Skunked Beer
December 15, 2009
As Scott continues his journey into the craft of home brewing for The Brew Club he will (unless he has a raging thirst) need to bottle his beer, which brings us quite nicely to the subject of ‘skunked beer‘.
Beer becomes ’skunked’ when it is unintentionally exposed to light; more specifically, to Ultra-Violet (UV) radiation which is most prevalent in sunlight and fluorescent light. Brown glass filters the most UV radiation, green less so, but the choice of which colour bottle to use depends on what type of beer you’re bottling.
The light sensitive chemicals are compounds derived from hops, which as you know are used in beer both as a preservative (traditionally in IPAs where the extra hop compounds allowed the ale to journey from England to India without spoiling) and as a flavouring – adding bitterness. It’s the bitterness compounds that are susceptible to skunking, rather than the aromatic oils. Which is why, despite the ‘hoppy’ nose of many fine lagers (such as Pilsner Urquell) there is less concentration of the bitterness compounds, which is why lagers tend to be bottled in green, or even clear glass bottles, and ales in brown.
Settle down… this is the science bit:
The actual chemicals, which could form up to 15% of the dry hop flowers are alpha-acids, these are transformed in the brewing process (by the addition of heat) into iso-alpha-acids and it is these that add the bitterness to a brew.
Subsequent addition of UV energy allows these acids to react with sulphur compounds in the ale (there are several hundred different chemical compounds inside a good ale) to form 3-methyl-2-butene-1-thiol (thiol indicates sulphur).
It is the sulphur in the 3-methyl-2-butene-1-thiol that shares the malodorous properties of stink bombs, well water and skunks – an offensive odour. Hence skunkiness, AKA ’skunked beer’.
And time is not a factor in this; research has shown that a well-hopped beer can become ‘lightstruck’ in less than a minute in bright sunlight – perhaps that’s why real ale pubs in Britain tend to be dingy!
Other than selecting a bottle that filters the UV light, then brewers can modify their brews to reduce the iso-alpha-acids (but retaining alpha-acids) – such as by dry-hopping – this adds the aromatic nature of the hops, but less bitterness.
And that is the story of skunked beer. Do you take precautions to keep your beer from getting skunked? Have any skunked beer stories to share, or add anything to the above post? Please share!
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December 15th, 2009 at 11:54 am
I was never exactly sure what skunked meant in taste terms (no skunks over here you see) so I did my own little test during the summer by leaving a bottle of Heineken in the sun for three days, with a control bottle in the fridge. Truly awful! I had thought to repeat the experiment with Jever Pils, but just couldn’t bring myself to do it
Barry M´s last blog ..Löwenbräu Triumphator
December 15th, 2009 at 12:15 pm
A braver man than me Barry, and no we don’t have many skunks in Essex!
Love the graphics Liz!
Bob the Brit´s last blog ..The Lord Mayor’s Show
December 15th, 2009 at 12:21 pm
Hey Bob,
Like Barry – I wasn’t too sure what skunked beer meant… except that it was yucky brewski… Thanks for the great info!
Also, thanks for the compliments on the drawings!
Glad you liked them!
Lis – SB Reports´s last blog ..From Championship to Sinking Ship… Presenting The 2009 Pittsburgh Steelers
December 15th, 2009 at 12:24 pm
Thanks for the science lesson Bob. I’ve never had the displeasure of smelling, let alone tasting skunked beer. However I am keeping my beer in the garage now that is lighted with florescent bulbs. I will take extra precaution to make sure my beer is in boxes or the fridge, especially the stuff in clear glass bottles. Thanks for saving my beer! You are a gentleman and a scholar.
-Don
Don´s last blog ..Ten Million Horses Can’t Be Wrong!
December 15th, 2009 at 5:57 pm
Yeah, Bob and Liz are good people! I’ve had a few skunkers over the years but I never really knew it was a process until much more recently. I’ve also read that some of the marketing behind putting lime in certain beers in clear bottles was that lime would mask any skunkiness to a degree. I also thought it funny that the Newcastle Brown Ale gets listed as a ‘possible related post’!
Scott-TheBrewClub´s last blog ..Home Brew Kits – The Final Review
December 15th, 2009 at 7:20 pm
Yeah I can’t say I’ve ever had a skunked beer and I’m hoping not to. But one thing I have noticed is that friends of mine not familiar with beer tend to just think beers that are very hoppy are skunky. They don’t know any better and it doesn’t taste like a major macro so they assume it’s skunked.
Mike – MikeLovesBeer.com´s last blog ..Bison Organic Gingerbread Ale
December 15th, 2009 at 11:19 pm
My precautions for avoiding skunked beers are primarily focused on not buying Heinekken. It can be refreshing and tasty, but it frequently has a skunky taste to it, especially when purchased in six packs, I suppose because they have less packaging to shield the green bottles from UV light. I dunno. But it’s amazing how many skunky Heinekken’s I’ve had!
Jim´s last blog ..Its a Butte CLARK!
December 21st, 2009 at 11:25 am
Thanks for the technical post, Bob. Like mike, I don’t ever recall having a skunky beer, so I’ve not thought about it to much. Glad to know the reason.
Simply Beer´s last blog ..Avery duganA Double IPA