Oxidation

What it tastes and smells like

• wet cardboard
• paper
• stale sherry
• toffee in dark beer
• dulled hop aroma

Responsible compound: trans-2-nonenal and related carbonyls.

Styles this tends to affect

Not where it belongs — where it is most likely to appear when something has gone wrong.

• Alcohol-free pale lager — A pale lager produced at or near zero alcohol, now the largest and most refined part of the no-alcohol category.
• Altbier — Düsseldorf’s copper-coloured hybrid: ale-fermented and cold-conditioned, with firm bitterness over nutty, toasty malt.
• American amber ale — Caramel malt depth meeting American citrus hops — the maltier counterpart to American pale ale.
• American IPA — The defining modern craft beer: intense citrus, tropical and resinous hop aroma over a lean malt base, finishing firmly bitter.
• American lager — A very light, highly attenuated pale lager brewed with a substantial proportion of maize or rice, prioritising drinkability and cold service.
• American pale ale — The beer that defined American craft brewing: clean pale malt under bright citrus and pine hop character, balanced rather than extreme.
• Belgian pale ale — An everyday Belgian ale, toasty and biscuity, with restrained yeast character compared with the stronger Belgian styles.
• Best bitter — A step up from ordinary bitter in strength and depth, with more malt body while staying firmly sessionable.
• Bière de Garde — A malty, rounded French farmhouse ale brewed for keeping — richer and less peppery than its Belgian saison cousin.
• British strong ale — A broad category of strong English ales, malt-led and fruity, sitting between strong bitter and barley wine.
• Czech amber lager — A Bohemian amber lager balancing caramel malt against Saaz hop character, sitting between the pale and dark Czech beers.
• Czech pale lager — The Czech everyday lager: lower in strength than the premium version but keeping the soft bready malt and generous Saaz hopping.
• Czech premium pale lager — The original pale lager: rich bready malt, generous Saaz hopping and a rounded bitterness that soft Bohemian water makes possible.
• Dark mild — A low-strength dark British ale, gently sweet and nutty, built for drinking in quantity after physical work.
• Double IPA — IPA scaled up: more strength, more hops and more bitterness, while staying dry enough to remain drinkable.
• Dry stout — Sharp roasted-barley bitterness over a light body and a very dry finish — much lighter to drink than its colour suggests.
• English brown ale — A malt-led brown ale with hazelnut and caramel character, moderate strength and a dry, clean finish.
• English IPA — The original IPA: a strong, firmly bitter English pale ale with earthy, floral hop character and a dry, mineral finish.
• English pale ale — The bottled British pale ale tradition: biscuity malt, earthy and floral English hops, and a firm, dry, mineral finish.
• English porter — The original dark British beer: chocolate and light coffee over a nutty malt base, restrained rather than aggressive.
• Foreign extra stout — A strong export stout, more intense in roast and body than a dry stout, historically brewed to travel.
• International amber lager — A light, commercially-produced amber lager, most familiar in its Mexican form, with gentle caramel over a crisp body.
• International dark lager — A commercially-produced dark lager, light in body and gently sweet, with colour contributing more than flavour.
• International pale lager — The global mainstream lager: pale, clean, lightly hopped and built for consistency and refreshment above flavour intensity.
• Irish extra stout — A stronger, fuller dry stout with more malt depth and body while keeping the sharp roasted-barley character.
• Irish red ale — An easy-drinking malt-led ale with caramel sweetness and a distinctive dry, faintly roasty finish.
• Kellerbier — Unfiltered, gently carbonated lager served young from the cellar, with a soft yeasty fullness filtration removes.
• Kölsch — Cologne’s pale hybrid beer: ale-fermented then lagered, giving lager clarity and crispness with a whisper of fruit.
• London brown ale — A low-strength, notably sweet dark brown ale from London, now largely extinct as a commercial style.
• Low-alcohol bitter — A genuinely fermented British ale brewed at very low strength, keeping cask character without dealcoholisation.
• New England IPA — Hazy, soft and intensely aromatic: tropical and stone fruit hop character with deliberately low bitterness and a full, juicy body.
• Ordinary bitter — The everyday British cask ale: low in strength, gently bitter, and built to be drunk in pints over a whole evening.
• Red IPA — An IPA built on caramel and amber malt, where toffee depth sits underneath full American hop character.
• Scottish ale — Malt-forward Scottish ales with caramel depth and very restrained hopping, traditionally graded by shilling price.
• Session IPA — IPA hop intensity at a strength you can drink several of — lean, dry and aromatic, with the malt kept minimal.
• Strong bitter — The strongest of the bitters, with pronounced malt richness, firm bitterness and noticeable fruit from warm fermentation.
• West Coast IPA — The dry, clear, aggressively bitter interpretation of American IPA, built on pine and grapefruit with the malt stripped right back.

If you are drinking it

If a beer tastes of wet cardboard or paper, or simply of much less than it should, it is stale. It is not unsafe — just past its best. A retailer will usually replace beer sold well past its date. Buy hop-forward beer fresh and keep everything in the fridge.

• Store beer cold and dark, and drink hop-forward styles as close to packaging as possible. Check the date on the can before buying. (prevents)
• Nothing recovers an oxidised beer. Once the cardboard note is present it cannot be reversed. (cannot be reversed)

Not a safety issue. Beer’s alcohol, hop compounds and low pH make it inhospitable to organisms that cause illness.

What causes it

If you are brewing it

• Brewer: Purge vessels and packaging with CO₂, transfer under pressure without splashing, and measure total package oxygen rather than assuming it is low. (prevents)

Where in the process this comes from

Steps that can produce this fault when they go wrong. Each links to what the step is for and how it is controlled.

• Barrel ageing — Mature beer in wooden barrels for the wood and spirit character they contribute, or for the microflora they harbour and the slow oxygen exchange they allow.
• Cask breather — Admit carbon dioxide at atmospheric pressure to replace beer drawn from a cask, instead of letting air in.
• Cask conditioning — Complete fermentation and carbonation inside the cask the beer will be served from, so it arrives at the drinker alive.
• Dry hopping — Add hops to beer after fermentation, without heat, to extract aroma compounds while adding essentially no bitterness.
• Forced ageing test — Hold packaged beer warm for a fixed period to accelerate staling, predicting in days how it will taste after months on a shelf.
• Packaging — Move finished beer into its final container with as little oxygen pickup as possible, because oxygen taken up here determines how the beer ages.
• Sensory panel — Assess beer against its own specification using trained tasters, screened and calibrated against known spiked standards.

Often confused with

• Faded hop character — loss of hop aroma, dull, muted character

Questions