HUNTER VALLEY, Australia — In the course of working my way through a vertical tasting (multiple vintages of one wine) of superb, dry, crisp semillons from Brokenwood winery in the Hunter Valley district two hours’ drive north of Sydney, the subject of closures came up.

In wine circles, “closures” is not some psychobabble, but the generic term for whatever you use to seal a bottle of wine: traditional cork, screw cap, synthetic cork, or the newfangled glass cork where a silicone O-ring attached to a solid glass stopper seals the deal. What a winery chooses today says a lot not only about its sense of modernity or traditionalism, but also about its frustrations.

This became apparent when Brokenwood’s managing director and chief winemaker, Iain Riggs, mentioned that the winery had switched to using screw caps rather than corks.

Australia is in the forefront of screw cap advocacy. Whole regions, such as Clare Valley, have collectively discarded corks in favor of screw caps for wines such as riesling.

What was surprising, even eye-opening, was when Mr. Riggs declared, “We lost 30% to 40% of our semillon wines from oxidation due to corks.” When I repeated his assertion back to him just to make sure I had heard Mr. Riggs correctly, he confirmed that indeed the losses from oxidation were that high.

“We have had to throw out enormous numbers of bottles, especially those from the mid-1990s, because the wines were oxidized from faulty corks,” he said. “And it was not just a matter of winemaking, either. We made all sorts of wines in all sort of ways back then: low-added sulfur, relatively high-added sulfur, low-oxidation winemaking, higher oxidation winemaking, with and without skin contact, you name it. None of that mattered. It was the corks,” he said firmly. “It was not just us, remember. You had all those oxidized white Burgundies in the mid-’90s, too, with the same high losses from oxidation. Same reason, too. It was the corks.”

This issue of closures is roiling the wine industry and dividing wine lovers into traditionalist and modernist camps. Buyers of expensive white Burgundies are dismayed, even bitter, about the near-wholesale oxidation of the Burgundian chardonnays they bought from the 1996 vintage, as well as 1997 and 1998 vintages.

I myself bought numerous cases of 1996s, which when young had every likelihood of emerging as one of the great white Burgundy vintages of our time. Yet all of my premier and grand cru Chablis are now undrinkable due to excessive oxidation. I had to pour them down the drain.

According to Allen Meadows, who tastes thousands of Burgundies a year for his private newsletter, Burghound.com, “The premature oxidation of white Burgundies from the mid’90s is undeniable. Although the reasons are more nuanced than is usually reported, involving various winemaking reasons, bad corks are the final culprit in the chain. This is proved by the sheer randomness of the oxidation. You might find, say, four badly oxidized bottles out of a case of 12 bottles of the same wine, which happened to me recently. There’s your 30% failure rate right there.”

Everywhere in the world, winegrowers are struggling with their choices. Producers of luxury wines that trade on traditionalism, such as Bordeaux and Burgundy, are reluctant to abandon corks, although a few brave producers in both regions have done just that. After all, consumer surveys repeatedly show that most wine buyers prefer wines with corks. Nevertheless, the bandwagon for alternative closures continues to gain ground, nowhere more so than in Australia and New Zealand. In both countries, screw caps are not just frequently seen but commonplace, even for high-priced bottlings.

Are screw caps better? The jury is still out, although the evidence keeps mounting that they do keep wines more pristinely un-oxidized. For example, during my time in Hunter Valley, I worked my way through multiple vintages of one of the district’s greatest semillons, Tyrrell’s “Vat 1”. It is a benchmark bottling, an icon of the region.

Since their Vat 1 semillon is famed for aging and improving for decades, Tyrrell’s has more than a passing interest in insuring that this wine gets the best closure possible. They bottled their 1999 Vat 1 semillon as usual with cork and also, experimentally, with a screw cap.

Tasted side by side, the two wines were noticeably different. The cork-finished 1999 semillon had a medium-deep yellow/gold color typical of mature Hunter Valley semillon and offered a scent of coconut, which is a marker of maturity for this wine.

The screw cap version, in comparison, was a shade lighter in color with the slight greenish cast typical of young Hunter Valley semillons. Its scent was more mineral with noticeably less coconut. It tasted fresher, younger, and less evolved than the cork-finished version.

When I asked owner Bruce Tyrrell his conclusions about the desirability of screw caps, his succinct reply said it all: “Starting with the 2003 vintage, all of our Vat 1 semillon will have screw caps.”

As “Peanuts” creator Charles Schultz said, “Don’t worry about the world coming to an end today. It’s already tomorrow in Australia.” Indeed it is.