Everything You Ever Wanted to Know About Cork Taint

Mosaic of corks on blue/green background
Illustration by Julia Lea

Ever sit down, pour yourself a glass of wine and have it smell reminiscent of a wet newspaper or moldy basement? Or swirled a glass of wine and noticed it smelled muted, or like nothing at all? If so, chances are your wine was cork tainted, or more commonly, “corked.”

Cork taint is a contaminant in wine caused by musty aroma compounds. The most common culprit is 2,4,6-trichloroanisole (TCA). While some wine flaws, such as brettanomyces and volatile acidity, can be subjective as to whether they hurt or enhance a wine, cork taint is universally considered a flaw at any detectable level.

The cause of cork taint

TCA is formed in tree bark when fungi, mold or certain bacteria come into contact with a group of fungicides and insecticides, collectively referred to as halophenols. These were widely used during the 1950–1980s and remain in the soil. Fungi have a defense mechanism that chemically alters these compounds, rendering them harmless to the organism but creating TCA in the process.

Many producers make cork for their wine closures out of tree bark and, unfortunately, they don’t always know if parts of the bark were contaminated with fungicides or insecticides. If they were, their resulting corks would damage any wine they touch.

Cork oak and piles of cork oak barks in Los Alcornocales Natural Park, Cadiz, Andalusia, Spain
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This is the most common way wines become TCA tainted, although others do exist, like barrel, equipment or winery contamination. It is possible, though rare, for screwcap wines to be cork tainted if they come in contact with this contaminated equipment.

TCA can also occur when sodium hypochlorite (bleach) reacts with lignin, a naturally occurring wood compound. This creates a compound called 2,4,6-trichlorophenol (TCP). Mold, yeast and bacteria then convert this compound into TCA.

Descriptions of cork taint date back to the early 20th century. However, it wasn’t until 1981 that TCA was identified as the main cause of cork taint in wine by the Swiss scientist Hans Tanner and his research team.

Humans have a remarkable sensitivity to cork taint, with people able to smell TCA between two and five parts per trillion, and some even below one part. That’s like being able to identify one teaspoon of water from 1,000 Olympic-sized swimming pools.

Wine Faults and How to Recognize Them

The effects of cork taint

Cork taint inhibits olfactory signal transduction, creating a muting effect. Simply put, it interferes with your ability to smell. Heavy cork taint gives off an unpleasant aroma reminiscent of a musty basement. In lesser amounts, however, TCA can simply blunt aromas and flavors, making a wine seem muted and uninteresting. Recent research indicates that TCA itself has no smell, but it appears to suppress olfaction in such a way that presents as dull or moldy odors.

Some researchers believe humans are sensitive to cork taint because TCA’s musty smell is similar to mold in food, which could potentially be harmful to us. However, TCA itself has no harmful effect on humans, other than ruining your wine. You can safely drink or cook with cork-tainted wine, it just won’t taste as pleasant.

TCA is quite stable over time, whereas other aroma compounds are not. This means cork taint can become more prominent as a wine opens up or as a bottle ages. It also means cork-tainted bottles may not show obvious fault. It can make wines seem like they’re just not very good, when in fact they were contaminated.

Close up of glasses of wine on a table during a wine tasting
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The pervasiveness of TCA in wine

In blind tastings for Wine Enthusiast, between 3.5–6% of the wines sampled by this author appeared to be contaminated by TCA or another musty aroma compound (“appeared” because the presence of TCA was not confirmed by testing). With 30 billion bottles of wines produced per year closed by cork, this equates to an estimated one billion bottles ruined by TCA annually.

The Cork Quality Council states that 3% of the corks it tests are contaminated by TCA. If you are drinking one bottle of wine per day, assuming they are all closed with natural corks, you would expect to have 7–22 corked bottles of wine per year.

There is a misconception that wines are more likely to be cork tainted if they are less expensive. The line of thought is that cheaper wine uses less expensive, and therefore inferior quality, cork. However, corked bottles of wine can be found at $9, $120 or beyond. The average price of a TCA tainted bottle of wine sampled from Washington last year was $43.

