A friend of mine was irritated—outraged, really—by a video on Wine Spectator's Web site. My colleague Bruce Sanderson spoke with Chablis producer -Michel Laroche on the subject of screw caps, about which Laroche is both passionate and proactive.
Laroche had Sanderson compare two identical 2002 Chablis wines bottled from the same tank, one sealed under screw cap and the other with a cork. Sanderson observed that the screw-cap version was "much fruitier" than the cork version.
Frankly, it seemed pretty straightforward to me, as well as absolutely consistent with similar tastings I've done with winemakers. The screw-capped wine invariably emerges fresher, fruitier and more precise in flavor definition.
So I was surprised when my friend sputtered that this video was "unbelievable propaganda" with "no mention of the other side of the story."
What is it about screw caps that gets people so riled? Traditionalists enjoy the ritual of cork-pulling, which I understand. Others find the aesthetic of screw caps a bit too industrial, which I can see as well. But the fact is—and it is a fact—that screw caps work extremely well. They preserve wines with a greater degree of freshness than do other closures.
What, then, is the "other side of the story"? Namely, that if a winery is going to use screw caps, they might have to make their wines a bit differently to prevent the development of sulfide characters, which typically produce rubbery or burnt-match odors.
These smells have certainly occurred with wines under screw cap. But winemakers can effectively sidestep sulfide characters by employing different techniques in their winemaking and cellaring processes that vary depending on whether the wine is white or red. What you do before you reach, er, closure, is critical. When a wine is under screw cap, it's a version of the Las Vegas slogan: Whatever goes in, stays in.
So what's the "truth" about screw caps? Some facts are emerging, free of the public relations spin from both the cork and screw-cap contingents. One of the newest studies is by four members of the enology faculty of the Université Victor Segalen in Bordeaux, and was recently published in English in the trade magazine Practical Winery & Vineyard.
The key issue about screw caps—indeed about all closures—is how permeable they are to oxygen. This is precisely what the French researchers examined. They compared the "kinetics of oxygen ingress" between corks, various synthetic closures and screw caps over a three-year period.
One clever element of the study was how the researchers determined the amount of oxygen ingress in the bottle without having to insert anything. They used a solution that changed color when exposed to oxygen. The oxygen ingress was then measured by colori-metric scan.
So what did they discover? First, that commonly used synthetic corks had the highest oxygen permeation. Natural cork had medium levels of oxygen permeation, although—not surprisingly—the best-grade corks admitted less oxygen than did lower-grade corks.
And what about screw caps? Interestingly, screw caps sealed in more oxygen during bottling than did other closures, because oxygen remained underneath the screw cap when it was attached to the bottle. However, the researchers found that when in place, "screw caps allowed the ingress of consistent low amounts of oxygen, with no significant differences between manufacturers."
Oh, and one other thing emerged as a by-product of this study that's noteworthy: "Bottle storage orientation (upright or lying down) had little impact on oxygen ingress through most of the closures, at least over the first 28 months."
"Even in upright storage," the authors note, "the relative humid-ity inside a bottle is maintained at 100 percent, which allows the absorption of considerable amounts of moisture by the corks."
This point is important because it underscores that the whole bugaboo about the necessity of high humidity in a home wine cellar is piffle. Cellar humidity is important only for wines stored in wood barrels, not tightly sealed glass bottles.
The bottom line: Screw caps admit the least amount of oxygen, corks are in the middle range, and synthetics are the worst. If you're making a pristine white wine like Michel Laroche's Chablis—and your winemaking techniques recognize the unforgiving effect of the extremely low oxidation allowed by screw caps—then screw caps are indeed the ticket.
Matt Kramer has contributed regularly to Wine Spectator since 1985.
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