Common Wine Faults and How to Identify Them

Wine faults are specific, identifiable defects — chemical, microbial, or physical — that degrade a wine's aroma, flavor, or structure in ways that fall outside the winemaker's intention. Some faults are immediately obvious; others hide behind descriptors that sound almost complimentary until the context clicks. Knowing the difference between a flaw and a feature shapes every tasting experience, from a $15 bottle at a grocery store to a $150 wine at a restaurant.

Definition and scope

A wine fault is any sensory defect caused by a spoilage compound, a contamination event, or a production failure. The Court of Master Sommeliers and the Wine & Spirit Education Trust (WSET) both recognize a core set of faults that sommeliers are trained to detect — the most prevalent being cork taint, oxidation, volatile acidity, reduction, refermentation in bottle, and Brett (Brettanomyces contamination).

The scope matters here. A fault is not the same as a style preference. Some wine drinkers interpret mild Brettanomyces character — earthy, barnyard-like, leathery — as complexity. The distinction between fault and feature often depends on threshold: at low concentration, Brett can add intrigue; at high concentration, it overwhelms the fruit entirely. The same threshold logic applies to volatile acidity and reduction. What separates fault identification from personal preference is whether the defect compound has crossed above a recognizable sensory threshold.

For anyone building knowledge about the broader world of wine evaluation, Wine Faults and Defects is a useful companion to the wine tasting terminology page, where fault-adjacent descriptors are placed in full context.

How it works

Each major fault has a distinct chemical origin and a corresponding sensory signature:

  1. Cork taint (TCA) — Caused by 2,4,6-trichloroanisole (TCA), a compound formed when chlorine-based compounds react with naturally occurring molds in cork. Detection threshold for TCA in wine is roughly 1–5 parts per trillion (Cork Quality Council). Smells like wet cardboard, damp basement, or musty newspapers. Suppresses fruit character dramatically.

  2. Oxidation — Excessive exposure to oxygen degrades ethanol and fruit compounds. White wines turn from straw to amber; reds lose vibrancy and turn orange-brown at the rim. Aromas shift toward sherry, walnut, or flat apple juice. Oxidation is chemically inevitable over time — it becomes a fault when unintentional.

  3. Volatile acidity (VA) — Primarily acetic acid (vinegar) and ethyl acetate (nail polish remover). Produced by acetic acid bacteria. Low levels are legally permitted under TTB wine production standards (27 CFR § 4.21) — up to 1.2 g/L for red wine and 1.1 g/L for white. Above threshold, it registers as harsh, prickly, and acetone-like on the nose.

  4. Reduction — Hydrogen sulfide and mercaptans formed when yeast are stressed during fermentation. Smells like struck match, rubber, or rotten eggs. Notably, reduction is often correctable: 20–30 minutes of aeration, or decanting, can dissipate lighter mercaptans entirely.

  5. Brettanomyces (Brett) — A spoilage yeast producing 4-ethylphenol and 4-ethylguaiacol. Aromas include barnyard, band-aid, smoked meat, and horse stable. Common in red wines aged in previously used barrels with sanitation gaps.

  6. Refermentation in bottle — Residual sugar reactivated by yeast after bottling. Creates unwanted bubbles in a still wine, often with a yeasty or slightly sour edge.

Common scenarios

The restaurant test: A corked wine — TCA contamination — is the most common fault encountered at a restaurant table. Estimates from the Cork Quality Council place TCA-affected bottles at roughly 1–3% of all natural cork closures, though winery sanitation improvements have pushed that figure lower over the past two decades. If a wine smells muted and faintly musty compared to what the label suggests, the bottle warrants a respectful mention to the server.

The cellar discovery: A bottle opened after extended storage that smells strongly of vinegar has crossed into VA fault territory. This can happen when a cork seal failed over years, allowing slow oxygen infiltration and bacterial activity. Learning wine storage and cellaring fundamentals is the most direct prevention.

The natural wine confusion: Reduction and mild Brett appear with higher frequency in natural wines, where sulfite additions are minimal and cellar interventions are limited. The natural wine explained page covers this tension between fault tolerance and production philosophy directly.

Decision boundaries

The practical question is whether to return, aerate, or drink through a given wine. A simple framework:

Understanding the wine fermentation process and oak aging and wine provides the mechanistic background that makes fault identification less mysterious — because most faults trace back to a specific intervention point in production.

References

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