A defect (or fault) is an undesirable characteristic that detracts from a wine's quality, caused by flawed grapes, winemaking or storage. Common defects include cork taint (musty TCA), oxidation, excessive volatile acidity (vinegar), reduction (rotten-egg sulfur), Brettanomyces (barnyard) and heat damage. Some, in trace amounts, are debated as complexity; in clear excess, all are flaws that mar the wine.
WHY IT MATTERS FOR COLLECTORS
Recognising defects protects your cellar and your money. A corked or heat-damaged bottle is a loss, not a style; knowing the signs lets you reject faulty wine at the table or on arrival.
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