Thursday, 26 August 2010

€1,5bn Cork Dork Combat

It was just after I discovered that Bob was a fictitious character. My aunt insisted that one should never drink alone and Bob, at the very least, was always there to share a glass of wine with her.

I was also just beginning to think I knew a little bit about wine – and people - only to discover that corked wine is not when you have bits of cork bobbing in your wine glass and who Bob really was in my aunt’s life.

And so much later the thot continued to plicken. Polite conversations with sommeliers and friends could turn in a pop to heated debates, ‘Its Brett!’ (no relation to Bob, but a spoilage yeast), ‘its dirty barrels’, ‘its old filter pads’, ‘its volatile phenols!’ and so the debate raged.

Its true corked one wine can range from barely detectable to totally and utterly beyond consumption or any domestic use other than tie-dye staining some T shirts or macramé for 70s décor.

Cork Tree

It just depends on, well a whole raft of things: from which part the cork is harvested from the tree (close to the ground is a no no); how the cork was subsequently treated (chlorine is a no no) and stored until the jaws of a corking machine compress it and it’s driven into a bottle neck.

The aromas or rather odours have been described variously as dank and mouldy, wet dog, wet cardboard and wet hessian varying from a light veil over the wine to totally cloaking the fruit and smothering the intensity and length of wine - very depressing with a particularly special or expensive bottle of wine.

One significant cause of musty taint in wine is TCA (trichloroanisole) an organic compound which, for example, is produced when chlorine reacts with phenolic compounds (which include tannin), producing chlorophenols. Corks naturally contain lots of phenols and many species of mould will bring about the reaction.

However, no significant reduction of taint occurred after chlorine-based bleaching of corks was replaced by peroxide. The taint compounds are metabolic products of fungi naturally present in cork and on cork trees, or which have grown in the cork during processing and storage. Fortunately – or unfortunately - they cannot be seen, only smelt!

Amazingly, it’s incredibly potent since its aroma detection threshold is about 3-4 parts per trillion (ng/lt) and can be detected by professional oenologists at 3-10 parts per trillion. At 50 parts per trillion, the odour is much more noticeable and at 100 parts per trillion even beer drinkers can spot the difference.

The extent of the problem is hotly debated within the trade. A French journal La Vigne has reported that between 5-8% of bottles distributed in the French market are likely to be corked. Bob sure does get around.

More recently there is widespread agreement in the US that the occurrence of TCA has diminished for all types of cork products. Even Christian Butzke, a long time vocal critic of cork taint, has stated that “TCA is no longer a major problem for the US wine industry”. His findings at the Indy Wine Competition, similar to results posted from other recent venues, found cork taint to occur at levels at or below 1%.

These observations tie with the results seen by Cork Quality Council (CQC) members who have been testing every incoming cork lot for TCA since 2001.

Meanwhile, a recent closure trial conducted by the Australian Wine Research Institute (AWRI) supports the observation of many winemakers that cork finished wines compare favourably to alternatives in flavour complexity, development and balance.

The Technology

One of the most successful treatments is subjecting the cork to supercritical (above its temperature and pressure critical point) carbon dioxide. However it only works on composite or agglomerate corks. It’s a NASA-scale problem because cork lenticels (fine pores) will always harbour natural but highly evasive fungi.

Some producers use steam to remove most but not all of the TCA (whole natural corks) followed by gas chromatography-mass spectrometry to detect TCA followed by ozone as preventative measure in a case of extreme cork dork combat.

Rub of the Green

Portugal, one of the poorest countries in Western Europe, produces around 60% of the world’s corks. Their exports are close to €1 billion per annum of the total €1,5bn cork products market. However, a World Wildlife Fund report predicts that three quarters of the Western Mediterranean's cork oak forests could be lost by 2015 ('06 WWF scenario forecast) if the current trend to alternative closures and rising volumes of bottled wines continues.

In Portugal alone, the cork forest acts as a carbon sink for 4.8 million tons of CO2 each year while aluminium screw cap production has the highest CO2 emissions of all the closures.

The cork industry - in a brilliant stroke of PR after presumably feeling threatened by alternative closures – managed to get the WWF on its side in protecting its interests and the argument is compelling. The WWF has produced detailed reports sighting the economic, environmental and biodiversity importance of European cork forests including the fact that they are the home to species such as globally endangered Iberian Lynx, the Iberian Imperial Eagle and the Barbary Deer and among the highest ranked number of plant species in the world.

The Gadgets

If a consumer buys a bottle of tainted wine, is all lost? Not so, say two French researchers. Professor Gérard Michel and Oenologist Laurent Villaume have developed a carafe that removes TCA from tainted wine. The system works by using an ionised material known as a copolymer to absorb the TCA in the wine.

The affected wine is poured into a decanter and the copolymer – shaped like a bunch of grapes – is lowered into the wine and left until the taint disappears. Two single-use copolymers and one special decanter are included in the €6 (R50) pack. If it works, it’s an absolute steal when you discover your €5000 (R45 000) bottle of Domaine de la Romanée-Conti is corked.

According to its makers, the carafe takes from twenty minutes to two hours for the wine to recover its original characteristics. “To get this result we conducted thousands of tests and we used oenologists trained to detect cork taint on the nose at a level of two nanograms”, said Michel.

An alternative approach is Wine Rescue. Wine Rescue uses technology called Thin Layer Absorption. An activated carbon disk captures various compounds, such as TCA, by getting them to adhere to its surface, while letting the important flavour components pass through the filter. A bottle-top pump injects air into the bottle, pushing the wine up a dip tube and through the filter, after which the treated wine is dispensed into a decanter.

“Essentially, we are removing one chemical from a substance made up of hundreds or thousands of chemicals”, said Mike Havelka, president of Wine Rescue manufacturer, Vinterus Technologies. “Removing five parts per trillion of TCA in a bottle of wine is analogous to removing a tear from an Olympic-sized swimming pool”. Ok, so also unlikely to work then Bob.

However, the test of time and of trial and error is seeing screw cap converts returning to cork closures, choosing to live with cork taint lottery as cork offers greater maturation potential. Meanwhile screw cap producers are developing linings that offer the same nominal gas exchange that cork provides – the battle continues.    


See cork production on Youtube
For the latest on TCA & barrels
For winemaker-led tours of the cape

References: American Cork Quality Council


  1. "a World Wildlife Fund report predicts that three quarters of the Western Mediterranean's cork oak forests could be lost by 2015 if the current trend to metal screw caps and synthetic corks continues."

    What bolleaux! 3/4 lost in the next 5 years? Cork is used in many other products, not just as wine closures. And lets take a reality check here. There is a tremendous amount of wine being produced now compared with 30 years ago. You know this in South Africa, how mauch more are you making now? They weren't producing any Sauvignon Blanc in Marlborough then so if all that NZ Savvie is closed with screw caps now, it hasn't taken away anything from cork.

    And if a failure rate of 1% is not a major problem just wonder what the reaction would be if 1% of other food items were fouled by their packing when it could have packed in fault free packaging.

    Great bog -- look forward to reading more

  2. Thanks Peter, that WWF scenario forecast was made in May 06, see (pg 23, and i am sure was designed to catch attention) while cork stoppers comprise 70% of the value of the cork market - but again the data is a bit dated!

    As a wine maker i am a great proponent of screw cap for wines to be consumed within a couple of years fom vintage/bottling.