The practical takeaway is that a wine fault is a problem that makes a wine less sound, less typical, or less enjoyable. Some faults are obvious, like vinegar or wet cardboard. Others are matters of degree. A trace of earthy funk may add complexity to one wine and ruin another. Learning faults is less about memorizing scary words and more about recognizing when something blocks fruit, freshness, or balance.
TCA is the classic “cork taint” compound. A wine affected by TCA often smells like damp cardboard, wet basement, moldy newspaper, or muted fruit. The wine may not smell aggressively bad; it may simply seem dull and lifeless. TCA is associated with cork closures but can also come from contaminated winery materials. If a newly opened bottle smells musty and the fruit seems flattened, cork taint is a likely suspect.
Oxidation happens when wine is exposed to too much oxygen. In small, controlled amounts, oxygen can help shape wine during aging. In excess, it makes wine taste tired. Whites may turn darker gold or brown and show bruised apple, stale nuts, cider, or sherry-like notes. Reds may lose fresh fruit and become flat, pruney, or brown-edged. Some wines, such as Sherry, Madeira, and certain Jura styles, are intentionally oxidative; the key is whether the character fits the wine.
Reduction is almost the opposite problem: sulfur compounds develop in low-oxygen conditions. Mild reduction can smell like struck match, flint, smoke, or rubber, and some modern white wines intentionally carry a little matchstick character. More severe reduction can smell like rotten egg, sewage, onion, or burnt rubber. Swirling or decanting can reduce mild cases, but severe reduction may not blow off.
Brettanomyces, often shortened to Brett, is a yeast that can produce aromas such as barnyard, horse blanket, leather, clove, smoke, or medicinal Band-Aid. At low levels, some drinkers perceive it as savory complexity, especially in certain rustic red wines. At high levels, it can dominate the wine, dry out the fruit, and make different bottles taste the same. Whether Brett is a fault is partly cultural and partly a question of intensity.
Volatile acidity refers mainly to acetic acid and ethyl acetate. A little lift can make a wine smell more aromatic. Too much smells like vinegar, nail polish remover, or solvent. High VA can occur in dry wines, sweet wines, and wines made from damaged fruit. Some styles tolerate more VA than others, but when it burns the nose or overtakes fruit, it is a defect.
Other problems include mousiness, geranium taint, heat damage, lightstrike, refermentation, and microbial spoilage. Heat-damaged wine may smell cooked, jammy, or stewed and may leak around the cork. Lightstruck wine can smell skunky or cabbage-like, especially delicate wines exposed to strong light in clear glass. Unintended bubbles in a still wine may indicate refermentation, though some young wines retain harmless dissolved carbon dioxide.
The hardest part is distinguishing fault from style. A Fino Sherry should smell yeasty and saline. Madeira should taste oxidative. Traditional-method sparkling wine may smell like bread dough. A Syrah may have pepper, smoke, and meat notes without being faulty. Natural wines may show haze or wild aromas without being spoiled. The question is whether the note is integrated, expected, and balanced.
When assessing a possible fault, use a clean glass, smell the wine without overthinking, then taste. Ask whether fruit is present, whether acidity feels sound, whether the aroma improves with air, and whether the problem becomes more obvious over time. If a restaurant bottle smells clearly corked, oxidized, or otherwise defective, it is reasonable to ask for a second opinion. Fault knowledge should make wine less intimidating, not more punitive.