Wine faults are undesirable conditions that reduce a wine’s quality, clarity, aroma, flavor, or stability. They may arise from microbial activity, oxidation, reduction, heat damage, poor storage, unclean equipment, contaminated closures, or imbalanced chemistry, making fault recognition an important part of wine evaluation.
Common examples include cork taint, volatile acidity, oxidation, reduction, brettanomyces, mousiness, refermentation, lightstrike, and excess sulfur compounds. Some compounds are tolerated at low levels or even considered stylistic in certain contexts, but a true wine fault disrupts balance and obscures the intended character of the wine.