Skunked Beer

Skunked beer: how to avoid a drink that stinks

Most of the time, for most people, enjoying a beer is a simple and uncomplicated pleasure. But sadly we don’t live in a perfect world – things can and do go wrong even with a beautiful beer. Life can be cruel, don’t you think?

Let’s be real though. For the most part the various off-flavours in beer are subtle and hard to spot, and plenty of people drink plenty of beer that’s supposedly ‘off’ and have a great time doing it.

There is one type of off-flavour that drinkers seem to care about more than all the others put together though, and that is skunking. Perhaps because it’s more common, or more noticeable – or perhaps just because there’s more written about it online so people are more aware of it. (Ironic.)

Despite all this concern, skunked beer remains a subject that lots of people have heard about only vaguely, and one they probably don’t quite understand. So here’s an explanation that should put that right.

What is skunking?

Some beers are described as ‘dank’. They have a weed-like smell because of the hops they were brewed with. (Hops are related to cannabis, in case you didn’t know.) That’s not what I’m talking about here. I’m talking about when something has gone wrong with the beer and it’s displaying a character other than that intended by the brewer.

Beer doesn’t go off. Not really. But there are a number of ways in which it can go… crap. Oxidation can make lagers taste like cardboard. Poorly controlled fermentation can make ales smell like nail-polish remover. And some beers get skunky. That is, they have an unpleasant, sulphuric smell just like a skunk’s distinctive spray.

How can I tell if my beer is skunked?

Sniff it and see. The first sign is the smell. You really can’t mistake it once you’ve encountered it a couple of times. The taste is a give-away too, so if you’re still not sure give it a sip and hold it in your mouth for a little while, then pay attention to the flavour.

What does skunked beer taste like?

It tastes pretty much like it smells. Imagine a beer with an offensive, sulphuric, all-pervasive taste of… ick. There’s a slightly manky, wet-dog aspect to it. And in really bad examples it’s just like the other kind of skunk.

Is it caused by letting cold beer get warm?

In a word, no. The sort of temperature changes you’re likely to put a beer through in everyday life are not going to have much of any effect on it. But that’s beside the point. The point is beer temperature change has nothing to do with it. Skunking is 100% not caused by cycling the temperature of your beer from cold to warm or vice versa.

How does it happen?

A quick note for my fellow Europeans, who probably haven’t ever smelled a skunk: this off-flavour is also called light-strike, which anyway is a much more useful term because it not only describes what’s wrong with your beer but why it’s gone wrong in the first place.

Skunking, or light-strike, is an off-flavour in beer caused by a chemical reaction between hop flavour compounds in your beer and ultraviolet light.

This is probably as much as your average drinker needs to know: it’s the light, dumbass. But if you do want to get all nerdy about it check out the section near the bottom of this post for further details. For the rest of us though let’s move on to some more immediate concerns.

Is it safe to drink skunked beer?

Yes, drinking a skunked beer is perfectly safe. It’s just a little less pleasant than it ought to be. You know, because of the skunking.

Can you get sick from drinking skunked beer?

No. Or no more sick than you might get from drinking any beer, if you have too much. When it comes to health concerns, there’s nothing different about skunked beer compared to normal beer that has not been skunked.

Is skunked beer still alcoholic?

Absolutely. The alcohol content of a beer remains completely unchanged by the light-strike reaction. It’s the hop-derived iso-alpha-acids that are affected when a beer becomes skunked, not the alcohol. The beer is the same strength and its ABV remains unchanged.

Is there a list of skunky beers?

Well… that’s a tough one. There is no definitive list. Almost any beer can be affected by light-strike under the right conditions. (Or perhaps that should be ‘the wrong conditions’.) What I can tell you is that if your beer is hoppy, and if your beer is exposed to light, then your been can become skunked. The more hops a beer contains the more susceptible to skunking it is. Both natural and artificial light can skunk a beer.

Skunking happens fast – within seconds – so the longer your beer has been exposed to light the more likely it is to become light-struck. If your beer has been stored in a clear, green, or blue glass bottle that means it’s been exposed to light for some time before you even open it. That’s why beers in these colour bottles are more likely to taste skunky right away. But all beer is exposed to light once it’s poured into your glass, so any beer can become skunked as long as it contains hops. Which, you know, most do these days.*

Try it yourself: create a skunked beer at home

Worried that I might be talking bullshit? Concerned you might not recognise the light-struck aroma when you next encounter it? Relax! Here’s a good way to kill those two birds with one simple stone.

Get yourself a beer. Preferably something good and hoppy, and that comes in a can so it can’t be skunked already. Pour half the beer into a glass and leave it in direct sunlight for a while – 15 to 30 minutes should do the trick. Keep the rest of your beer somewhere dark during this time. Back in the fridge is ideal – but remember temperature has nothing to do with it. Then it’s a simple matter of tasting both side by side to compare and contrast. You should notice a difference.

Can you deskunk a beer?

Nope. You’re shit out of luck there, pal.

