Most of the press trips that wine, spirits, and beer writers are invited on focus on what goes into the bottles we drink. In July, I was invited to Spain for a trip dedicated instead to the part that seals so many of those bottles: cork. Corks are one of those things we tend not to think about until they malfunction by crumbling apart, oxygenating a wine, or introducing “cork taint.” The growing acceptance of screw caps and synthetic corks is partly a response to the challenges of using natural cork. Our host in Spain, Diam, is a company that makes a sort of hybrid technological cork, combining natural cork material with new techniques for removing impurities and increasing consistency. They brought us to their facility in San Vicente de Alcantara to show off the process.
Preparing for this trip, I had romantic visions of the cork forests of Spain and Portugal. These visions were eventually fulfilled on an evening trek into the countryside, as seen in the photos above.
However most of our visit was spent here to learn about Diam’s technological process for transforming bark from cork trees into reliable stoppers that won’t ruin a bottle of wine. This was more industrial than romantic, but it was a fascinating learning experience.
We arrived a little too late in the season to see the local cork harvest, but the photo above (provided by Diam) shows how it’s done. The bark of cork trees is rich in suberin, a rubbery, waxy substance. In nature, the suberin prevents water loss by keeping moisture inside the tree. This same quality makes it great for keeping wine locked inside bottles.
Slaking the world’s thirst for wine requires a lot of cork. (Above: piles of fresh cork bark awaiting processing at Diam; you can barely make out a few people working on top.) Fortunately, harvesting bark doesn’t kill the trees, and after reaching maturity each tree can be harvested about once every decade. Driving through this region of Spain and Portugal, the brightly colored trunks of recently stripped trees stand out along the roadside.
After processing, traditional corks are made by punching through the bark. Obviously punched corks can only be extracted from sufficiently thick bark and much of the material is left behind. This can be put to other uses, including the technological corks made by Diam.
Here my friend Baylen demonstrates his invention of cork knuckles. Not a product offered by Diam — yet.
The Diam process begins by grinding the bark and sorting out the suberin-rich powder, which they call “cork flour,” so that it can eventually be reformed into a cork shape with food safe binders and microspheres. Agglomerated corks have been around in some form for years; it’s the step prior to agglomeration in which things get interesting.
Diam’s biggest innovation is treating this cork flour with supercritical carbon dioxide. In a supercritical state, created under very high pressure, fluids take on properties of liquids and gases. They are able to both permeate a substance and dissolve materials. By fine-tuning pressure and temperature to control its density, supercritical CO2 can be used to extract some substances while leaving others behind. If you drink decaffeineated coffee, there’s a good chance the beans you brew were treated in this way. The CO2 process is one of the main methods used to selectively extract caffeine from green beans.
Diam uses this same process to remove impurities from cork. The most important of these are TCA and TCB, the chemicals associated with cork taint. But lots of other stuff gets removed too, resulting in a cork that is neutral in its potential flavor impact on wine. (Above: quality control testing of corks by infusing them in water.)
A neat advantage of making corks this way is that other characteristics can be controlled too. By varying the elasticity of the corks, Diam can design them for less expensive, short-term aging, or for higher end wines intended to age for years. The box above shows their 1, 3, 5, and 10 year corks; they’ve also recently introduced a cork designed to last for 30 years.
They’re also able to control the permeability of the corks. Corks are naturally permeable, but a cork allowing too much air into a wine can ruin it. On the other hand, depending on the wine, a little bit of oxygenation could be a good thing. These corks come in varying degrees of permeability, allowing wine makers to choose the corks best suited to their wines.
Though conversation about corks tends to revolve mostly around wine, Diam also uses its process to make corks for beer and spirits (photo above courtesy of Diam). The corks for spirits raised an interesting question for me. I’ve rarely come across spirits I’d identify as suffering from cork taint, but on the few occasions I have the off aromas have surpassed anything I’ve come across in wine. Since spirits are much higher in alcohol than wines, and since alcohol is such a good solvent, I’d have thought that TCA would be an even bigger problem for spirits than it is for wine. Yet we rarely hear about spirits being “corked.”
As it turns out, I was half right. Spirits are a more effective solvent. But the team at Diam directed me to a scientific paper evaluating tasters’ ability to detect TCA in cognac, and it turns out the threshold level for perceiving it is much higher. The paper is in French, but in loose translation the tainted spirits had aromas of “mold, mushroom, wet mop, etc.” However the concentrations needed to perceive these notes unambiguously appear to be an order of magnitude larger than for wine. Higher alcohol seems to have a masking effect for the TCA. (I suspect that the tendency to store wine on its side, in contact with cork, and to store spirits standing vertically may also be a factor, but I don’t know for sure.)
One funny aspect of the Diam corks is that, at the insistence of wine makers, they have striations printed on them to mimic natural cork. A casual consumer could pull one out with a corkscrew and never notice the difference. Seeing the unfinished Diam corks come out and then get printed to resemble their purely natural punched cousins reminded me, of all things, of Howard Roark’s critique of the Parthenon in The Fountainhead:
“Look,” said Roark. “The famous flutings on the famous columns — what are they there for? To hide the joints in wood — when columns were made of wood, only these aren’t, they’re marble. The triglyphs, what are they? Wood. Wooden beams, the way they had to be laid when people began to build wooden shacks. Your Greeks took marble and they made copies of their wooden structures out of it, because others had done it that way. Then your masters of the Renaissance came along and made copies in plaster of copies in marble of copies in wood. Now here we are, making copies in steel and concrete of copies in plaster of copies in marble of copies in wood. Why?”
Because wine is tied up with tradition, that’s why. Despite the rise of synthetic stoppers, screw caps, and wine that comes in kegs and boxes, people still want to pull a plug of wood out of a bottle neck, even if that means occasionally dumping a corked bottle down the drain. And for wines that are meant for aging, corks are still one of most proven tools.
Are all these new high-tech corks really necessary? Claims about the rate of cork contamination are controversial. For one thing, cork isn’t the only source of TCA; it can enter wine at other stages of the production process, but the final consumer will declare the wine to be “corked” regardless of whether the cork is the actual source. Other defects, real or imagined, may also be attributed to the cork. (Working for several years in a top wine bar, it wasn’t uncommon to have “corked” wines returned that seemed fine to me. Did customers imagine it or just not like the wines? Am I less sensitive to TCA than other consumers? I suspect it was a little of both.)
Estimates of the rate of cork contamination range from 7% at the very high end to under 1% on the low end. The Cork Quality Council claims that rates have dropped more than 80% in the past decade thanks to improvements in the industry; they have a website, CorkTaint.com, dedicated to rehabilitating cork’s image and promoting studies showing low rates of contamination. Diam, for its part, declined to wed itself to a particular number.
Still, no one likes to open up a special bottle of wine to find that it’s been ruined by a fault that could have been prevented. The market now offers a lot of options varying in price, consistency, and longevity for sealing different wines, all of which have their place. The Diam corks are an interesting addition to that spectrum. I’m not a winemaker, nor do I pretend to possess the expertise to say which closures are best for which wines, but after this visit I certainly wouldn’t mind finding a higher tech cork in the next bottle I open.