One of the frustrations for wine lovers is the risk that when a bottle is opened, it’s faulty. And cork taint is the most commonly encountered fault in wine. In some proportion of bottles sealed with a natural cork, the wine will develop musty off-aromas that may strip it of flavor or make it undrinkable. It’s largely because of cork taint that we have the restaurant ritual of tasting a small sip of the wine we’ve ordered before it is poured.
How big is the problem? Current estimates range from one to five percent of cork-sealed bottles.
Although cork taint is as old as the use of cork as a closure, it became a topic of intense debate in the late 1990s. The global expansion of the market for wine put pressure on cork suppliers, most of whom are in Portugal. Increased demand exposed cracks in the system, and taint rates climbed significantly. Producers in New World regions came to believe they were receiving inferior corks; in Australia, anecdotal evidence suggests that taint rates were in excess of ten percent. And there was inconsistency in the closures, with some bottles aging much faster than others.
The search for alternative closures stepped up, and the Australians turned to the screwcap. In South Australia’s Clare Valley, a group of 14 riesling producers banded together in the 2000 vintage, bottling under screwcap. Their success soon led others to adapt, and screwcaps became the main closure in both Australia and New Zealand. Meanwhile, as synthetic corks slowly improved, they began to gain traction elsewhere. Facing the threat of losing much of their business, the cork industry responded by implementing preventive measures, including new cork storage and washing protocols.
It’s likely these improved production methods contributed to a reduction in taint, but it wasn’t enough. For natural cork to sustain a large market share in the face of taint-free alternatives, more action was required. The challenge has been to remove taint compounds—the chief one being the potent, musty-smelling 2,4,6-tricholoroanisole (TCA)—without altering the cork’s desirable properties.
The first technology for eliminating cork taint was introduced in 2004 by Amorim, the world’s largest cork producer—responsible for some 40 percent of the premium natural cork market. Dubbed ROSA (for ‘rate of optimal steam application’), it aimed to remove TCA by applying a steam treatment. Initially it was only suitable for cork granules that were used to make technical corks.
Technical corks—made up of small pieces of cork that are then glued together with a food-grade binder—account for 45 percent of the cork market. They are a cost-effective solution, but if they are made up of uncleaned granules, they can end up spreading cork taint evenly among all of the closures. In some cases, this averaged level would be undetectable, but in other batches it might result in tainting all the wines they sealed. Just a slight presence of taint is enough to spell disaster.
A notorious example developed in the technical cork Altec. Launched by Sabaté in 1995, Altec was a market success, with four billion closures sold by 2003. That year, though, four court cases with large American wineries were settled because some batches had tainted all their wines. This led Sabaté to work with a new process that involved the use of critical point carbon dioxide (at a certain combination of pressure and temperature, carbon dioxide is neither a liquid or a gas, but has properties of both). Through the process, critical point carbon dioxide penetrates the cork and extracts impurities, including the taint-forming TCA. But the process is only effective for granules, as it deforms intact punched corks. Oeneo—the successor company to Sabaté—thus adapted the Altec to produce what is now known as DIAM, which is a taint-free technical cork. DIAM has proven extremely successful in the marketplace, even for high-end wines.
Amorim stepped up their game, adapting their ROSA technique for use with whole cork stoppers in 2005. But steam wasn’t as effective as critical point carbon dioxide, and some tainted corks still got through. “Since then, over the last few years we have been upgrading ROSA, optimizing the conditions to get better extraction,” says Dr. Paulo Lopes, R&D manager of Amorim. “In 2016, we felt we had reached the full capacity of this treatment, and it was also the year we launched NDTech.”
Developed in conjunction with Ellutia Chromatography Solutions, a spin off from the University of Cambridge, NDTech involves assessing individual corks by GC-MS (gas chromatography-mass spectrometry) and rejecting any that have releasable TCA above 0.5 nanograms per liter. This is below the threshold of detection for humans. For the first time ever, wineries willing to pay the extra cost could pretty much guarantee that their wines wouldn’t be corked. Currently Amorim has 60 machines; each is capable of examining a cork in just 16 seconds. The speed may be impressive, but considering the volume of intact punched corks produced, the capacity is limited. And the company has faced a second issue with NDTech: false positives, ending up in unfairly rejected corks.
