What is “Corked” Wine?

By Marc R. Kauffman, CSW, Certified Sommelier

Picture this: You are ready to enjoy a great bottle of wine. You manage to remove the cork, pour yourself a glass and gently inhale the aroma. Hmmm... It smells strange. This wine is corked. “But how can that be?” you ask yourself, because you have removed the cork from the bottle. What is corked wine? A corked wine is a wine that has been closed with cork containing a fungus known as 2,4,6-trichloranisole or TCA. This chemical is responsible for the wet newspaper musty aroma wine can pick up from corks. A wine tainted with TCA is said to be “corked”.

To figure this out let's look at the cork. Isn't it amazing that after almost 350 years of putting wine in glass bottles, the best sealing solution our advanced civilization has come up with is sticking a hunk of tree bark into the top of the bottle? However, the familiar pop of a cork as it leaves a bottle will probably be heard for many decades to come.

Cork’s structural composition is remarkable. A one inch cube contains roughly 200,000 14 sided cells filled with air. The cork itself is highly elastic, capable of snapping back to its original shape after withstanding 14,000 pounds of pressure per cubic inch. Cork is impervious to air, almost impermeable by water, difficult to burn, resistant to temperature changes and vibration, does not rot, and has the ability to mold itself to the contour of its container.

Most cork today comes from Portugal, however Spain, Sardinia, Algeria, Tunisia and Morocco also produce cork. A cork tree is harvested or stripped for the first time when it is 25 years old, and thereafter once every nine years.

To strip a cork tree is hard work. The cork oak bark is stripped into four foot planks. Once the bark is stripped off, it is left outdoors to season and dry for up to a year. After it has dried, the bark is then boiled or steamed to improve its elasticity and flatten it; then it is dried again. Finally the bark is trimmed into planks and separated according to quality. Wine corks are machine punched from the planks, graded according to surface appearance and conformity and then washed in a mild hydrogen peroxide solution to remove dust and to sanitize them.

Prior to 1995 most corks were washed in a chlorine solution. It is now known that chlorine can react with moisture and actually cause the growth of the fungus TCA.

Even though chlorine is no longer used in cleaning corks, the problem of corked wines has remained. TCA can be generated by a variety of things including cardboard cartons and wooden pallets. When it was first discovered the incidence of TCA in bottled wine was very high as much as ten percent. In the past 25 years the cork industry has made tremendous efforts to eliminate TCA. Now the estimates for TCA range from one to three percent but it is not possible to totally eliminate it.

The rise in TCA affected wines during the 1970s and 1980s inspired a group of winemakers in Australia to look for a better closure solution. Thus the metal screw cap or "Stelvin" closure was invented. This metal closure fits over the top of a wine bottle and actually seals out oxygen. There is a liner inside the cap made of tin sandwiched between two layers of nonreactive plastic. This has proven to be a very effective wine bottle closure. Today in Australia seven out of every ten bottles of wine use this screw cap closure rather than traditional cork. In New Zealand the number is even higher with nine out of every ten bottles of wine using screw caps. Screw cap use has spread globally. Today in North America almost 30 percent of the wine bottles use screw cap closures. It has been accepted by the wine industry that screw cap closures are very effective for young fruity white wines and red wines that do not need long term aging.

The research for alternative closures has also generated several other options. The synthetic cork is a plastic cork substitute that resembles a natural cork in color. It is made out of a nonreactive polymer. While this synthetic cork fits the same bottle as a natural cork its use is much more limited. Due to the fact that the polymer is oxygen penetrable it is only used for wines that will be consumed within six to twelve months of bottling. It is a very inexpensive closure option for the winery.

Other recent inventions include the ZORK. This unique, resealable closure was also invented in Australia but today is manufactured in North America. The ZORK closure utilizes similar sealing characteristics to the metal screw cap and is comparable in cost to natural cork. ZORK closures are becoming popular for use on red, rose and white wines at both bargain and premium price points. Another unique closure option is the Vino Lock which is made completely out of glass. This special glass closure requires a dedicated, unique type bottle and is a very expensive closure alternative, found only on super premium wines at present.

For long-term red wine aging the preferred closure is still natural cork. The corks used in more expensive bottles of red wine and some white wines are themselves very expensive costing upwards of a dollar each. Even using these expensive natural cork closures there is no guarantee that ultimately the wine in the bottle will not be affected by the dreaded TCA. In addition no one can predict how the wine in the bottle will actually taste after several years, due to the fact that natural corks are natural products; no two are exactly alike. Each bottle of wine, even when closed with cork from the same cork tree, may vary from bottle to bottle. Corks do not actually “breathe, “as was previously supposed. There are minute amounts of oxygen inside the cork cells themselves. This oxygen released into the wine in the bottle over time, is what ages the wine in the bottle and gives the wine complexity.

So next time you pull the cork, twist the screw cap , unZORK or pop open your “Best Bottle”, consider what goes in before the wine comes out.

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