Corked Wine: Identify and Oxidised Faults

You can identify corked wine by its distinct musty, mouldy aroma. That aroma is often described as "wet cardboard" or "damp basement," and it suppresses fruit characteristics. Oxidised wine, in contrast, shows a dulling of aroma. It evolves into notes of "cardboard," "straw," "hay-like," or even "sherry-like" and "madeirised" characters, particularly in white wines. Both faults diminish the wine's intended profile, but they stem from different chemical processes. 2,4,6-trichloroanisole (TCA) from the closure primarily causes cork taint. Oxidation results from excessive oxygen exposure, leading to compounds like acetaldehyde. Recognising these sensory cues helps you decide whether to open, hold, or consider the implications for your collection.

How do you identify cork taint?

Cork taint, also known as a "corky" wine, is a wine fault characterised by undesirable smells or tastes. Those smells are often described as "musty," "mouldy," "earthy," or "mushroom,". The primary compound responsible for cork taint is 2,4,6-trichloroanisole (TCA). It is one of the most odour-intense compounds known, according to AWRI: wine faults and taints. Some tasters at the AWRI can detect TCA at concentrations less than 1 ng/L. A study by Duerr (1985) determined the aroma threshold of TCA in a Pinot Noir wine as 1.4 ng/L. That threshold might be lower in dry white wines and higher in full-bodied red wines, according to AWRI: wine faults and taints. Prescott et al. (2005) reported a consumer rejection threshold for TCA of 3.1 ng/L, with a consumer detection threshold of 2.1 ng/L. The AWRI has observed TCA at a concentration as low as 1 ng/L. At that level it suppressed the ratings for overall aroma intensity and positive fruit-derived characters in a Semillon wine during sensory evaluation.

TCA is generally formed when moulds growing on cork come into contact with trichlorophenol, according to AWRI: wine faults and taints. Trichlorophenol can arise from aerial contamination or the chlorination of phenol, a natural component of cork. These moulds can detoxify trichlorophenol by adding a methyl group to form TCA. TCA is the most prevalent cause, accounting for an estimated 80-85% of all cork taints. Other odour-intense compounds can also impart musty, earthy, or mouldy aromas. These include 2-methylisoborneol (camphor-like, earthy, threshold 30 ng/L), geosmin (earthy, muddy, threshold 25 ng/L), and 2-methoxy-3,5-dimethylpyrazine (fungal must, threshold 2.1 ng/L in neutral white wine), as detailed by AWRI: wine faults and taints.

The cork industry group APCOR cites a study showing a 0.7-1.2% taint rate. A 2005 study of 2800 bottles tasted at Wine Spectator facilities found 7% of bottles to be tainted. TCA can also originate from sources other than cork, such as oak, as shown by the AWRI. This can lead to systemic TCA. The compound then infiltrates a winery through barrels, drain pipes, wooden beams, or rubber hoses, potentially affecting an entire production.

Can you remove TCA from a corked wine?

If you encounter a corked wine, one method of removing TCA is to soak polyethylene in the affected wine. The non-polar TCA molecule has a high affinity for polyethylene, which draws out the taint. You can do this at home by pouring the wine into a bowl with a sheet of polyethylene plastic wrap. The process is effective within a few minutes. Understanding the condition of your bottles, including potential fault risks, is crucial for managing your collection. You can learn more about assessing these risks in our guide on wine ullage levels explained.

What are the signs of oxidation in wine?

Oxidation in wine presents with sensory characteristics ranging from a dulling of the aroma to "cardboard," "straw," and "hay-like" aromas, according to AWRI: wine faults and taints. From there it progresses to "sherry-like" and "madeirised" notes. In extreme cases, aromas described as "wet wool," "wet dog," or "varnish-like" can be evident. Certain wine styles, such as sherry, encourage oxidation deliberately. In table wines it is generally considered a fault. The flavour of oxidation is due to multiple compounds, including a range of aldehydes, according to AWRI: wine faults and taints. Acetaldehyde is a key contributor, with a sensory threshold ranging from 100-125 mg/L. Above 125 mg/L, acetaldehyde can impart odours described as "over-ripe bruised apples," "stuck ferment" character, or "sherry" and "nut-like" characters. Acetaldehyde levels increase as wines age due to the chemical oxidation of ethanol.

Another significant sign of oxidation is volatile acidity (VA), generally perceived as the odour of vinegar, according to AWRI: wine faults and taints. The aroma threshold for acetic acid, the major component of VA, can be as low as 0.1-0.125 g/L, depending on the wine style and individual. However, the concentration at which it is considered detrimental is usually greater than 0.7 g/L. The legal maximum content of volatile acidity in Australian wines, excluding SO2 and expressed as acetic acid, is 1.5 g/L. Increased levels of acetic acid in stored wines are usually attributable to the growth of acetic acid bacteria. Those bacteria convert alcohol to acetic acid in the presence of oxygen.