This led Amorim to work on a cleaning system for natural cork that delivers better results than ROSA. Carlos de Jesus, director of marketing and communications at Amorim, says that Naturity, launched in January 2021, will cover all the natural whole cork stoppers the company produces. “NDTech is a very expensive operation, and we could not expand that to the entirety of our natural cork range,” he says. “We needed to come up with something that extended the non-detectable TCA performance to the lowest grades of cork.”
The principle behind Naturity is thermal desorption using pressure variation. “It will allow us to break the bond that TCA has to the cork, creating conditions where we can do this at moderate temperatures,” says Lopes. “In reality, if you want to vaporize the TCA out of the cork you need [temperatures] around 240° Centigrade at atmospheric pressure. You can create different conditions when you can move this boiling point from 240°C down to 40 or 50°C.” If the pressure is reduced, then this boiling point comes down to 40 or 50°C, temperatures that won’t damage the cork structure.
Naturity is now being applied to Amorim’s full production of natural cork stoppers at no extra cost to the customer. “This last year and a half we have been preparing all the facilities and installing the necessary number of machines,” says Lopes.
But it is not just Amorim who has been busy working on curative solutions. Cork Supply is the second biggest cork company, responsible for 15 to 20 percent of the premium market for natural cork. In June 2020, they launched their own technique for cleaning cork, InnoCork Circuit, which is a combination of two processes: InnoCork and PureCork. “We started putting the first equipment in in June,” says Cork Supply founder and president Jochen Michalski. “Then in October we installed two more units, and the three units have enough capacity for us to do 100 percent of [our] corks.”
Cork Supply already had a process called DS100 where they individually do sensory analysis on each cork, in a human-based equivalent to NDTech for premium wine corks. “It is quite expensive to do,” says Michalski. “We now have an industrial process so we don’t have to sniff each cork. With this system, we will be able to reduce TCA to, basically, zero.” He adds, “I hate saying ‘zero’ because I don’t think zero exists in any business. I say 99.85 percent accuracy.” Like Amorim, Cork Supply will not increase the cost of its corks to cover the new processing.
Ana Cardoso, Cork Supply’s R&D director, explains the system. “From an engineering perspective, it is not that hard to remove volatiles from a matrix like cork. The issue is preserving all the cork properties,” she says. “For the last fifteen years we have been using steam-distillation processes. They are capable of detaching the TCA molecule from the matrix. Steam increases the temperature, so it reduces the attachment, and, also, the steam itself affects the properties of the volatilization of the gases. So, we have reduced the vapor pressure of TCA and are, at the same time, detaching and volatilizing the TCA better.”
InnoCork uses just steam, but while that is fine for granules, it damages the properties of punched natural corks. “For natural corks, our Innocork Circuit system is using ethanol as well as steam,” says Cardoso. The addition of the ethanol step, which is the essence of PureCork, means that they can work at lower temperatures and with a longer cycle, allowing the extraction of impurities while preserving the qualities of the natural corks. “With PureCork we have a gentler 24-hour process that doesn’t destroy the cork,” says Michalski.
Will cork taint be a thing of the past? These two technologies, applied by the two largest players in the cork market, together accounting for 55 to 60 percent of natural corks produced, have the potential to reduce it further. While it has been possible to clean granules for technical corks for a while, the significance of these solutions is that they are effective at cleaning punched natural cork stoppers while retaining their desirable physical properties. This should help winery owners and wine collectors sleep more soundly, and put cork sniffers out of business. It may also help preserve or even grow the market share of natural cork.
An earlier version of this story was published online as a news piece in January.
Based in London, Jamie Goode is a lapsed scientist who now devotes his time to writing about wine, mainly in the UK national newspaper the Sunday Express, and on his own site, wineanorak.com. The author of The Science of Wine (UC Press 2014) and I Taste Red (2016).
This story appears in the print issue of April 2021.
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