Cork. It’s more than a detail.

By Ben O’Donnell

In recent years, the shift from cork to screw cap seemed inevitable. Forward-thinking regions like Australia and New Zealand now use screw caps for around 70 percent and 90 percent, respectively, of all their wine to better protect the quality.

So it came as a surprise two years ago, when winemaker Adam Mason, working for South Africa’s Klein Constantia at the time, announced that he’d be returning the Perdeblokke Sauvignon Blanc to cork, after four vintages under screw cap—for technical reasons. Not long after, Christian Canute of Barossa’s Rusden Wines made the same switchback on the Driftsand Grenache-Syrah-Mourvèdre, after five years under metal, despite an Australian wine press hostile to cork. “There is a fear that non-conformity on this issue might affect how a producer’s wines are rated,” Canute told me.

Could it be possible that the screw cap is not the closure panacea it’s made out to be for all grapes and styles?

Screw caps eliminate two key problems in wine: muted, musty aromas from cork taint, which is caused by the chemical TCA that can form in the cork itself, and oxidation due to imperfect corks. But screw caps have their own issues, simply a function of how the cap works: Most seal the wine off from oxygen nearly entirely.

In winemaking, sulfur compounds, including volatile ones such as hydrogen sulfide (H2S) and mercaptans, can form naturally (along with the sulfur dioxide, or sulfites, added as a preservative). These usually blow off with exposure to oxygen, but in a wine starved of air, the volatile compounds can become trapped and possibly worsen in bottle. The result is “reduced” rotten-egg or stewed-cabbage aromas, the flip side of wines exposed to too much oxygen.

A winemaker’s stylistic decisions can abet reduction: from the choice of yeast (some produce more hydrogen sulfide) to extended fermentation to racking regimens to bottling an unfined and unfiltered wine. These otherwise sound techniques can all increase the level of potentially bad sulfur compounds, like mercaptans, during winemaking.

Even when apparently tamed into undetectable forms with oxygen exposure, such pests emerged again in the reductive environment under screw cap, Mason and Canute found. Fresh, screw-capped wines later opened up with nasty surprises.

Some grapes—like Sauvignon Blanc, Syrah and Pinot Noir—lend themselves to reductive winemaking, the deliberate effort to limit oxygen exposure. These varieties have delicate aromas and flavors that can be “irrevocably lost as a result of certain oxidative winemaking practices such as poorly timed or too-frequent racking of the wine,” explained Mason. You want to blow off any stinky sulfides without letting the enjoyable aromas and flavors float away.

Mason and Canute felt that using cork closures, which generally allow small amounts of oxygen to reach the wine, was the best option to manage the balance between oxidation and reduction for the cuvées in question. Why should winemakers need to ditch desirable techniques just so they can bottle under screw cap?

Undoubtedly, if you open a wine bottled under cork 10 or more years ago, you have a higher risk of cork taint than you will see in today’s bottlings: The closure debate has sparked major research and development initiatives in the cork world aimed at reducing the incidence of TCA. While someone my age finds the occasional corky bottle, frequent TCA frustrations may be the heartbreak of an earlier generation of drinkers.

There are other compelling reasons to reconsider cork today. For wineries concerned about their environmental impact, natural cork is sustainable, biodegradable and has generally been found to leave a smaller carbon footprint. A new consideration is the promising invention of the Coravin preservation system, which allows you to extract a glass of wine from a bottle without opening it, using a needle that penetrates the cork.

Yet like the cork companies, screw cap makers have been striving to improve, continuing to invent and refine liners with varying levels of oxygen permeability. And winemakers now have access to more options than ever, whether synthetics or bioplastics, like those from Nomacorc; cork composite, like Diam; or even alternative packaging, from cartons to kegs.

What’s the lesson here? The Great Closure Wars have taken to new battlegrounds: The debate of today plays out less in the opinion pages than in the cellars, where winemakers are fiddling with the whole spectrum of ways to seal wine to determine which best fits each bottling.

My exchanges with Mason and Canute demonstrate that some talented winemakers have found that they and their customers were unhappy with screw-capped wines—and cork fixed the problem. Making wine is an experiment itself, year-in and year-out, with a dizzying number of variables. I don’t think it makes sense to be more dogmatic about the absolute merits of a closure than we are about any of the other hundreds of decisions winemakers consider in the yearly roller-coaster ride to a solid wine.