Craft beer column: Why leaving your pint out in the sunshine makes it stink like a skunk

Brewin' Up A Storm column with beer experts Susan and Judith Boyle from Kildare

Craft beer column: Why leaving your pint out in the sunshine makes it stink like a skunk

Sunshine can harm your pint!

The recent extended sunshine spell got us thinking and questioning — what is all this sun doing to your beer?

Have you ever been out in a beer garden with a lovely pint of cool, refreshing beer, only to be 10 minutes into your pint when the flavour changes and your drink is just not nice anymore?

Most people think this is just because your pint has warmed up (which is a factor), but what is actually happening is that the molecules in your beverage are changing.

Just like your skin, your beer reacts to the UV light found in the sun’s rays. This effect is usually stopped by what your beer has been packaged in, be that a can or a brown bottle. When drinking a pint in a clear glass, all the UV rays hit the beer and react, creating an unpleasant taste and order which is commonly referred to as ‘skunked’ or ‘light struck’.

This makes your lovely, fresh-smelling hoppy beer smell like cooked cabbage, rotten eggs or — as the name suggests — the smell a skunk lets off when you scare it.

This reaction also happens to white wine or champagne if left outside in the sunshine for too long, so it is not just beer drinkers that get a shock half way through their drink.

In beer, it is the hops iso-acid humlone that breaks down and changes to form methlybut-2-ene-1- thiol-3 which creates this new distinctive smell and taste.

The ‘thiol’ at the end of the very long chemical name indicates that there is now sulphur present, and this is what gives the beer the rotten egg, cabbage smell and taste.

However, as with all off-flavours in beer, people have different tolerances to the smell and flavour.

Some people are very sensitive to light strike, while others can hardly pick it up.

What might make it even more confusing is some beer brands want this flavour in their beer.

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It has become a signature of some beers that either use a water that has a high sulphur content to brew, or that do not think that it is worth their while protecting their beer from the sun during packaging as they believe it will be exposed to UV rays at some stage during the production or drinking process.

But for some beer brands, the idea of this happening to their beer is almost criminal.

A case in point is Sierra Nevada, who started packaging their highly hopped beers in cans to keep them as fresh as possible and protect the beer from UV rays.

They only ship their beer in cold storage and ask distributors in each of the countries they export to to keep their beers cold throughout the delivery process.

This ensures that the consumer gets the freshest beer possible and the beer taste as the brewer wanted.

Heat can also be a problem in beer, but to a lesser extent as most beer has a quick turnaround time.

Heat will quicken up the oxidation process, so if a beer is kept in warm conditions for extended periods of time it will go stale quicker than if it was refrigerated.

But unless oxygen got in to the beer during packaging, this process will take a relatively long time to become noticeable to the consumer.

Therefore, during this heat wave it is the sun that is your beer’s worst enemy.

So next time you are having a beer out in the sunshine, don’t forget to keep your beer shaded and cool to keep it nice and refreshing till the end of your pint.

Judith Boyle is a qualified chemist (MSc) and accredited beer sommelier. Susan Boyle is a playwright, artist and drinks consultant. See Both sisters are proud to be fifth-generation publicans. Their family business is Boyle’s bar and off-licence in Kildare town

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