The multilingual vocabulary of wine can make people feel tongue-tied, but the pop of a cork transcends all language barriers. There are few other sounds in the world quite so synonymous with celebration. Whether you’re opening a fine bottle of wine, a well-aged port, or even a cheap bottle of fizz, that pop announces the party.
Cork has been used as a stopper since the time of the ancient Greeks, but it wasn’t until the 17th century, and the advent of glass bottles, that it became the standard wine seal. Some of the advantages of cork closures are that they are watertight, sustainable, and good for color stabilization. Additionally, cork’s breathable nature allows the wine to develop over time with a small ingress of oxygen. It was the best—and practically only—option for centuries, providing over 95 percent of wine closures at its peak in the late 20th century. Today cork is used for more than 70 percent of closures, and more than 12 billion cork stoppers are produced each year, mainly from cork forests in Portugal and Spain.
Cork’s long employment in the wine industry has been attested by legendary discoveries of wine bottles under cork that have survived centuries in dusty cellars, kept in pristine condition. Cork was even able to preserve 70 bottles of Veuve Clicquot champagne that had been shipwrecked and submerged in the Baltic Sea for 170 years.
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There is, however, a downside to cork: 2.4.6-trichloroanisole, or TCA for short. When this volatile compound affects a bottle, the wine is simply said to be “corked.” TCA not only causes cork taint but contaminates wines with an off-putting smell resembling musty cupboards or wet cardboard.
The TCA level may be minute, but just 6 nanograms per liter (ng/l)—the equivalent of one drop in 20 Olympic-sized swimming pools—can ruin a wine. TCA contamination can come from storing a bottle in a contaminated environment (whether at the winery or a storage unit), but it can also occur in natural cork.
The level of TCA—or cork taint—in bottles grew so high in the 1990s that in the early 2000s Australia and New Zealand all but abandoned cork in favor of screw caps and other closures. Winemakers claimed they were getting stiffed by cork producers, as a much higher rate of cork taint was occurring there than in other wine-producing countries, and while evidence of foul play was only anecdotal, it was enough to persuade over 90 percent of New Zealand’s wine industry, and 70 percent of Australia’s, to boycott cork altogether.
“We went through a period in the late 1990s and early 2000s when there were many examples of badly TCA-affected parcels of cork,” explains Sandro Mosele, a winemaker for Ten Minutes by Tractor, a Main Ridge, Australia, winery. “There were parcels in excess of 50 percent. I have not heard of such crazy numbers in recent times; nevertheless, TCA-affected bottles still occur. It would be very unlikely that we would consider future bottlings under cork… We use the most predictable closure, which until this point, is the screw cap.”
The cork industry, however, was not going to give up that easily. The world’s largest cork producer, Amorim, is now on a mission to eliminate TCA from corks by 2020, and its competitors are following suit. The success of Amorim and the other producers will be measured by their ability to assure TCA-free corks, but it will also be highly dependent on the rise and fall of other closures. While the cork industry has been struggling to remove the bad taste left by the unpleasant side effects of TCA, alternative wine closures began to proliferate. But do any other closures measure up to the virtues of cork?
In Australia, following the cork scandal, the main replacement was metal screw caps that twisted onto the bottle neck. Screw caps are airtight, watertight, and free of TCA and cost around 12 cents per unit, compared with a good-quality natural cork, which would set a producer back around 50 cents. The downside is that they can have a reductive effect on the wine, inhibiting the evolution that occurs over time through oxygen ingress. For some producers, though—and wine styles—this more consistent, and lower, rate of oxidation is actually an advantage.
“I use screw caps on Casillero del Diablo wines [$7–$13 per bottle retail] because they are reliable, with no risk of getting a corked bottle, and they are easy to use and good for wines that are ready to drink today,” says Marcelo Papa, winemaker at Concha y Toro, outside Santiago, Chile, which produces over 13 million cases of wine each year. “However for Marques de Casa Concha [$15–$20 per bottle retail], I like natural cork because of the evolution it gives to a good wine. But I’m still very frustrated when I find a corked bottle.”
Synthetic corks are another alternative to natural cork; they make up around 8 percent of the global closures market. They’re great for marketing as they come in a range of colors, but they tend to have a cheaper look, which is off-putting to the premium market. The other big negative is that synthetic corks can also have an oxidative effect, and they can pick up TCA contamination from the external environment. The quality of synthetic corks varies greatly though, and they can cost anywhere between 9 cents and 32 cents.
