What are wine faults?

Wine faults are the reason sommeliers sniff every bottle before pouring. They are unintended off-flavours that range from mildly distracting to pour-it-down-the-sink awful. Here is your field guide to the main culprits.

Cork taint (TCA) is the most infamous. It makes wine smell like wet cardboard, damp basement, or musty newspaper. It is caused by 2,4,6-trichloroanisole, a chemical formed when natural cork comes into contact with chlorine compounds. About 2-5% of cork-sealed bottles are affected. The perception threshold is insanely low -- just 2-4 parts per trillion.

Oxidation happens when wine gets too much air exposure, either through a faulty closure or during winemaking. Whites turn brownish and taste like bruised apples or stale nuts. Reds lose their vibrancy and develop sherry-like notes. A little oxygen is essential for ageing; too much is fatal.

Volatile acidity (VA) is essentially vinegar. Small amounts add lift and complexity; above 0.7 g/L for whites or 0.9 g/L for reds, it becomes a fault. You will notice a sharp, vinegary smell and a nail-polish-remover note from ethyl acetate.

Brettanomyces (brett) is a wild yeast that produces barnyard, horse sweat, and medicinal aromas. Some wine lovers actually enjoy low levels of brett for the 'rusticity' it adds, especially in southern French and traditional Barolo wines. Others consider any brett a dealbreaker.

Lightstrike is a fault you might not expect: UV light causes riboflavin in wine to break down, creating unpleasant cabbage and wet-wool aromas. It is most common in clear glass bottles, especially Champagne and Sauvignon Blanc. This is why serious producers use dark glass.

The best way to learn faults? Smell them intentionally. Wine fault aroma kits and workshops (like those at 20hVin in La Hulpe) let you experience each fault in a controlled setting, so you can spot them in the wild.