When the bottle is wrong: a practical guide to wine faults
Andi Healey
Web Manager
Hospitality trade • Wine service
When the bottle is wrong: a practical guide to wine faults
What each fault smells and tastes like, what causes it, and what to do when a guest finds one.
Wine faults fall into two categories: those that are immediately obvious and those that require some knowledge to identify. Both matter in a service context. A table that receives a flawed bottle and is not handled correctly leaves with a memory of the experience rather than the wine.
This guide covers the six most common faults: cork taint, oxidation, volatile acidity, Brettanomyces, reduction, and heat damage. For each: the cause, the sensory markers, the service response, and where the fault sits on the fixable-to-irreversible spectrum.
Quick-reference table
The table below gives the key information for each fault at a glance. The sections that follow cover each one in more detail, including what to do when a guest raises it at the table.
| Fault | Primary smell | Fixable? | Service response |
|---|---|---|---|
| Cork taint (TCA) | Wet cardboard, damp basement, mouldy newspaper | No | Replace without question |
| Oxidation | Sherry-like, stale, flat; nutty or caramelised on palate | No | Replace; check storage conditions |
| Volatile acidity | Vinegar; nail varnish remover at higher levels | No | Replace if clearly excessive; note that low VA is normal |
| Brettanomyces | Barnyard, leather, wet animal, medicinal | No; sometimes improvable with air | Context-dependent; replace if guest is dissatisfied |
| Reduction | Struck matches, rotten eggs, rubber, drains | Often yes, with aeration | Decant or aerate first; replace if it persists |
| Heat damage | Cooked fruit, caramel, flat | No | Replace; review storage and delivery chain |
Cork taint (TCA)
The most well-known fault and the one guests are most likely to name. TCA (2,4,6-trichloroanisole) forms when naturally occurring fungi in cork come into contact with chlorine-based compounds, typically from cleaning agents or wood preservatives used during production. At concentrations as low as a few parts per trillion, it is detectable by smell and suppresses the wine's aromatic character entirely.
Estimates vary, but typically 1-5% of wines sealed with natural cork are affected to some degree. The fault can also occur in wines sealed with screw caps or synthetic closures if TCA contamination entered at an earlier stage of production, though this is considerably less common.
How to identify it
The primary marker is a musty, damp smell: wet cardboard, mouldy newspaper, or a damp basement are the standard descriptors. On the palate, the wine tastes flat and stripped. The fruit character that should be present is suppressed rather than replaced by anything actively unpleasant, which is what makes mild cork taint difficult to identify with certainty. A wine that simply seems dull and lifeless, with no other obvious fault, may be lightly corked.
On guest confidence
A guest who identifies a wine as corked is almost always correct. The musty flatness of TCA is distinctive enough that it is rarely confused with anything else. Replacing the bottle without question is the right response. Arguing the point, even if there is genuine uncertainty, is not a recoverable position. If the replacement bottle from the same case shows the same fault, the issue is likely in the batch and the producer should be notified.
What to do
TCA cannot be corrected once it has affected a wine. The bottle should be replaced. Keep the original bottle and closure for return to the supplier. Reputable producers and distributors will accept returns on corked bottles without requiring significant justification.
Oxidation
Oxidation occurs when wine is exposed to more oxygen than intended, either during production, through a compromised closure, or as a result of improper storage. Oxygen reacts with the phenolic compounds in wine, forming acetaldehyde and other oxidative compounds that alter the wine's colour, aroma, and flavour.
A critical distinction: some wines are deliberately oxidative in style. Tawny Port, Oloroso Sherry, and certain traditional Chardonnays develop their character through controlled oxidation during ageing. The fault is unintentional oxidation in a wine that should not have those characteristics.
How to identify it
Colour is the first indicator. White wines shift from bright, clear hues toward amber or brown. Red wines take on a brick-red or tawny colour at the rim rather than their usual vibrant tones. On the nose, fresh fruit aromas are replaced by flat, stale, or sherry-like notes. The palate confirms the picture: the wine tastes dull, lacks acidity and freshness, and may show nutty or caramelised characteristics that do not belong there.
What to do
Oxidation cannot be reversed. A bottle that has oxidised due to a faulty closure or poor storage should be replaced. If oxidised bottles are appearing repeatedly from the same case, storage conditions should be reviewed: wine stored upright for extended periods, in warm environments, or subject to significant temperature fluctuation is at much higher risk. The issue may be in the cellar rather than the bottle.
Volatile acidity
Volatile acidity (VA) refers to acetic acid and its by-products, primarily ethyl acetate, which form when acetic acid bacteria convert alcohol into acetic acid in the presence of oxygen. All wine contains some level of VA: at low concentrations it is part of a wine's aromatic complexity. It becomes a fault when it exceeds the threshold at which it dominates the aroma and palate.
Brettanomyces activity, poor sanitation, inadequate sulphur dioxide management, and oxygen exposure during ageing or bottling are all contributing factors.
How to identify it
The primary marker is a sharp, vinegar-like aroma. At higher levels, ethyl acetate produces a nail varnish or paint-thinner note that is immediately apparent. On the palate, the wine tastes sharp and acidic in a way that overwhelms the other components, often with a burning sensation in the throat. High VA disrupts balance: even a wine with pleasant underlying fruit can be rendered unpleasant if the VA level is too high.
