A Little Known Fact - Corked Spirits

While people know that corkiness exists in wine, many think it’s not possible for the same fault to occur in Spirits.

Admittedly, the incidence of cork tainted spirits is lower than wine – possibly because spirits’ higher alcoholic strength and aromatic intensity make it more difficult to pick up. But it does happen and manifests itself in the same way – a smell of wet newspaper or cardboard, a stale mustiness.

What is Cork Taint? 

The main culprit is a chemical compound called 2,4,6-trichloroanisole (TCA to its friends), which can be picked up at two parts per trillion (ppt) in the case of white wine. The level rises to 5ppt with red wines, and we can assume it would be higher again in the case of oak-aged spirits.

The trouble is that not everyone is highly sensitive to TCA and, while everyone can notice infection at 100ppt, only 50% of tasters (including experts) can pick it up at 10ppt. In other words, a lot of TCA-infected beverages are never noticed. 

TCA is produced when the phenols contained in wood (the tree bark used to manufacture corks, for example) are changed to TCP (2,4,6-trichorophenol) by chlorine, and then into TCA by microscopic fungi, in the presence of moisture.

It could exist in the bark of the tree if it has been treated by a chlorine-based fungicide, or emerge during the manufacture of the cork, particularly in the cork bleaching process.

There is an ongoing debate as to whether composite corks – the ones with lots of bits of cork stuck together – show a higher incidence of TCA. Results are inconclusive.

TCA isn’t just contained in cork, however. It can lurk in packing materials, wooden pallets, wooden shipping containers, cardboard boxes and casks. In fact, any damp, porous material which has been treated with a chlorine-based cleaning product can harbour TCA – even shower curtains. All can infect a cork.

TCP can also be produced by exposure to polychlorinated phenols used to treat wood. Every cask in one rum producer’s cellar had to be destroyed as a result of TCP infection.

In the wine industry, new batches of corks are sometimes tested through sensory analysis for TCA. Corks are taken, and each placed in a jar containing a neutral white wine. The following day, these samples are decanted into glasses, alongside one more glass of wine that hadn’t had cork in it, as control. Glasses and, if one showed TCA, then the batch of corks would be rejected.

Interestingly, although batches may be clean, samples sometimes show some flattening or diminution of aroma – one reason why so many fresh, light white wines are now routinely screw capped.

The wine industry has also moved away from chlorine-based cleaning products, while the cork industry has introduced new technology to try to eliminate TCA taint (chlorine is no longer used by major cork firms, such as Amorim). This, plus the move away from cork and into screw caps, has reduced the incidence of TCA taint dramatically.

Spirits, on the other hand, especially Craft Spirits, is moving the other way and corks are now increasingly commonplace. As a result, it is inevitable that TCA infection will have risen.

Some firms like William Grant & Sons, in cooperation with other Scotch distillers, is working closely with cork producers to stop potential TCA infection at source.

In addition to a no chlorine regime, all of the firm’s corks are shipped in bags injected with argon gas. 

In other words, even with these safety checks, there will be the occasional incidence of corkiness. 

There are also potential issues at home or in bars. If you have used a chlorine-based cleaning product to wipe a work surface, for example, and then placed a cork on it, there could be chlorine contamination.

So, be aware. If you think there’s an issue, either return the offending bottle to the store – specialist retailers will know what you are talking about (if they don’t, take your business elsewhere) – or, better still, send it direct to the producer/bottler.