stale beer
Beer samples from a sensory tasting panel at Widmer Brothers Brewing Co. Photo by Jeff Alworth.

Not long ago, I got an email describing a familiar experience:

I poured a Ballast Point Sculpin IPA down the drain because it was stale (rotten pineapple and cardboard). That makes 3 IPAs in the last month I’ve poured out.

We’ve all been there, inadvertently picking up a stale beer. At the moment it leaves the conditioning tank, beer is in a highly unstable state—sort of like a loaf of bread the moment it comes out of the oven. At the moment of a beer’s release, the brewer has managed to excite all the flavor and aroma compounds so that they are at their most vibrant. (It’s why another, opposite experience, is also common: visiting a brewery and discovering a beer you heretofore thought was “meh” to be a triumph of flavor.) A technical paper describes this moment, in masterfully dry, sciencey syntax:

Chemically, beer can be considered as a water-ethanol solution with a pH of around 4.2 in which hundreds of different molecules are dissolved. However, the constituents of freshly bottled beer are not in chemical equilibrium. Thermodynamically, a bottle of beer is a closed system and will thus strive to reach a status of minimal energy and maximal entropy.

Maximal entropy: in sensory terms, that’s not good at all. Those chemicals, interacting with each other (and especially with oxygen, the brewer’s nemesis), conspire to turn a vivid, fresh beer into something dull and muddy. Scientists are only just beginning to understand the mechanisms, and there is a lot left to learn. (In fact, when I asked hop researcher Tom Shellhammer if he knew what caused hop flavor and aroma to degrade, even he didn’t know: “Loss of flavor once in the bottle; that is much more complicated and not much is known as far as I can tell.”) But whether we know the science or not, we know what stale, entropic beer tastes like, and it ain’t no good.

Breweries Monitor Staleness Like Hawks

Every morning, a sensory panel sits in a small clean room deep inside the Widmer Brothers Brewing Co. Tasting panels are not widely-discussed, but most larger breweries have them. At Widmer, training to become a member of the panel takes a full 40-hour week of sniffing, sipping, and swallowing. Over time, potential panelists become attuned to characteristics like ethyl acetate, diacetyl, and isovaleric acid. By the time they’re finished, those certified as “trained” or “expert” will be able to identify dozens of different flavor and aroma compounds that might compromise their beer, usually at levels of just a few parts per million.

On the day I visited, the panel was doing a session of “go/no go,” tasting every batch of beer that will leave the brewery to ensure it was up to their standards. If you’re harboring the secret notion that your palate is something special, I encourage you to find a tasting panel in order to rediscover your humility. At Widmer, they rate beers from one to five, but no beer ever gets a five—that’s like a platonic ideal of beer. Instead, they sniff and swish and start ticking off subtle compounds few laymen would notice. (I certainly didn’t.)

why is my beer stale
Expert tasters can identify dozens of different flavor and aroma compounds that might compromise their beer. Photo by Jeff Alworth.

At one point, a growler of the Widmers’ imperial IPA came around. Beer arriving in a growler has usually come from a bright beer tank, the step before packaging. As I poured out a portion and sampled it, people started murmuring around the table. Someone flagged the beer as a “2”—a problem—so the group went around one by one, explaining what they tasted. To a person, everyone identified the same issue: staleness. Once I knew what to look for, I could see what they were talking about; the beer didn’t have that buoyant zing I recalled.

In fact, this was not a part of the go/no-go process. The leader of the tasting panel was running a secret test on his panelists. He’d gotten an 11-week old sample from the brewery’s pub that was about to be pulled and he wanted to see if his tasters could tell. They easily passed the test. That beer had been chilled since birth and stored in a keg—the most stable package for beer—and yet it was showing signs of degradation less than three months after it left the brewery. Even a lumpen palate like mine could appreciate it.


These are two things we know: beer is perishable and goes stale quickly, and breweries work very hard to fight this natural process (you could make the argument that modern breweries are designed to accomplish two goals—making beer of course, but equally, making stable, low-oxygen beer with longer shelf life). Which brings us back to my reader. If beer is perishable and breweries know this, why is stale beer such a problem? The very interesting answer to that question will be the subject of next week’s post.

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Jeff Alworth is the author of the forthcoming book, The Beer Bible (Workman, 2015). Follow him on Twitter or find him at his blog, Beervana.