Ethyl acetate, perceived as the odour of nail polish remover, can also contribute to the sensory perception of volatile acidity, according to AWRI: wine faults and taints. Its reported sensory threshold is 12 mg/L. Low levels (30-60 mg/L in "normal" wines) can contribute fruity aroma properties. Concentrations of about 150-200 mg/L are found in defective wines. Yeast and acetic acid bacteria produce ethyl acetate, and its formation is related to dissolved oxygen levels.

White wines, particularly those from "floral" varieties such as Riesling, are very prone to oxidation, according to AWRI: wine faults and taints. Red wines can withstand significant oxidation due to their higher content of phenolic compounds. Those compounds act as natural antioxidants. Effective sulfur dioxide management, refrigeration, and inert gas blanketing during production and packaging have made oxidation less common today. Proper storage conditions are paramount to mitigating oxidation risk. For more on maintaining ideal conditions for your collection, explore our guide on how to store wine.

How do closures and storage conditions affect wine faults?

Your choice of closure and your storage conditions significantly affect the risk of faults like oxidation and cork taint. A study by Chanut et al. (2023) demonstrated that the glass-cork interface is a major pathway for oxygen entry into bottled wines. This transfer at the interface accounts for more than 30% of the total oxygen transfer in cork stoppers without model wine. With model wine present, it accounts for nearly 70% of the total oxygen transfer after three months of storage at 20°C.

The study on microagglomerated cork stoppers found that the intrinsic oxygen barrier properties of the cork stopper alone remained unchanged over a 24-month period. That held regardless of the presence of model wine, storage position, or temperature, according to Chanut et al. (2023). However, the presence of model wine modified the total oxygen transfer, which includes the glass-cork interface. The total diffusion coefficient increased from 2.3 × 10−11 to 4.7 × 10−11 m2 s−1 after the initial three months of storage at 20°C with model wine. This increase is attributed to the sorption of water and ethanol in the cork. That sorption can plasticise the material and decrease the force applied to the glass, which promotes oxygen transfer at the interface.

Regarding storage position, Chanut et al. (2023) tested bottles standing vertically (cork in contact with vapour phase) and lying horizontally (cork in contact with liquid phase). Position had no significant influence on oxygen transfer through the cork or at the glass-cork interface over 24 months at 20°C. This finding aligns with some literature, though other studies have shown divergent results, as noted by Lopes et al. (2006) and Venturi et al. (2017).

Temperature, however, has a strong impact on oxygen transfer. Barrier properties remained unchanged over 24 months at 20°C. A storage temperature of 35°C led to a significant increase in total oxygen diffusion after 9 months, from 5.2 × 10−11 to 3.5 × 10−8 m2 s−1, according to Chanut et al. (2023). That increase came from higher transfer at the glass-stopper interface. At 50°C, a tremendous oxygen transfer was noticeable within the first 3 months. Values approached the diffusion coefficient of oxygen in air after 6 months, indicating leakage at the glass-cork interface. This is potentially due to the partial melting of the paraffin and silicone coating on the cork stopper, which has melting peaks around 45°C and 64°C.

What else in the cellar raises fault risk?

Beyond oxygen ingress, other environmental factors play a role in wine preservation:

• Humidity: Cork enclosures need some humidity to keep from drying out. A dry cork could allow oxygen to enter the bottle, leading to spoilage or oxidation. However, excessive humidity can damage labels, affecting resale value. Jancis Robinson notes that 75% humidity is often cited as ideal. Significant research to definitively establish an optimal range is limited.
• Light: Direct sunlight or incandescent light can adversely react with phenolic compounds, creating "wine faults." Light-bodied white wines are most vulnerable, and they often come in tinted bottles for protection.
• Temperature Swings: Rapid or frequent temperature variations cause corks to expand and contract, potentially introducing oxygen. Constant temperatures between 10 and 15°C (50 and 59°F) are generally recommended for long-term storage. Lower temperatures slow a wine's development.
• Vibration: Anecdotal evidence suggests vibration contributes to accelerated ageing with adverse effects. A study concluded that vibrations should be minimised to store red wines with limited changes in physicochemical properties.

Different closure types offer varying oxygen barrier properties, as noted by Crouvisier-Urion et al. (2018). Natural cork remains the favourite on aesthetic grounds. Screw caps win praise for consistency and reducing oxidation. Synthetic corks and screw caps are thought to be prone to sulphidisation. That may arise from reduced oxygen supply concentrating sulphurous smells.

