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

Today’s off-flavour is oxidation. This one is all about old beer or beer that has been mishandled. When oxygen sneaks into beer, it reacts with compounds in the malt and hops, creating stale flavours.

What does it taste like? The classic descriptors are cardboard, paper, or wet paper, sometimes even stale sherry in darker beers. Hop character fades, malt sweetness turns dull, and the beer feels lifeless. In pale hoppy beers like IPAs, oxidation can be brutal — turning vibrant citrus hops into a sweet, sticky mess.

Oxidation usually happens when beer is stored for too long, exposed to heat, or packaged poorly. Once oxygen gets in, there’s no turning back. That’s why breweries are so careful about packaging under CO₂ and why fresh beer always tastes better.

Training your palate? Compare an old bottle of beer that’s been sitting around for a year with a fresh one. That stale cardboard character is oxidation in a nutshell.

So if your pint tastes like wet cardboard, it’s not the pub’s fault — it’s oxidation.

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