- The Washington Times - Tuesday, August 5, 2003

Natural corks, synthetic look-a-likes, plastic stoppers, screw caps. You may have noticed that even expensive, premium wines come equipped with a variety of different closures these days. You may wonder what’s going on.

Not so long ago, all but the cheapest bottles of plonk sported real corks. So why the change now, and what should you know about the different items being used to seal wine bottles?

The first thing to understand is why this issue matters at all. The choice of closure is hardly a concern with other beverages, alcoholic and nonalcoholic alike, but because wine is natural, never having been cooked or processed, it is particularly sensitive to oxygen. Because excessive exposure to air will turn any wine sour and vinegary, a tight seal in the bottle becomes essential.

About 300 years ago, when wines first began to be put in glass bottles, vintners searched for appropriate closures. Some used cloth and pitch, others stuffing and wax, still others glass stoppers tied down with wire. Before long, cork emerged as the item of choice. By 1800, virtually all bottled wines were sealed with it.

Made from the bark of a specific type of Mediterranean oak, Quercus suber, cork provides an excellent seal. Being pliable, it expands and contracts to fit snuggly in the bottleneck, and of course, it’s watertight and prevents leakage.

Paradoxically, what makes cork such a good closure is that the seal is imperfect. Ever so slightly porous, a cork will allow a very small amount of air to enter the bottle and affect the wine. This minimal exposure to oxygen can prove beneficial, particularly with wines designed for aging, as it can assist in the development of complexity and subtlety.

Unfortunately, cork has another imperfection. The bark has to be aged, boiled, cut and washed. As part of that process, it can pick up a taint, and that taint, in turn, can affect the wine that comes in contact with it.

This taint tends to be a specific chemical compound called “tri-chloro-anisole,” or TCA for short. Researchers speculate that it is introduced when the bark gets cleaned, particularly if the cleaning solution includes chlorine. Although harmless to health, TCA can prove disastrous when it comes to flavor. A small amount will make a wine taste dull, while a larger amount results in a musty, moldy, cardboardlike aroma. If you have ever had a glass of wine that smelled like an old trunk in a basement, you have experienced cork taint.

No one knows for certain how much wine is contaminated with TCA. Estimates range widely, anywhere from .05 percent to 25 percent. However, because everyone in the wine business knows that some bottles are infected, an increasing number of producers are trying alternative closures for their wines.

Because vintners do not want any of their wine to be tainted and no consumer wants to buy a spoiled product, you might think the days of cork’s dominance as a closure are numbered. They may well be, but two quite separate factors complicate matters. The first is that TCA can get into wine from other sources. The second is that no other closure works exactly like cork.

Researchers have located TCA in barrels, cleaning solutions and storage areas, pretty much any moist place where the compound might grow. Recently, a couple of prestigious California wineries, Beaulieu in Napa and Hanzell in Sonoma, found it in their cellars. This sort of taint can end up in a bottle of wine, but it clearly does not come from cork.

The other complication is that alternative closures simply do not perform like cork. This is not necessarily bad (and in many cases may actually be good), but it does render them different.

You’ll find two types of alternative closures in bottles at your local wine shop — screw caps and synthetics formed out of plastic. Made in a variety of different ways, synthetics resemble corks in that you need a corkscrew to extract them, but they have the advantage of being far less susceptible to TCA. Screw caps offer a more radical alternative because they bear no resemblance to cork and seem more akin to the sort of closure you find on soft drinks.

Of these, synthetics present problems. Because they are far less pliable than cork, they often do not provide a consistent seal running the length of the stopper. As a result, wines can lose their freshness quickly and taste dull and tired far too soon. This does not happen with all bottles sealed with synthetics, but it does occur frequently, with glass presenting an inherently uneven surface. And though a tired wine may be better than a severely tainted one, neither proves particularly pleasant.

The other problem with synthetics is that they can be quite difficult to remove and reinsert. Considerable muscle power may be needed, and they sometimes damage corkscrews, particularly Teflon-coated ones.

Screw caps offer many more advantages, and in fact seem very much the wave of the future. Made with a metal top and side enclosing a plastic gasket that compresses against the glass, they provide an almost perfect seal and allow no perceptible oxygen to reach the wine.

The Australian Wine Research Institute is in the process of conducting extensive closure trials. Though the evidence is incomplete, it seems clear that screw caps maintain excellent freshness. Many wineries Down Under are putting them on their wines, as are numerous producers in New Zealand as well as a small but growing number in California. Although some consumers associate them with cheap wines, screw caps in fact provide the best and most efficient closure available.

Beside the consumer perception problem, the one potential difficulty with screw caps concerns aging. No one knows for certain, because superior, age-worthy wines bottled with them have not been evaluated over the course of 20 or 30 years, but it seems likely that screw-capped bottles will age differently from cork-finished ones. After all, unlike with cork, the seal is total, so the maturation likely will be slower.

It is worth remembering, though, that only a small number of wines ever benefit from aging. Well over 95 percent of the wines in the American market are designed to be drunk upon release. For these, screw caps appear to provide the best closure.

The cork industry, faced with what in many respects is a superior product, is responding with a combination of product development, panic and propaganda. Manufacturers are investing millions of dollars in research designed to remove TCA from cork. They have not yet succeeded, and the jury remains out as to whether they ever will.

At the same time, cork producers are spending money lavishly on promotions that advertise cork as “classic” and “romantic.” This is pure nonsense. Wine has been part of human civilization for some 7,000 years. Cork in glass bottles has been widely used for but three centuries, and there is nothing remotely amorous about a piece of processed tree bark.

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