Wine Faults Explained: How to Spot Cork Taint, Oxidation, Heat Damage and More

You raise the glass, take a sniff and something feels off. Is the wine meant to taste like that, or has it gone wrong? Most bottles you open will be perfectly sound, but every wine lover eventually meets a faulty one. Knowing the most common wine faults helps you judge a bottle with confidence, send one back politely in a restaurant, and store your own wines so that it happens less often.

Cork taint: the “wet cardboard” wine

The best-known fault is cork taint, usually caused by a compound called 2,4,6-trichloroanisole (TCA). It forms when moulds react with chlorine-based compounds, most often in natural cork but sometimes in barrels or winery timber. A “corked” wine smells of damp cardboard, a musty cellar or wet newspaper. Our noses are remarkably sensitive to TCA – many people can detect it at just a few parts per trillion – and even when the musty note is faint, it flattens the fruit, leaving a wine that seems dull and short.

Note that a corked wine has nothing to do with bits of cork floating in the glass. Those crumbs are harmless; simply fish them out.

Oxidation: when too much air gets in

Oxygen in small doses helps a wine develop, but too much turns it tired. Oxidised white wines darken towards gold or brown and smell of bruised apple; reds lose their bright colour, turning brick-orange, and taste flat and nutty. A failing cork, a bottle stored upright for years, or a wine left open too long are the usual culprits. Keep in mind that some styles, such as Sherry and Tawny Port, are made with deliberate oxidative ageing – in them, nutty notes are part of the character, not a flaw.

Heat damage: a real risk in tropical climates

For readers in Vietnam and across Southeast Asia, this is the fault to watch most closely. Wine exposed to high temperatures – a hot shop window, a car boot in the afternoon sun, a container sitting on a sunny dock – can become “cooked”. The fruit tastes stewed or jammy, the freshness disappears, and the wine feels lifeless. Warning signs on the bottle include a cork pushed slightly out of the neck or sticky wine residue under the capsule, both caused by the liquid expanding in the heat.

Where daytime temperatures regularly climb above 30°C, the simplest protection is to store bottles in a wine fridge or the coolest, darkest corner of the home, and never leave wine in a parked car.

Other faults worth knowing

Reduction

The opposite of oxidation: sulfur compounds that form when a wine has had too little oxygen. Think rotten egg, struck match or cooked cabbage. Mild reduction often fades with vigorous swirling or decanting; strong reduction does not.

Volatile acidity (VA)

Every wine contains a little acetic acid, and a touch can add lift. In excess, it smells of vinegar or, together with ethyl acetate, of nail-polish remover.

Brettanomyces (“Brett”)

A wild yeast that produces aromas described as barnyard, leather, sticking plaster or smoky clove. Brett is one of the most debated faults: some drinkers enjoy a hint of it in rustic reds, while others reject it at any level.

Light strike

Delicate whites and sparkling wines in clear or pale glass can be damaged by strong light. Ultraviolet and blue light trigger reactions involving riboflavin and amino acids, creating sulfur aromas of cooked cabbage or wet wool. The French call it goût de lumière – “taste of light”.

Not faults: crystals and sediment

Small, glassy crystals on the cork or at the bottom of a white wine are tartrate crystals, sometimes nicknamed “wine diamonds”. They form naturally when wine is chilled and are harmless. Dark sediment in an older red is equally natural – stand the bottle upright for a day and decant it gently.

What to do in a restaurant

When a sommelier pours you a small taste before serving the table, the ritual exists to check for faults, not to ask whether you like the wine. Look, swirl, sniff. If you suspect a problem, say so calmly – “I think this might be corked, could you take a look?” A good sommelier will taste it and, if the wine is faulty, replace it. Sending back a sound wine simply because it is not to your taste is a different matter, so it helps to know the difference.

📖 Glossary

• TCA (2,4,6-trichloroanisole): the main compound behind cork taint.
• Oxidation: deterioration from excess oxygen; browning and bruised-apple aromas.
• Reduction: sulfur aromas from a lack of oxygen.
• Volatile acidity (VA): vinegar-like acidity from acetic acid.
• Brett: short for Brettanomyces, a yeast giving barnyard or plaster aromas.
• Goût de lumière: light-strike fault in wines exposed to strong light.
• Tartrate crystals: harmless natural crystals, not a fault.

Learning to recognise faults is not about becoming a fussy drinker. It is about understanding what a healthy wine should be, so that every glass you pour – or send back – is a confident choice.

Please enjoy responsibly. Never drink and drive. Intended for adults of legal drinking age.

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