How To Keep Beer From Going Bad

You crack that delicious brew. You're salivating. You take a deep swig and... what the hell is that? Pepé Le Pew? A flatulent egg farmer? No. It's your precious beer and it's gone bad -- skunked beyond recognition. How could this happen?

More importantly, how could you have prevented it?

You've made it through the long week and it's time for Happy Hour, Gizmodo's weekly booze column. A cocktail shaker full of innovation, science and alcohol. If it stinks don't drink.

The Science Of Skunk

You may hear friends use the word skunky to describe several nuances that can ail a lager. Wrong. Skunky is specific. It does not mean flat. It does not mean it tastes stale, sour, bitter, or metallic. Skunky means skunky, as in it literally smells and tastes like a skunk. (Don't pretend you've never tasted skunk, you dirty liar.)

That is caused by a very specific chemical compound: 3-methyl-2-butene-1-thiol, or what Dr Malcolm D Forbes, professor of chemistry at the University of North Carolina calls "skunky thiol". Why? Because it's very similar to the compound found in a skunk's notorious glands. These chemicals are called mercaptans and they contain a high amount of sulfur. We humans are extremely sensitive to mercaptans, and we're able to smell and taste them down to just a few parts per trillion.

Okay, so that's disgusting, but how did these chemical compounds get into your normally delicious beer?

It Isn't Heat

One of the most pervasive beer myths is that taking a cold beer out of the fridge, letting it warm up, then putting it back in the fridge causes it to get skunked. This is 100 per cent false. A change in temperature -- especially such a small change -- cannot account for that chemical reaction. Beer being warm over a period of time can and will affect the flavour (more on that in the minute), but remember that skunkiness is the flavour of a specific chemical compound, and heat fluctuation does not create it. So what does?

It's Light

Skunking is caused by exposure to light. End of story. Well, not really. How it happens is simple: Beer is flavoured with hops. It's a bittering agent that helps protect the brew from bacteria, and it's been used for centuries. Reports of light degrading beer date back to 1875, but it wasn't until 2001 when Dr Forbes at UNC figured out how and why, exactly.

Hops, are light-sensitive and the three main compounds in them identified as being light-sensitive are called isohumulones. When attacked by either visible or ultraviolet light, these break down to make reactive intermediates, known as free radicals. These lead to the offensive taste and skunky odour.

This is why lighter, less-hoppy beers are generally less susceptible to skunking -- there's less in them that can skunk. That's little solace to those of us who enjoy a smack in the mouth from a double-IPA. But fear not. Hop-lovers can take preventative action.

How To Avoid The Stinker

  • 1. Storage. If you aren't keeping beer in your refrigerator (which is where it definitely should be), store it in a cool, dark place. Obviously, sunlight contains a ton of UV rays, so avoid that. But florescent lights pump out UV rays, too. It's a very small amount compared to sunlight, but if those lights are often shining on beer stored outside a fridge, it may be enough to produce the undesirable effect.
  • 2. Packaging. Clear glass is the worst at filtering UV light. Green glass is a little bit better. Brown and amber glass, however, do a very good job of filtering UV, though you still want to minimize exposure to sunlight. Cans are the best -- virtually no light can get through them at all. A lot of great beers come in cans now, and no, they don't taste metallic. They taste as they would coming out of a keg (which is also skunk-proof). That said, if you buy a 12-pack and it's all closed up in cardboard, it's almost certainly OK, even if it's in clear or green glass bottles.
  • 3. Sourcing. You've probably got a few bottle-os in your neighbourhood where you usually buy beer. How do they store it? Are the refrigerated displays right by the windows, or up against a lighted glass door? That may not the best place to buy. Chances are, if the store sells varieties more exotic than Heineken, then the store's distributor takes the beer and its storage seriously. Visit a craft beer bar -- or, if you're feeling adventurous, head over to your favourite local brewery during tasting hours -- to ask a pro where to get the best beer around. As long as you can trace the darkest, coldest path the beer can take, you'll enjoy the freshest beer you can find.

