buying a case I know can age very well and drinking a bottle every few months or so over the course of years and seeing how it develops. Hair of the Dog's Adam is a perfect beer for this—I've had 16 year old bottles that were great.
3. Start tasting at around 6 months. This will give the beer enough time to develop significantly enough such that it will be interesting, but not enough to risk overshooting the Peak Deliciousness Point. From there, you can gauge how fast the beer is developing, and if you'd like to drink your remaining bottles now or let them continue to evolve.
4. Store your beer upright. While wine is traditionally stored on its side, it is generally better to store beer upright. This will keep any sediment held firmly at the vessel's bottom while minimizing the beer's surface area contact with the oxygen-containing headspace in the bottle.
5. Keep bottles dark. Light is one of beer's worst enemies. Keeping bottles dark is absolutely essential to protecting the beer from light degradation that can skunk and otherwise lessen the quality of your increasingly tasty beverage.
6. Keep bottles cool, and consistently so. 50 to 60 degrees F is best. Fluctuations in temperature will hurt your beer, and throwing your beer in a 75 degree closet will speed up the production of a cardboardy flavor compound known as trans-2-nonenal. Not good. I'm not going to suggest everyone goes out and buys a high-tech aging fridge, but look for the coolest, darkest place place in your house. If you have a basement, you're lucky.
Tell us: do you have a beer cellar? What beers are you saving to taste later? What have your favorite cellared beers been?