Glossary
Oxidation
Reaction with oxygen, producing wet-cardboard and sherry notes in pale beer and dried-fruit depth in strong dark beer.
Also called oxidised, oxidized, cardboard, wet cardboard, trans-2-nonenal.
The full record
Oxidation has its own catalogue entry with the detail this page summarises — causes, thresholds, related styles and evidence.
Oxidation — The universal ageing fault: oxygen degrades beer into papery, cardboard-like staleness, and dulls everything that made it good.
The cardboard note is largely trans-2-nonenal, formed from lipid precursors and detectable at very low concentrations. Sherry and port character comes from a different set of reactions and is the same phenomenon presenting agreeably.
That dual nature is why oxidation cannot simply be listed as a fault. In a fresh pilsner it is a defect; in a five-year-old barley wine it is much of what the drinker was waiting for.
Related
More vocabulary
Acetaldehyde · Autolysis · Bottle bomb · Diacetyl · DMS · Gushing · Lightstrike · Staling
See every term on the glossary index.
Last reviewed 2026-08-16.