Welcome to The Certified Beer Nerd with Nigel Ayling — your guide to the geeky side of beer.

Today’s fault is lightstruck flavour, often just called “skunky.”

This happens when beer, especially in clear or green glass bottles, is exposed to sunlight or UV light. The light interacts with hop compounds to create 3-methyl-2-butene-1-thiol — the same chemical found in a skunk’s spray. And yes, it smells just as pungent.

You’ll pick it up as skunk spray, burnt rubber, or musty weed-like aromas. Even a few minutes in direct sunlight can cause it — that’s why “clear bottle lagers” have such a reputation.

Sensory training here is easy: grab a green-bottle beer, put it in the sun for ten minutes, and then open it. One sniff, and you’ll never forget it.

So if your beer smells like a skunk walked across the bar, you’ve found lightstruck character.

That’s The Certified Beer Nerd — levelling up your tasting skills, one sip at a time.