What to do with skunked beer

Asking for the same beer again in these circumstances is a mug’s game.

If you’ve been served a beer in a pub that’s already light-struck then you’re within your rights to ask for another. But before you do, stop to think about why that beer has been served skunked in the first place.

This won’t happen to beers served from a can, a keg, or a cask. Those are all opaque so the beer inside can’t be light-struck. You’ve probably just ordered something that comes out of a glass bottle that isn’t brown. If it’s already skunked when it arrives that’s a sign of incorrect storage.

Asking for the same beer again in these circumstances is a mug’s game. The replacement will most likely be skunked too. What you should do is send it back and ask to have something else instead – and this time go for something on tap or in a brown bottle.

If the person serving you won’t accept the return, or can’t tell that the beer has been skunked when you point it out, make plans to drink elsewhere in the future. This is clearly not an establishment that values good beer and good service.

Most of the time returning your beer is no longer an option by the time you discover that it’s skunked. Then you only have two options left: drink it anyway or throw it away.

Silver lining: just keep sniffing

I’m going to suggest you keep that skunked beer you probably paid good money for, and what’s more you drink it too. But not right away. Sniff it a bit more first. That’s right, get a good snoutful of that skunky smell and then go back and do it again.

Our noses are very sensitive to the smell of skunked beer. As a result our olfactory system quickly becomes desensitised to it. (Imagine if it didn’t – we’d be overloaded, a twitched mess on the floor begging for the smell to stop.) If you keep on honking down that light-strike aroma you’ll soon stop noticing it at all. At which point, you can get on with enjoying your beer. There’s nothing really wrong with it after all.

Nerd-out time: the details behind light-strike

It’s the light, dumbass.

Hops contain alpha acids and beta acids. When hops are boiled – as happens during the normal brewing process – the alpha acids are isomerised and become iso-alpha acids, or more speficially isohumulones.

Skunked beer is the result of a photochemical reaction of isohumulones with light at certain wavelengths. This reaction produces a chemical called 3-methyl-2-butene-1-thiol, or 3MBT for short. This is a mercaptan – which means it’s well manky. 3MBT is chemically very similar to a skunk’s spray.

What sort of light produces skunked beer?

Beer is affected by light which is between 400 and 500 nanometers (nm) in wavelength (the blue end of the spectrum), and ultraviolet light, which has a wavelength below 400nm.

Fluorescent tube lighting emits the worst kind of light for skunking: “Most of the photons that are released […] have wavelengths in the ultraviolet (UV) region of the spectrum, predominantly at wavelengths of 253.7 and 185 nanometers.”

How does glass protect beer from light?

Here’s how various colours of glass commonly used in beer bottles stands up to the photon onslaught:

Brown glass blocks out light under 500nm – which is basically everything that we’re worried about. Yay, brown glass!

Green glass only blocks out light under 400nm. In other words, it’s not that effective. Boo, green glass!

Clear glass? Forget about it. That shit’s not blocking anything at all. Get outta here, clear glass!

‘But hang about bruv,’ I hear you say. ‘I had a beer from a clear glass and that shit wasn’t skunked.’ Yes – that’s possible. To get around light-strike some of the large macro brewers don’t use hops as we normal folk understand them. Instead they use tetra-hops. This is a hop extract which has light-resistant isomerised alpha acids. This is basically an inert form of hops that will not react when exposed to light, UV or otherwise.

What about cans?

Cans block out all light and therefore are ace. Duh.

Sensitivity to light-strike

A single drop of food colouring in 18 million gallons of water.

Humans get a bad rep when it comes to our sense of taste and smell compared to other members of the animal kingdom. But let me tell you, we’re not so bad when it comes to sulphuric compounds. Our sensitivity to these extends to one part per trillion (ppt).

That ?? is ?? crazy ??.

It’s kind of hard to get your head around just how tiny one ppt is. One part per trillion is equivalent to one nanogram per kilogram, or a single second out of 32,000 years. To get an idea, one ppt would be represented by a single drop of food colouring in 18 million gallons of water, or traveling 6 inches out of a 93 million-mile journey toward the sun.

This matters because it doesn’t take long to produce one ppt of 3MBT in beer, and it doesn’t take much for us to notice it.

Some further reading

If you want to delve even deeper into the subject of light-strike a.k.a. skunked beer, take a look at these: I got mad links, yo.

A conclusion at last

Well done for making it this far. This is where I’ve kept the boiled down wisdom you’ve been looking for. The best way to avoid skunked or light-struck beer is to be careful about the beer you buy. If it’s not in a brown bottle or a can, then be wary about where it has been stored and for how long. If it’s in a green bottle near a sunny shop window perhaps choose something else instead. If it’s a dusty bottle that’s been sat for who knows how long underneath a strip light, don’t expect it to taste great. And once you’ve bought it, look after you beer. Keep it in the dark. It’s happy in the dark. Like a goth.


* The first recorded use of hops in beer was in 822 CE.

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