Oxidation’s effects are many: It can darken the color of a beer, cause it to smell sweeter as hop aromas fade and malts oxidize, and even cause particulate matter to appear. Regardless of how well-made and skillfully packaged a beer may be, oxidation is also inevitable—you can slow its progress through proper storage—cold and dark—but there’s no stopping it. Oxidation over time also causes a whole host of changes to a beer’s flavor, some of which are desirable, many of which aren’t.

Heat, light and oxygen are a fresh beer’s three biggest foes. Oxidation is responsible for most non-microbial forms of food spoilage or staling. It’s the same with beer. The presence of excess O2, either in solution or in the beer package, will have detrimental chemical effects on the beer over time. How long it takes for those effects to manifest as undesirable flavors is a question of production process and storage. If a beer was canned or bottled with an excess of oxygen, it will oxidize and stale more quickly. The same thing happens if a beer was subjected to hot storage or temperature swings that force oxygen into and out of the liquid repeatedly.

Does beer expire? In a word: yes. As I like to tell my six-year-old, “Ain’t nothing last forever.” Like almost all consumables—except Twinkies, maybe— beer has a more or less definite shelf life , and a temporal rubicon which, when passed, makes the beer thoroughly unpalatable. But why does beer expire, and how quickly? First, let’s look at the two major causes of beer death: oxidation and breakdown. Then, we’ll consider how one can tell if a beer has gone “bad,” and the few exceptions when extended age in beer can be a virtue.

Breakdown

We don’t think of it often, but beer has structure. It’s a “colloidal solution,” best thought of as "a mixture with properties between those of a solution and a fine suspension (finely 'floating’ matter),” according to Brewers Journal. Which is to say, there’s stuff floating in your beer that you normally can’t see. Much of that stuff is protein, largely derived from malt during the boiling part of brewing, and polyphenols, which come from malt husks and hops. These can, under certain circumstances, join together to cloud the appearance of a beer, presenting as anything from a light haze to chunky floaters.

With the recent trend toward ultra-turbid, sometimes opaque and frankly disgusting-looking IPAs, one could be excused for being a little unclear on what constitutes “good” haze versus “bad” haze. If a given beer is intended to look like a glass full of chicken broth, then clarity is definitely not going to be a good indicator of quality or age. For the vast majority of beers, though, lack of clarity is definitely considered a fault, and “protein haze” was historically a mark of poor process or extreme age. In old beer, especially beer past its prime, oxidation can cause telltale haziness as proteins and polyphenols combine to form what’s sometimes referred to as protein “snow,” which appear as white flakes floating in your beer. There are plenty of good reasons to excuse the floaties, but if you’re expecting a brilliantly clear pilsner and get something that looks like a snow globe, there’s good reason to think it’s just old as hell and has begun to break down.

Tasting Age

All of this is not to say that aged beer is uniformly bad, or that aging beer purposefully is necessarily a bad idea. You may be familiar with the concept of “cellaring” or vintage beer sales or tastings. There are good reasons to lay beer down, but when it comes to doing it in a way that produces a favorable result, that purposeful part is very important. As noted above, time takes a heavy toll on most beers, and relatively few styles are suitable for extended aging. As a rule of thumb, beers light in alcohol, body and color generally aren’t good candidates. IPAs and hop-driven beers especially should be consumed fresh. Hop flavor, aroma and bitterness all begin to weaken and fall off relatively quickly over time.

Beers that improve with age—or at least change in interesting ways—tend to be big. That means they are high in alcohol, heavy in body and bold in flavor. The oxidation effects that cause most of the signature flavor changes in beer manifest well in strong, dark ales. Imperial stouts, for example, can develop flavors of dark fruit, while alcohol warmth and bitter roastiness both tend to recede and become softer. High gravity Belgian ales typically become more effervescent and spicier, while gueuze and mixed-fermentation sours can change in a wide variety of ways over time, becoming funkier and softer if they started life as bright and bracing, for example. Barleywine and old ale are also great candidates for aging, often becoming savory, almondy and Madeira-like as they oxidize. In lighter beers, these oxidation effects are expressed as papery, dead staleness on the palate.

Regardless of the fact that there are beers more suited to aging than others, you may find that aged beer simply isn’t to your taste, which is totally fine. Most beers are meant to be consumed fresh, and virtually no beer leaves a commercial brewery not ready to drink that day. Live in the moment and drink up.

Top photo by Kyle Kastranec, Good Beer Hunting