At the top end of the market, technical corks such as those made by Diam by fusing together pieces of natural cork are among the most popular alternative bottle stoppers. The great benefit with Diam corks is that a carbon dioxide treatment process eliminates volatile molecules that might lead to TCA taint. Diam now produces over 1.25 billion technical corks a year, an enormous number considering they launched their first technical cork just 12 years ago. A drawback, though, is the relatively high price (a Diam “10 stopper” costs around 28 cents) and a cheaper appearance. Nevertheless, technical corks are a popular alternative for premium, age-worthy wines, especially for sparkling wines, in which TCA is particularly perceptible but ageability is essential.
“The only quality options for sparkling wine are cork or cork-based products such as Diam,” says Emma Rica, the head winemaker at Hattingley Valley, a premium sparkling wine producer in the U.K.. “We use Diam closures on all our wines for consistency and their reliability for no TCA.”
There are also a number of less widely adopted but no less functional stoppers, among them the reusable glass Vinolok and the resealable, twisty Helix cork. Each has its own pros and cons, but none have yet surpassed the use of traditional, natural wine corks, which still hold the lead in the industry. And the largest cork producer, Amorim, hopes that its ambitious plan to remove TCA risk from corks completely will keep it that way.
“We had 10 to 20 really difficult years, where everyone said the cork industry would end,” admits CEO Antonio Amorim. “Screw caps shook the status quo of the industry, but we decided to stay in cork because the room for improvement was enormous. The focus of our research and development has been on TCA, and we will totally eliminate TCA in corks by 2020.”
Considering that Amorim has already brought down its TCA screening levels from 10 ng/l in 2008 to just 0.5 ng/l in 2015 (a concentration considered undetectable by the Australian Wine Research Institute), that goal seems feasible. Amorim has, in fact, already developed a natural cork with nondetectable levels of TCA through its NDtech screening technology.
Cork trees have been harvested in the same way for centuries and that’s unlikely to change; the processing of cork bark, however, has become practically unrecognizable in the last few years. The cork bark from Quercus suber trees goes through several selection processes—in the forest, in the processing plant, during stabilization, during steam treatment, and in the final cork production line—where it’s separated into several different grades. Only 5 percent to 10 percent of the bark will make the final cut for single-piece wine corks. And that small percentage comes after approximately 43 years of life as a cork tree in the forest.
While some corks are still punched out into whole pieces by the traditional method, the rigorous testing of those corks now features X-rays, sensors (human, chemical, and robotic), and pressure tests to spot any faults that could lead to TCA contamination, as well as a combination of five technologies that steam, treat, and heat cork to remove all the volatile compounds.
“When I told my 89-year-old father that every disk of cork now goes through an X-ray, he thought I was crazy,” says Amorim, who represents the fourth generation of the family business and has invested over €2.5 million in the last year on eradicating TCA (including the purchase of several €200,000 X-ray machines). “But since 2009, the cork industry has started to grow again—by 4 percent in general, and Amorim by 8 percent.”
The proof is in the pudding, as they say, and the rigorous testing, by the producers as well as within the market, is showing results. All the natural corks that arrive in the U.S. for wine production are analyzed on arrival and show a 95 percent reduction in TCA since 2002. This assurance does come at a price—the best tried-and-tested TCA-free whole-piece natural corks will cost upwards of 50 cents per unit, meaning that they’re only reserved for premium wines.
“Wines taste different when they are sealed with different closures, and I think some wines do taste better under cork,” says wine critic Jamie Goode, who tastes on average 9,000 wines a year. “The problem with cork has been its consistency, and the lower—but still prevalent—rate of taint is still troubling. But now there are lots of options open to winemakers, and it is almost a way of differentiating their range of wines: they might use screw cap for the entry level wines, and cork for their top of range. Certain markets also demand certain closures.”
In a surprising turn of events, the use of cork is now on the upswing in Australia too. In spite of their reluctance to return to natural cork, Australian producers are bottling under natural cork once again for the Asian market—their biggest market today—because consumers associate cork with quality.
Drinking wine is, ultimately, all about pleasure. And although it might take convincing to get some producers back on board with cork, for many consumers part of the pleasure of opening a great bottle of wine is hearing the cork give you that little celebratory pop.
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Amanda Barnes is a British wine writer who since 2009 has been based in South America, where she specializes in the wines and regions of Argentina, Chile, Brazil, and Uruguay and writes the South America Wine Guide. Ever footloose, she is currently on a mission to travel Around the World in 80 Harvests.