We’ve all heard–and probably muttered–aphorisms to explain the disappointment after opening and tasting what was supposed to be a “great wine.” The most common explanation is “bottle variation,” as in, “I had a great bottle of that wine only last week,” or ‘the last bottle of that wine showed much better than this one.” Someone invokes the cliché, “It just goes to show you there are no great wines, only great bottles of wine.”
I maintain that the explanation for bottle variation–a very real 
phenomenon–is the inherent inconsistency of using corks as closure for wine.
I’m not speaking of an obviously “corked” wine, those whose cork has been contaminated by 2,4,6-trichloroanisole (TCA), a chemical that imparts a musty, wet cardboard or wet basement-like aroma to the wine. Those wines represent just the tip of the iceberg. I believe that bottle variation comes from using corks at all. All corks, by their very nature, have the potential to fail–to a greater or lesser degree–and change the character of the wine. This failure rate explains bottle variation, how two wines from the same case stored under identical conditions taste different.
But I wouldn’t jump to screw caps just yet.
Stripped Wine
More prevalent and harder to detect than overt corkiness, is a cork taint that strips the flavor, aroma and fruit from the wine in the absence of perceptible TCA aroma. This defect is detected only when tasting–or drinking–a wine you know well. Occasionally, when tasting a producer’s wines with the winemaker, I will run across a bottle that is not exciting, but not flawed, at least to my palate. The winemaker, clearly unhappy with it, opens another bottle that turns out to be very different, vibrant and full of life. If I weren’t tasting with someone who knew the wine well, I never would have known it was an ‘off’ bottle, I would have assumed in was a mediocre wine.
Sometimes you can identify the problem yourself. Not long ago I opened a half-bottle of 1990 Château de Rochemorin from my cellar. I had purchased a case and had been drinking and enjoying bottles periodically over the years, but this one was disappointing, lacking fruit and vitality. At first, I figured I had just waited too long, that the wine was past its prime, not unreasonable for an 18-year old wine in half bottle. I opened another one, figuring that, if they were all past their prime, better 
to know sooner rather than later. To my surprise, the second bottle was wonderful: mature, balanced, and not at all tired. These two half-bottles came from the same case, and were stored identically, so the only explanation for the dramatic difference between them was the cork.
Of course, bottle variation can be caused by different storage conditions, or by consuming the same wine at different temperatures, or, not least important, the overall setting in which the wine is consumed. But I am convinced from my experience with the Rochemorin and other wines that I’ve been lucky to taste repeatedly that some bottles ‘show’ far better than others. I suspect the main reason is the cork.
I have no idea what the precise defect in the cork of my bottle of Rochemorin eviscerated the wine. Was it subtle TCA that I failed to perceive? Or was it other chemicals in the cork, or did the cork “fail” in some way?
Jacques Lardière, the legendary winemaker at one of Burgundy’s best houses, Maison Louis Jadot, noted that sometimes the wine in an individual cask appears stripped compared to its neighbor. He believes it comes from opening the cask too often for tasting, perturbing the oxidation/reduction balance. After leaving the barrel untouched, the wine comes back into form.
2,4,6-Trichloroanisole, Better Known as TCA
A small number–estimates vary from 1-7 percent–of corks are contaminated with TCA (2,4,6-trichloroanisole), which is the major chemical thought to be responsible for the cardboard-like aroma we identify as ‘corkiness.’ The precise origin of TCA in corks is uncertain. The most prominent explanation is that fungi normally found in cork and generally considered to be beneficial to it, convert a group of chemicals called chlorphenols to TCA. Chlorphenols as a group are industrial pollutants that can wind up in the bark–the part of the tree used for cork–via the roots 
absorbing contaminated ground water. Other research suggests that TCA is a breakdown product of other pollutants, such as PCP, or can be a by-product of chlorine bleaching of corks, a technique, now largely abandoned, but formerly used to sterilize them.
Often the unpleasant aroma of TCA is immediately identifiable when the wine is offered for tasting, as most people’s noses can perceive extraordinary small amounts of it. But sometimes, it has a very subtle effect, and even experienced tasters miss it at first. The wet cardboard or wet basement-like aroma worsens as the wine warms in the glass and as TCA becomes more volatile and is easier to perceive. Peter MF Sichel, a prominent figure in the Bordeaux wine trade, maintains that when there is a question as to whether a wine is corked, adding a drop or two of water to the glass, will increase the off smell.
Overt TCA-affected wines seem to be more common today than decades ago. Some blame an increased demand leading to harvesting younger cork. The increasing presence of chlorphenols in ground water related to increased industrial pollutants likely plays a role. But older bottles are not immune to the problem. Sadly, a year or two ago, a bottle of 1961 Chateau Latour brought by an acquaintance to dinner was undrinkable because of the cork taint.
In my entirely unscientific observations, overt corkiness in 
Champagne occurs less frequently than in still wines. The Champagne cork is fundamentally different because it starts as a large cylinder, but eventually transforms into the familiar mushroom shape. Is there something in that process that inhibits the formation of TCA? Or is the cork for Champagne bottles different from the cork used for still wines?
Confusion Reigns
What exactly is the purpose of the cork? Certainly it seals–to a greater or lesser degree–the bottle. Wine left open oxidizes and tastes awful after a few days, so preventing a lot of air from coming in contact with the wine is a good thing. Corks do that very well, by swelling and contracting in response to moisture to remain snug against the sides of the neck of the bottle.
But does the cork allow any air to come in contact with the wine, which could potentially spoil (oxidize) it? Or allow it to age gracefully? Some in the industry–prominent wine writers and winemakers included–insist that air does not penetrate the cork because the seal is tight. They stumble when asked to explain the common phenomenon of ullage, or the loss of wine from a bottle during aging. In the absence of obvious leakage around the cork, how else could the wine escape from the bottle except through the cork?
Some prominent winemakers–such as Leroy, a producer whose Burgundies are among the most expensive from that region– think that air does penetrate the cork and come in contact with the wine, a potential hazard in their view. They use corks, but then cover them with a wax seal to prevent air movement. There is not universal agreement even among high-end producers. The Domaine de la Romanée Conti, another prestigious Burgundy producer whose wines also sell for thousands of dollars a bottle–also uses corks, but without wax seals. So who’s right? Wines from both the DRC and Domaine Leroy age and develop beautifully, so maybe air is not all that important.
Don’t Jump to Screw Caps
Many producers vehemently advocate screw caps to eliminate the problem with TCA and bottle variation entirely. But our knowledge of long-term–20+ years–of aging wine closed by screw caps is limited. True, the vast majority of consumers do not age wine, but a small and important minority do. A half bottle of 1983 Bâtard Montrachet from Louis Latour that I had earlier this year was exquisite, with mature flavors balanced by a vibrant freshness. Would it have developed the same way under screw cap? I don’t know, but to me, the verdict is still out.
Before embracing screw caps as THE answer, let’s remember that California’s answer to phylloxera was using AXR rootstock–supposedly resistant to the pest–exclusively. The result was massive replanting in the early 1990s as it became apparent that AXR did not live up to expectations. Sometimes, we’re not as smart as we think we are. We may be better served by using a variety of closures, turning to screw caps for aromatic whites meant to be drunk soon, or fruity reds not suitable for aging. With less demand for cork and more research into what its defects are, we may be able to eliminate the problem.
When cork works as intended, the resulting well-aged wine is unbeatable.
Questions or comments? e-mail me at [email protected]