Drinking Age

Even if heat and age don't cause skunkiness (in the absence of light), those factors can absolutely affect the flavour of your beer. When beer goes stale, it doesn't curdle or sour like a spoiled dairy product. This leads a lot of people to think that beer doesn't go bad. And it kind of doesn't. But age does take it further and further away from the flavour profile that the brewmaster intended, primarily due to oxidation.

This is where refrigeration is important. Beer starts getting stale (as in the flavours start changes) surprisingly fast. Like with eggs, meat, or dairy, keeping it cold will keep it fresher, longer. You may start to taste the flavour changes after as few as five days! That means if you're buying imported European beer -- which generally comes via sea, unrefrigerated -- in most cases it's stale before it gets to you. (Like you needed another reason to jump onto the American craft-beer bandwagon.)

So, despite what you learned freshman year of college, it has nothing to do with taking it out of the fridge and then re-cooling it. It's just time spent unrefrigerated, period. And, of course, even refrigerated beer will go stale. It'll just take longer. The responsible thing to do is drink it.


Take care of your beer. Pamper it a little. Respect its delicate chemistry, and make sure it's been treated tenderly. Raise a glass to brewmaster George di Piro, aka Professor Beer, who writes eloquently about the effects of oxidation and ageing in beer. Then, next time you're at a summer party, and a friend putting beer on ice starts pontificating about skunking, go ahead and punch him in the brain with your newly acquired knowledge.

Image credit: Shutterstock/ Ronald Sumners


    I don't think any Australian beer company sells their beer in clear bottles, and I don't know of any bottleshop that would import American beers unless their customers have been specificaly asking for it (and I don't think that any Australian who knows anything about beer would willingly drink the cheap, sold in clear bottles, brands that are being refered to in the article).

      Aussie beers come in clear glass, Hahn Ice and Carlton Cold spring to mind.
      And my local bottle shop sells Bud and Miller brands of American Beer to name two, I assume they are imported.

        To the extent that those can be called "beer", sure.

        There are tonnes of them!!!! Tooheys Extra Dry in addition to the ones greg named...

      @alphamohe. Have you ever been to a bottleo? As mentioned there are a heap of Aussie clear bottle beers and you can buy Millers and Bud from pretty much any generic bottle shop!

      Personally, I only drink what tastes good and generally that's craft beer

      Coopers clear, Fosters, some version of Tooheys, and several other brands do..

      Okay so Fosters isn't owned by an Australian company any more.. But I guess it counts.

      You can add Tooheys Extra Dry and Corona (which is brewed here) to that list, although I believe the reason TED comes in clear bottles is that the hops they use in it are not light sensitive or the cold-filtered brewing process removes the light sensitivity or something. There was a fuss made about it when it first hit the market.
      Now that MIllers owns CUB, you can expect more American beers to be brewed and sold here in the future.

      My local has plenty of american craft beers they import. Although it is a dan murphy's.

    Coopers Clear. Tooheys Extra Dry. And many more.

    Canned beer is mostly awful, it does taste metallic, and doesn't taste as good as it would from a keg.

      Keg beer is great. You can't go wrong with the good old xxxx tinnie mate. That's the beer of the Australian working mans economy. You want a job done around a work site, ask them how many cartons it will take

    Just a note that not all beers go "stale" quickly. If the beer is bottle conditioned (live yeast still in the bottle) then it can often improve with age (to a degree). This is even more valid for certain ales such as Stouts, Porters, Old Ales, etc.

    And sours are a different game altogether (often aged for 6-months to 3+ years)

    In India, Kingfisher comes in clear, amber and green bottles and the taste is noticeably different in clear bottles. My Indian colleagues thought I was being an idiot about it, so I told them to blind test me - put beer from a clear bottle and beer from coloured bottles into glasses and I'll tell them which is which. I was able to pick 6 from 6 but only from comparison. i.e. I couldn't have just had one taste and said which it was, but by tasting all 6 glasses I could pick the three that came from the clear bottle. Definitely one of my proudest beer moments.

    "it has nothing to do with taking it out of the fridge and then re-cooling it"

    I don't think this is true, especially for twist tops. Twist tops that have been re-cooled are easier to open, and always taste like shit. I'm no expert, but I always figured that the glass expanding and compressing from different temperatures would affect the seal, allowing more air to get in/escape/whatever air does to spoil the beer.

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