Hunting for "dusties"—the name used to describe old and forgotten bottles of booze that languish unopened in backwater liquor stores—marries the thrill of discovery and the smug satisfaction of scoring a good deal. And while the shelf life of beer and liquor vary drastically—whiskeys can sit around for decades, but most beers stale within months—in the last 30 years, craft beers capable of aging have crept from limited markets onto the shelves of distributors and bodegas pretty much everywhere. And just like liquor dusties, beer dusties are out there, on sale, waiting to be found.

... bargains abound in stores that try to sell the right beers to the wrong market.

But tracking down these bottles takes a little luck and a discerning eye. Shops with knowledgeable clientele won’t keep desirable bottles long, but bargains abound in stores that try to sell the right beers to the wrong market. They’ll have last year's Anchor Celebration Christmas release, or a bottle of barleywine that, for whatever reason, has been maturing in the darkness of a cool storeroom for 18 months. Pick up a couple of these and you've got the beginnings of a cross-year comparison of what happens to big beers as they are refined by time—what beer geeks call a vertical tasting.

The best hunting grounds are distributors or stores that move ample mass market booze but also carry craftier stuff. The bulk of their business is selling cases of cheap lager, so they’ll pay less attention to a stray craft bottle. For them, these extras just take up space. Good places to look include chains like BevMo!, as well distributors in cities (I’ve had luck with distributors in Inwood and Sunset Park in New York City). Corner stores and bodegas are adding more craft beer to their shelves, too, and not all of the bottles sell before they go out of season.

But note, sometimes a bottle will appear perfect, though the contents within might be off. I recently picked up a fruit lambic, Hanssens Experimental Cassis, that was half price and looked to be stored acceptably. But when I popped it open, there was no enticing hiss of escaping CO2—always a bad sign. In the glass it gave off a miasma much like the smell of untreated sewage. (Never give something like that a taste test, by the way.) Other times, though, a bottle will be a gem that inspires further hunting. Not long ago I came across a great find: several 2013 Brooklyn Brewery Black OPS for $10 each. The beers had mellowed a bit, with some of the tannin and harsher alcohol notes falling from prominence, replaced on the tongue by a maltiness beginning to be reminiscent of port.

Ready to hunt? Keep these guidelines in mind when perusing dusty beers:

Hops fade quick. And when they’re gone, they leave behind insipid, sad beer. A Heady Topper from 2012 will show little of the zesty sparkle that makes a fresh one sing. So, avoid IPAs and other hop-centric brews that are more than three months old. (Really, with the options available today, no one should drink hoppy beers older than a month, but that's a different topic.) Boozier is better. Higher alcohol content gives beer the resilience to stand up to time, and imbues it with a body that can take on a more complex shape with age, as opposed to going stale. Most times it is best to avoid beers under 8 percent ABV that are more than six months old. Imperial Stouts (every brewery makes one) age well because they are boozy. Darker brews last longer. This is not always the case (certain pale sours and lambics, especially gueuze, are aged for a year or more before they're even bottled for sale, and continue to mature afterwards), but it tends to be a good rubric to follow. Again, big stouts are a safe bet. Barrel-aged is a plus. Beers that are made to spend time in oak are crafted with an eye toward aging (in order to hold up to months or years in a cask, they're often big and malty), so they’re more likely to last or even improve in the bottle. These types of brews also tend to have the most fanboys, so they often command a premium and don’t stay long on shelves. Though once at a distributor in Inwood, in upper Manhattan, I did come across bottles of Goose Island Bourbon County Stout going for around $2 a piece. A tasty, tasty steal. Dark glass or cans only. Skip any beer that is packaged in a clear bottle. UV light destroys the flavor of beer (when people say "skunked," they’re talking about light-struck beer). Clear glass lets through light in all its brightness, meaning that Coronas, Pacificos, High Lifes, or whatever local piss lager on offer will taste like soggy cardboard after even a couple hours in the sun. Size doesn’t matter. And, generally, neither does the capper. Sierra Nevada Bigfoot, a barleywine, commonly comes in 12 ounce bottles with bottle caps, and Cascade Brewery’s complete line of sour ales comes in 750-mL bottles with Champagne corks. Both lend themselves to aging, and both should be grabbed whenever they’re found.

Examine bottles that meet most of these criteria and appear to be stored correctly— away from light and in a cool place. While it's not always possible to tell how a bottle has been treated for its entire existence, the way it's kept in a store is a good indication. Skip bottles in hot rooms and in direct sun. But if a bottle is stationed in a relatively cool, dark spot, it's worthwhile to check its birth date.

Most beers have some sort of date stamp (look on bottlenecks or can bottoms; there are websites that spell out where to look for virtually every brewery in the States), either a simple month, date, and year, or a four-digit Julian date. The latter can seem opaque, but they are simple enough: the first digit is the last digit of the year the beer was produced, and the following three are the sequential day it was, from 001 to 365 (366 in a leap year): February 2, 2014, would be 4033.

As long as a beer contains eight percent ABV and has been well kept, it will last for half a year or longer.

As long as a beer contains eight percent ABV and has been well kept, it will last for half a year or longer. Less potent styles, like brown ales or standard stouts with ABVs of six percent or lower, start to fall in quality after about six months, even in the best conditions. Leave them for someone else. And, as mentioned above, anything that is getting flavor from hops should be drunk as fresh as possible, preferably within a month of bottling. Picking up budget IPAs is sure to result in disappointment—I’ve done it many times to do side-by-side comparisons of fresh and old beers. Unless you’re feeling curious about how flavor falls off, there’s no point in drinking an old IPA.

At any rate, these are bottles of beer, so they are an affordable gamble. Even the fanciest 750-mL bottles cost little more than $20 when they are priced to move. So go find some.