Knowing which closure a bottle carries, and how much oxygen that closure lets through, is one more input to help you assess fault risk.

What other common wine faults should you know?

Beyond cork taint and oxidation, several other faults can affect fine wines, each with distinct sensory characteristics and origins. Recognising these helps you understand the condition of your holdings.

• Brettanomyces faults: Often referred to as "Brett," these faults come from the yeast Dekkera/Brettanomyces. The volatile phenol 4-ethylphenol imparts "Band aid®," "medicinal," or "pharmaceutical" characters, with an aroma threshold of 368 µg/L in a neutral red wine, according to AWRI: wine faults and taints. Other compounds include 4-ethylguaiacol, described as "clove," "spicy," or "smoky" (threshold 158 µg/L), and 4-ethylcatechol, which has a "horsey" aroma (threshold 774 µg/L). The sensory perception threshold for 4-ethylphenol depends on the wine style and structure. Full-bodied red wines, or those with significant oak influence, carry higher thresholds.
• Reductive wine faults: These arise from volatile sulfur compounds. Hydrogen sulfide (H2S), or "rotten egg gas," has a detection threshold of 1-2 µg/L in wine, according to AWRI: wine faults and taints. Unwanted sulfhydryls, also known as thiols or mercaptans, produce aromas like "cabbage," "garlic," "onion," and "rubber." Ethyl mercaptan has an "onion-like" and "rubber-like" aroma (threshold 1.1 µg/L). Methyl mercaptan is described as "rotten eggs" and "cabbage" (threshold 0.02-2.0 µg/L). Disulfides, such as dimethyldisulfide (DMDS) and diethyldisulfide (DEDS), can form from sulfhydryls and have aromas of "onions," "cooked cabbage" (DMDS, threshold 29 µg/L), and "burnt rubber," "garlic" (DEDS, threshold 4.3 µg/L). Dimethyl sulfide (DMS), formed during bottle maturation, can contribute "vegy" or "blackcurrant" character at low concentrations. At higher levels (threshold 30-60 µg/L), it presents as "asparagus," "cooked corn," or "molasses."
• Mousiness: This off-flavour is reminiscent of caged mice or cracker biscuit, according to AWRI: wine faults and taints. It generally shows late on the palate or after swallowing, and it can linger. It is rarely detected by sniffing. The compounds involved, primarily 2-acetyltetrahydropyridine (ACTPY), are not volatile at wine pH. Mousiness is usually of microbial origin, often from lactic acid bacteria. It is more likely in wines with low SO2 concentrations and low acidity.
• Additive-related faults:
• Sulfur dioxide (SO2): While a crucial preservative, excessive free SO2 can impart a pungent, penetrating aroma that causes sneezing and a choking sensation. A content of free sulfur dioxide up to 15 mg/L has no adverse sensory effect. Higher levels can be life-threatening to a small proportion of asthmatics, according to AWRI: wine faults and taints.
• Diacetyl: Produced by yeast and bacteria, diacetyl can add "buttery" or "butterscotch" characters at low levels (1-4 mg/L). However, at high levels (>5 mg/L), the aroma might be considered objectionable, making the wine defective.
• Geranium: 2-ethoxyhexa-3,5-diene causes this aroma, which is reminiscent of crushed geranium leaves. Lactic acid bacteria form the compound from the metabolism of sorbic acid. With an odour detection threshold of <1 ng/L, this compound is extremely potent and practically impossible to remove.

Understanding these faults is essential for evaluating your wines, whether you are considering their drink windows or assessing their value on the market.

How does our data help you assess fault risk?

Our platform provides comprehensive data to help you assess the condition and fault risk of your fine wine collection. We track key indicators that can reveal potential issues before they impact value or enjoyment.

For example, our condition scores help you understand how factors like ullage levels or label integrity might correlate with market performance. This insight is critical when deciding whether to hold a bottle for further ageing or to consider selling it.

We also analyse auction results, which can inform your buying decisions, particularly when considering wines with different closure types and their associated risks of faults like cork taint or oxidation.

Furthermore, our drink windows, combined with condition assessments, help you identify if a wine is approaching or past its optimal drinking period, where faults might become more pronounced.

By leveraging these insights, you can make informed decisions about your collection, from assessing individual bottles to understanding broader market trends. Our all-in cost calculator can also help you factor in potential risks and costs associated with wine faults.

Assess the condition and fill levels of your bottles to proactively manage your collection. Our condition and fill guide provides detailed insights to help you protect your investment.