Beer faults

A green-apple note indicating beer served before fermentation finished — the classic sign of a rushed product.

Vinegar character produced by acetic acid bacteria, which need oxygen — so it always points to air ingress.

A drying, tannic harshness from over-extracted grain husk — the classic sign of sparging too hot, too long or at too high a pH.

A cheesy, sweaty aroma from badly stored hops whose beta acids have oxidised.

A temperature-dependent haze from protein and polyphenol binding — cosmetic only, and by definition it clears as the beer warms.

A medicinal, sticking-plaster note formed when chlorine meets phenols — almost always a cleaning or water-treatment failure.

A buttery compound with a very low threshold — normally a sign of rushed fermentation, but traditional at trace levels in some Czech lagers.

Beer spoiled between keg and glass by microbial growth in the lines — a venue problem rather than a brewery one.

A cooked-vegetable note from a malt precursor that a vigorous open boil should have driven off.

Sulphur compounds from fermentation — normal and transient in young lager, a fault when they persist.

The specific staling of hop character: the aroma fades first, and badly stored hops can turn cheesy.

Harsh, solvent-like alcohol heat from fermentation run too warm or under stress — distinct from the pleasant warmth of a strong beer.

A green, grassy note from extended contact with dry hops or from hops dried badly at harvest.

Beer that erupts on opening, caused either by refermentation in the package or by fungal proteins from mould-affected barley.

Unintended microbial growth — which is a fault only because it was unintended, since the same organisms define lambic.

Light breaks down hop compounds into a thiol chemically close to skunk spray — the fastest fault in beer, and entirely preventable.

A coin-like metallic note, usually from corroded equipment or high-iron brewing water.

An unpleasant taint of mixed-fermentation beer, characteristically tasted rather than smelled and arriving late on the finish.

Too much dissolved CO₂, from over-priming, incomplete fermentation before packaging, or contamination.

The universal ageing fault: oxygen degrades beer into papery, cardboard-like staleness, and dulls everything that made it good.

Cloudiness that does not clear with warming, usually from incomplete starch conversion or irreversible protein complexes.

Foam that collapses immediately — most often caused by grease or detergent residue in the glass rather than by the beer.

A soapy note from fatty acids released by yeast left too long on the trub, or from detergent residue in glassware.

A solvent-like ester that reads as pear drop at low levels and as nail varnish remover at high ones.

Fermentation stopping well short of terminal gravity — leaving a sweet, underdeveloped beer and a package-pressure risk.

Too little dissolved CO₂, leaving the beer flat and dull — carbonation carries aroma as well as providing texture.

Lactic sourness in a style that should not have it — a fault of intent rather than of the organism responsible.

Beer that finishes sweeter than intended, from under-attenuation, excess crystal malt, or a mash run too warm.

Cooked-vegetable notes that are not DMS — a residual category rather than a single compound.

Dead yeast breaking down and releasing rubbery, meaty compounds — the result of leaving beer too long on a yeast bed.