Is This Bottle Bad? The Most Common Wine Faults, Explained

A faulty bottle is not your fault, and it is not rare. Roughly one in every twenty cork-sealed wines has cork taint. Oxidation happens to old bottles with compromised seals and to any bottle left open too long. Knowing the handful of real faults means you stop second-guessing yourself and start trusting your nose.

Cork taint: the wet-cardboard smell

This is the most common fault you will encounter. It smells like wet cardboard, musty basement, or newspaper left in the rain. The culprit is 2,4,6-trichloroanisole (TCA), a compound that forms when chlorine-based substances react with specific molds found on cork. TCA mutes the wine's fruitiness and leaves that characteristic damp, musty character behind.

Cork taint affects about 2 to 5 percent of wines sealed with natural cork. If you open a bottle and it smells like a wet dog, it is corked. Return it. Any reputable restaurant or shop will take it back, no questions asked. Tell the sommelier or server, "I think this might be corked." They should smell it, confirm, and bring you another bottle. Do not finish the glass hoping the smell will fade. It will not.

Screw caps and synthetic corks remove some risk of TCA. However it is still possible for the wine to be exposed to TCA before it leaves the winery.

Oxidation: bruised apple and a browning color

Oxidation happens when too much oxygen gets into the wine during production, storage, or after opening. Wine needs small amounts of oxygen as it ages, but too much exposure leaves it flat and tired. It smells like bruised apple, Sherry, vinegar, or stale brown sugar. White wines take on amber or brown tones; reds fade from vivid purple-red to brown at the edges.

If you open a fresh bottle and it smells oxidized, it is faulty. Return it. If it is an older bottle, check your storage conditions. If it is a bottle you opened two days ago and left on the counter, that is expected.

The exception: certain wines are made in an oxidative style on purpose. Sherry styles like Fino and Amontillado, Madeira, and Vin Jaune from the Jura are produced this way and should smell like this. Know what you bought.

Reduction: struck match, and the copper-coin trick

Reduction is the opposite problem. When a wine sees too little oxygen during fermentation or aging, sulfur compounds accumulate. The wine smells like struck match, rubber, onion, garlic, or cooked cabbage. Occasionally you will catch a whiff of rotten egg, which is hydrogen sulfide.

People often assume reduction means they got a bad bottle, but it usually affects every bottle from that production run. Natural wines are more prone to it. Swirl the wine hard in your glass or pour it into a wide container to expose it to air. With enough air, reduction typically fades within 20 to 30 minutes. If the smells persist, the wine is significantly reduced.

A sommelier trick: try placing a clean copper coin in the glass and giving it a swirl. The copper reacts with the sulfur compounds and can clear up mild reduction in moments.

Refermentation: fizz where there should be none

You ordered a still wine, and there are tiny bubbles. The wine smells slightly yeasty or vinegary and tastes off-dry when the label says dry. This is refermentation in the bottle. Leftover sugar and active yeast that survived bottling can restart fermentation inside the sealed bottle, producing CO₂ and sometimes volatile acidity.

You see this more often with natural wines and smaller producers who skip filtration or use minimal sulfur. If you ordered a still wine and it is fizzy, say something. Fans of pét-nat might not mind, but that depends on the style you ordered.

A few more worth recognizing

Volatile acidity smells like vinegar or nail polish remover. Bacteria produce acetic acid, which creates this sharp smell. Natural wines are more susceptible.

Brettanomyces (Brett) smells like barnyard, band-aid, leather, or horse. A wild yeast called Brettanomyces causes it. This one is controversial. Some producers and critics value it in small doses for the complexity it adds; high levels ruin the wine. More on this below.

Heat damage makes the wine smell like stewed fruit. It tastes flat, jammy, and lifeless. Poor storage or shipping in high heat causes this. The wine has essentially been cooked.

Light strike smells like onion or skunk, similar to skunky beer. UV light is the culprit, which is why you see this most often in white wines sold in clear glass bottles.

Brett: the fault people argue about

Brett gets its own section because it sparks real debate among wine professionals. In small amounts, Brett contributes leather, spice, and an extra layer of interest. Many classic Burgundy and Southern Rhône wines carry detectable Brett and are celebrated for it. When it dominates, the wine smells like a dirty stable, and that is not salvageable.

If you encounter a wine with subtle leathery, earthy complexity, that might be intentional. If it smells like a horse stable, it is a fault.

What is not a fault

Sediment in older red wines is normal and expected. Pour slowly and stop before the sediment reaches your glass.

Tartrate crystals are small deposits you might find on the cork or floating in a white wine. They are potassium bitartrate, completely harmless. Not a fault.

A slight spritz in Vinho Verde or Muscadet is intentional style, not refermentation.

Natural variation in color: certain orange wines are intentionally hazy.

When in doubt, send it back

A suspected fault is not something you should have to prove. If the wine smells wrong, say so. At any good restaurant, the sommelier or server should smell it, confirm or clarify, and act. Replacing a bottle is much cheaper than losing a guest's trust. The standard protocol: a good sommelier will smell the cork and taste a small amount before presenting the wine.

If the wine smells like wet cardboard, bruised apple, or a barnyard, you are not imagining it.

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