Wine Bottle Stoppers: Natural Cork, Synthetic or Screw Top?
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Wine Bottle Stoppers: Natural Cork, Synthetic or Screw Top?

Lisbon : Portugal | Sep 28, 2011 at 3:51 PM PDT
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100% Cork: Allen Hershkowitz of the NRDC Discusses Benefits of Real Cork

September 28, 2011--

In recent years there has been a lot of discussion about the introduction of synthetic corks and screw tops for wine bottles. Which kind is best, or does it matter? Change is usually troubling, and deciding on one’s preference for wine bottle stoppers is a dilemma we will be forced to confront at Ye’ Ole Bottle Shop.

Natural cork has been used since the ancient Greeks and Romans used cork in combination with natural resins to stopper wine and oil amphorae. Now, some 70 percent of all cork produced is used to make wine bottle stoppers. Portugal alone makes 40 million stoppers per day.

Cork is made from the bark of a cork oak tree and the predominant tree species is in Portugal and accounts for a little more than half of the world’s cork output, producing 157,000 tons annually. There are also some groves in France, Spain, Italy, Algeria, Morocco and Tunisia. It is an industry where over 100,000 people depend on cork growing and processing in these countries for their livelihood.

Harvesting Cork Bark

The bark is harvested for the first time when the tree is 25 years old. Then it is removed every 9-12 years without ever damaging the tree, which lives around 200 years. Cork obtains the qualities needed for the production of wine bottle stoppers -- its main application -- only after the third harvesting. This process is costly in time and effort keeping in mind that it’s an age old tradition in wine making.

Natural cork’s breathability is its primary allure. After bottling, the wine can age in the bottle because of the oxygen exchange through the cork. In recent years the use of natural corks as been challenged and resulted in studies measuring the oxygen exchange comparing natural cork, synthetic and screw tops because some vintners wanted to address cork tainting as well as possibly the economic aspect of sealing bottles.

Why some vintners are switching from cork to plastic

Some believe synthetic corks are a great way to store wine, and keep it from developing faults over time. Traditional cork, which comes from cork trees in Portugal, Spain, and other parts of the Mediterranean, can harbor a fungus called 2,4,6-trichloroanisole (aka TCA), which causes musty odors and flavors in wine (aka cork taint). Some estimates claim that every one in twenty bottles with natural cork is affected bFungus doesn’t grow in synthetic cork or screw caps and synthetic corks make long-term storage of your wines without the fear of cork taint.

Argument Against Using Plastic Corks

The argument against using plastic appeared in National Geographic in 2002:

“Vintners using plastic stoppers in their bottles may have an unanticipated impact on wildlife. Spain and Portugal grow more than three million acres (one million hectares) of cork oaks, used in the production of traditional stoppers for wine bottles. For centuries cork farmers have tended the trees, harvesting the bark about every nine years. Seldom disturbed, wildlife living in and among the trees have been left to flourish. But conservationists now worry that the increased use of plastic, replacing cork in more than five percent of wine bottles, may depress the cork market and force farmers to clear the trees in favor of other, more profitable, but more disruptive, crops. To boost awareness, they propose that bottle labels indicate the type of stopper or that the wrapping from bottle tops be omitted.”

Wine blogging sites lament how hard the plastic corks are compared to natural corks wishing vintners would use cork, not plastic for stoppers. Some state they have broken their wine bottle openers while trying to open a bottle with a plastic cork. (I have personal experience with this and agree completely.)

Screw Tops

Screw caps or "Stelvin caps" are closures made from aluminum material that threads onto the bottleneck. They are the predominant closure used by New Zealand wineries. New Zealand vintners claim screw caps form a tighter seal and can keep out oxygen for a longer time than cork. These benefits aid in maintaining the wine's overall quality and aging potential. Michel Laroche of Domaine Laroche noted that this played a role in his decision to adopt screwcaps. "Extensive quality tests show convincing results: apart from protecting against cork taint, screwcaps are also beneficial in the aging of wine, particularly preserving the aromatic freshness.”

Food and Wine Magazine confirms that some producers, like Australian star Jeffrey Grosset, have spent years studying the subject. Grosset has been analyzing the effects of TCA (cork taint) and considering alternatives to corks for 25 years. As of this year, almost all (92 percent) of Grosset's wines will be bottled under screw caps—even his priciest: a $43 Pinot Noir. He has also traveled around, talking to other winemakers about what he's learned. In New Zealand, several producers were convinced to follow suit, bottling all of their wines with screw caps.

The Question of Oxygenation

A University of Bordeaux study on Oxygen Movement through the different types of stoppers in Wine Business.com confirms what wine makers have long thought: corks allow a tiny amount of oxygen to enter the bottle of wine allowing the wine to age in the bottle. What they also discovered is oxygen enters the wine through plastic corks as well. Natural corks, however, oxygenate less over time.

There were higher rates of oxygen permeation with synthetic stoppers and lower oxygen rates with screw tops and natural cork fell in between in terms of ingress of oxygen after bottling.

The Bordeaux team has now published the results of three years of their measurements, comparing the oxygen transmission rates (OTRs) of cork stoppers with synthetic stoppers and screw caps. A summary appears in the July/August 2007 Practical Winery & Vineyard (PWV).

Because cork will slowly allow very small amounts of oxygen into the wine after bottling, it has long been held that this property helps the wine to develop and age gracefully. In the past, researchers have not had a reliable method for measuring the amount of oxygen that enters the wine after bottling or for comparing different types of closures. The New Zealand vintners, on the other hand, believe synthetic corks also allow for “graceful aging.”

This is probably not a decision you will have to make soon, but arming yourself with correct information is the best place to start any new adventure—even when going to Ye Ole Bottle Shop to search for the perfect bottle of wine.

From Omar Khayyam:

A Book of Verses underneath the Bough,

A Jug of Wine, a Loaf of Bread-and Thou

Beside me singing in the Wilderness-

O, Wilderness were Paradise now!

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Corks
100,000 people depend on the natural cork industry for their livlihood.
Dava Castillo is based in Clearlake, California, United States of America, and is an Anchor on Allvoices.
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