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There's A Scientific Reason Why Bottled Beer Sometimes Smells Like Weed

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There's A Scientific Reason Why Bottled Beer Sometimes Smells Like Weed

Have you ever cracked open a cold beer on a warm day and raised it to your lips, only to be met with a strange smell that reminds you of someone smoking a spliff?

Well, it's not just you - there is an actual scientific reason behind it.

It turns out that some beer turns 'skunky' - that's the term most people tend to use - because of a little-known chemical reaction that takes place in the bottle when the golden liquid reacts with the light of the sun.

Back in 2001, a group of scientists led by University of North Carolina professor of chemistry Malcolm Forbes PhD found the reaction takes place when beer containing hops is left in the sun.

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He's even suggested that this is one of the reasons that Corona - the beer, not that one - is served with a lime.

Let's hope these haven't been left in the sunshine. Credit: PA
Let's hope these haven't been left in the sunshine. Credit: PA

"Corona is marketed extremely cleverly," he posited.

Anyway, here's the science.

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Publishing their findings in Chemistry: A European Journal, Forbes and his team found that flavour compounds known as iso-alpha acids are brought forth when the beer is brewed.

That's what gives beer the distinctive - and frankly incredible - taste.

However, when those compounds are over-exposed to sunlight, they are turned into free radicals - atoms or molecules that have unpaired electrons - and that makes them highly reactive.

Those free radicals mix with protein and form another happy molecule called 3-methyl-2-butene-1-thiol.

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This catchy little fella makes a smell that is extremely potent, and smells like the spray of a skunk and - apparently - cannabis.

It's so strong that even one part per billion can be picked up by the human nose.

Hopefully, Professor Forbes can explain it better than that.

Keep 'em dark, and keep 'em cold. Credit: PA
Keep 'em dark, and keep 'em cold. Credit: PA
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He said: "Hops help flavour beer, inhibit bacterial growth, and are largely responsible for the stability of the foam in the head.

"Hops, however, are light-sensitive, and the three main compounds in them identified as being light-sensitive are called isohumulones [the iso-alpha acids].

"When attacked by either visible or ultraviolet light, these break down to make reactive intermediates known as free radicals that lead to the offensive taste and skunky odour."

To counteract this, most beer bottles are made brown or green to combat this process, but that doesn't mean they won't turn if left in the sun for too long.

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So, keep the beer inside and keep it in the dark. That's the best way to ensure this doesn't happen.

Oh, and keep it cold. No scientific reason, it just usually tastes better that way.

Featured Image Credit: PA

Topics: Science, Interesting, Food And Drink, Alcohol, Beer

Tom Wood
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