How to detect cork taint

Until the day when all natural corks can be reliably and individually tested for TCA and other musty compounds, winemakers and drinkers will have to contend with cork taint. The best thing you can do as a consumer is learn how to reliably recognize it.

The best way is to start by smelling the wet end of the cork every time you open a bottle. Look for a faint or strong musty aroma. Then smell the wine and look for the same. The more you practice detecting cork taint, the more sensitive you will become to it. Soon you will start to perceive more subtle contaminations.

Should You Smell the Cork When Opening Wine? Always.

Wine fault kits that include TCA can also be purchased. Keep in mind, however, that these will have a very strong presentation.

You may have had cork-tainted wine and not even noticed. Individual sensitivity to cork taint varies quite widely, with some people able to smell TCA below one part per trillion and others unable to smell it at 200 times that amount. These differences are largely believed to be genetic, although training can help increase sensitivity. However, the taint can still affect your enjoyment of a wine, even if you are not aware of its presence.

Individual perception can also vary. One day you might be able to smell cork taint at two parts per trillion. Another day, you might struggle to identify it at five. Sometimes you might smell a glass and get a whiff of it, but when you try to get it again, you can’t. This is because the cork taint itself inhibits olfaction.

In some styles and varieties, like many white wines and Pinot Noir, TCA can be detected at lower levels. Other varieties, like Cabernet Sauvignon, can require significantly higher levels of TCA for it to be noticed, due to the variety’s often powerful aromatics, which can increase with oak aging.

However, many people use the term “corked” to signify anything that is wrong with a bottle of wine, at times even for wines they just don’t like. This is incorrect. The term should truly be used only for bottles that have a musty presentation.

Even wine professionals trained to identify TCA contamination can miss mild cases. In such instances, the wine does not obviously present as cork tainted, but rather seems muted and disappointing.

Assortment of wine bottle corks seen from above
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How to prevent cork taint

Winemakers utilize a variety of techniques to try and minimize the presence of cork taint. This can include soaking a selection of corks from each bale in a neutral alcohol solution and then smelling each to look for TCA. If they find a contaminated cork in a sampling, they reject the entire bale.

Some cork suppliers have also recently started testing individual corks for the presence of TCA. This, of course, adds to the cost.

Unfortunately, there is very little consumers can do on this front. Once a wine is contaminated by TCA, it will remain so. TCA contamination has nothing to do with storage conditions like temperature, humidity or holding a wine too long.

What if I buy cork-tainted wine?

If you purchase a bottle of wine and detect TCA contamination, there unfortunately isn’t a fix. Certain tricks, like using Saran Wrap or a teaspoon of heavy cream, can sometimes lessen the impact of TCA, but they also significantly impact many other attributes of the wine.

Instead, you might want to bring it back to the retailer or winery where you bought it. They will typically replace the wine free of charge so long as you have your receipt.

The Pros & Cons of Different Wine Closures

This is true for restaurants as well. Though sending back a wine you suspect is contaminated might feel awkward, a professional staff will graciously handle a polite request for a new bottle. If the provider doesn’t replace a corked wine, consider taking your business elsewhere in the future.

Unfortunately, for people who collect wine or buy wine when they travel, certain bottles are irreplaceable.

Thankfully, over the long term, cork taint is declining. In the late 2000s, TCA taint was said to be substantially higher than it is now, perhaps as much as 9.5% of wines. However, over the past five years, the percentage of corked wines has seemed to remain consistent.

Beyond the glass

TCA might seem like a wine-centric problem, but bagged, store-bought baby carrots often show high levels of TCA contamination. This is because the carrots are soaked in a dilute bleach solution, which can contribute to the production of trichloroanisole. There are anecdotal reports that baby carrots have in some cases desensitized people to smelling TCA and/or finding it distasteful.

TCA can also affect other produce that is stored or transported in wood crates or cardboard boxes, like apples. TCA has even been noted in freeze-dried pasta.

Published on August 20, 2020
Topics: Wine Basics