The calibration question
Sensitivity to VA varies significantly between individuals. Some drinkers detect it at very low concentrations; others are largely unaware of it until levels are high. Some traditional and natural wine styles carry measurable VA as part of their character. The relevant question for service purposes is not whether VA is present but whether it has reached a level that clearly detracts from the wine's intended profile.
What to do
Excessive VA cannot be corrected. If a guest raises it and the fault is clearly present, the bottle should be replaced. Low-level VA in a wine where some rustic character is expected is a matter of preference rather than fault. In those cases, the conversation is worth having before the bottle is opened if the guest's palate is known to be sensitive.
Brettanomyces
Brettanomyces (Brett) is a wild yeast that produces volatile phenols, primarily 4-ethylphenol and 4-ethylguaiacol, during fermentation or ageing. It is most commonly associated with red wines aged in oak barrels, where it can establish itself in crevices that are difficult to sanitise completely. Brett thrives in the presence of oxygen but survives in low-oxygen conditions too.
Brett is the most divisive fault in the wine trade. Some traditional wine regions and producers tolerate or actively court low levels of Brett for the earthy complexity it adds. Others treat any detectable Brett as a production failure. The correct position for service purposes is to understand the spectrum and know where each wine on your list is intended to sit.
How to identify it
The aromatic profile of Brett runs from barnyard and leather at lower concentrations through wet animal, sweat, and medicinal notes at higher ones. At very high levels it produces a hospital-like phenolic smell that obliterates fruit character entirely. On the palate, Brett can add an earthy, gamey quality at low levels; at high levels it creates bitterness and a metallic sensation that strips the wine of freshness.
What to do
Brett cannot be removed from a wine. Decanting and aeration may allow some of the volatile compounds to dissipate, improving the presentation marginally. It is worth attempting before replacing the bottle if the Brett level is moderate and the wine's other qualities are intact.
If a guest is dissatisfied, replace the bottle. The conversation around Brett is worth having proactively with guests who are ordering wines from producers or regions where Brett character is a known feature of the style. Framing it correctly before the bottle is opened avoids a fault conversation later.
Reduction
Reduction is the opposite condition to oxidation: it occurs when wine has had insufficient oxygen contact during production or ageing, leading to the accumulation of sulphur compounds, primarily hydrogen sulphide and mercaptans. It is more common in wines aged under reductive conditions, particularly in stainless steel, or sealed with screw caps, which provide a near-airtight environment.
Reduction is the one fault on this list that is frequently correctable in service. Many reduced wines respond well to aeration and arrive at the table in a state that the guest never needs to notice.
How to identify it
The aromatic range runs from struck matches and burnt rubber at mild levels through to rotten eggs, garlic, drains, and cabbage at more severe levels. Hydrogen sulphide produces the rotten egg note; mercaptans produce the garlic and rubber notes. On the palate, the wine may taste flat or show a metallic bitterness. The key diagnostic test is aeration: if the off-aromas dissipate with vigorous swirling or decanting, the wine is reduced rather than otherwise faulty.
The copper trick
A clean copper coin dropped briefly into a glass of mildly reduced wine can bind with hydrogen sulphide and neutralise the rotten egg note. It is not a service solution and should not be used at the table, but it is a useful diagnostic tool when assessing a bottle before service. If the off-aroma clears with copper contact but not with aeration alone, the fault is reduction rather than something more serious.
What to do
Decant or aerate first. Mild reduction typically resolves within a few minutes of oxygen contact. If the off-aromas persist after thorough aeration, the reduction is severe enough that the wine is unlikely to recover fully. In that case, replace the bottle. Worth noting: some recently released wines, particularly from producers using minimal sulphur and reductive winemaking, benefit from decanting as standard practice rather than as a fault remedy.
Heat damage
Heat damage occurs when wine is exposed to excessive temperature, either during storage or transit, accelerating the chemical reactions that cause ageing. The name maderisation comes from Madeira, a wine style that undergoes controlled heat treatment as part of its production. In all other contexts, it describes an unintentional fault.
Wine left in a warm delivery vehicle, stored in a poorly ventilated cellar, or subjected to significant temperature fluctuation is at risk. The damage is cumulative: repeated short exposures to high temperatures can be as damaging as a single extended one.
How to identify it
Colour is often the first signal. Whites shift toward amber or brown; reds develop a brick or tawny tone at the rim earlier than their age would suggest. The nose shows cooked or stewed fruit, caramel, and a flat, muted quality where freshness and primary aromatics should be. On the palate, the wine may taste overly sweet, syrupy, or simply dull, lacking the acidity and definition that should be present.
Heat damage produces a wine that has aged prematurely and without the complexity that proper bottle age develops. The result is a wine that tastes old without tasting interesting.
What to do
Heat damage cannot be reversed. Replace the bottle and review the delivery and storage chain. If multiple bottles from the same case are showing the same characteristics, the issue is likely in transit or storage rather than in an individual bottle. Document the fault with photographs and notify the supplier. Most reputable distributors will credit heat-damaged stock if the evidence is clear.
A fault handled well is not remembered as a fault. It is remembered as a service that took the guest seriously.
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