Understanding Wine Faults: How to Spot a Bad Bottle

What Is a Wine Fault?

A wine fault is a defect caused by winemaking errors, contamination, or storage problems that makes the wine unpleasant to drink. It is important to distinguish faults from stylistic preferences — a wine you simply do not enjoy is not faulty; a wine that smells like wet cardboard is.

The Major Wine Faults

Cork Taint (TCA)

What it is: Contamination by 2,4,6-trichloroanisole, a compound that forms when natural cork interacts with certain mold-produced compounds and chlorine.

How to spot it: The wine smells like wet cardboard, musty basement, or damp newspaper. At low levels, TCA may simply mute the wine's fruit aromas without adding an obviously off smell.

How common: Estimated to affect 3-5% of wines sealed with natural cork.

What to do: Return the bottle to the retailer or send it back at a restaurant. Cork taint is the most widely accepted reason for returning wine. This is not your fault — it is a manufacturing defect.

Oxidation

What it is: Excessive exposure to oxygen, causing the wine to deteriorate.

How to spot it: White wines turn deep gold or brown; red wines turn brick-brown. Aromas shift from fresh fruit to stale, bruised apple, or sherry-like (in a wine that should not taste like Sherry). Flavors become flat and lifeless.

Causes: Faulty cork, poor storage, or too much headspace in the bottle.

Note: Some wines are intentionally made in an oxidative style (Sherry, Vin Jaune, some orange wines). This is a stylistic choice, not a fault.

Reduction

What it is: The opposite of oxidation — the wine has been deprived of oxygen, producing sulfur compounds.

How to spot it: Aromas of struck match, rubber, rotten egg, or cooked cabbage. At mild levels, it can smell like flint or gunpowder.

What to do: Mild reduction often blows off with decanting or vigorous swirling. Severe reduction (mercaptan or hydrogen sulfide) is harder to resolve and may indicate a permanent fault.

Volatile Acidity (VA)

What it is: Excess acetic acid (vinegar) and its ester, ethyl acetate (nail polish remover).

How to spot it: The wine smells like vinegar or nail polish remover. At low levels, VA can add lift and complexity (especially in some natural wines). At high levels, it is unambiguously a fault.

Causes: Bacterial contamination during winemaking, often from acetic acid bacteria.

Brettanomyces (Brett)

What it is: A wild yeast that produces compounds with distinctive aromas.

How to spot it: Aromas of barnyard, horse blanket, band-aid, sweaty saddle, or smoky bacon. At very low levels, some tasters enjoy the complexity Brett adds (it is common in traditional Rhône, Bordeaux, and Barolo wines). At high levels, it overwhelms the wine's fruit.

The debate: Whether Brett is a fault or a feature is one of the most contentious topics in wine. Many traditional producers consider a touch of Brett to be part of their wine's identity.

Heat Damage (Cooked Wine)

What it is: Wine that has been exposed to excessive heat during storage or shipping.

How to spot it: The wine tastes stewed, jammy, and flat, with muted aromas. The cork may be pushed slightly out of the bottle. The capsule may show signs of seepage.

Causes: Poor storage — a car trunk in summer, an uninsulated warehouse, or shipping without temperature control.

Refermentation

What it is: Unintended second fermentation in the bottle, usually from residual sugar and viable yeast.

How to spot it: The wine is unexpectedly fizzy or spritzy when it should be still. May also appear slightly cloudy.

Note: A tiny bit of spritz in a young white wine is often intentional (Vinho Verde, some Muscadet). In a full-bodied red wine, it is usually a fault.

What to Do with a Faulty Bottle

At a Restaurant

• Politely tell your server you think the wine may be faulty
• Most reputable restaurants will replace it without argument
• You do not need to be an expert — just describe what you smell or taste

At a Retail Store

• Return the bottle (preferably with the cork and some wine remaining)
• Most good wine shops will exchange or refund without hassle
• They can then return the bottle to their supplier for credit

At Home

• If the wine is from an online purchase, contact the retailer
• Document the issue (photo of the label, vintage, and cork)
• Most reputable online retailers have return policies for faulty wines

Prevention

• Buy from reputable sources that store wine properly
• Check bottles before buying: Look for signs of seepage, pushed corks, or excessive sediment in young wines
• Store properly: Temperature control is the best insurance against faults
• Consider screwcap wines: They eliminate cork taint entirely

The Bottom Line

Most wine faults are obvious once you know what to look for. Trust your nose — if something smells genuinely unpleasant (not just unfamiliar), the wine may be faulty. And never feel embarrassed about sending back a corked or damaged bottle. It happens to every wine lover eventually.