The Incredible Cork

By Posted on Nov 26 2009 | By

Take a guess. How many air cells in one wine cork? A thousand? Ten Thousand? A million?

Let’s just round out the number at 800 million.

corksIndeed, 800 million, fourteen-sided air cells are contained in each cork used to seal a wine bottle. And that’s only the beginning of the marvelous attributes of a closure that has been in use for over three hundred years.

The first person to observe air cells in a cork was Robert Hooke, the English inventor of the microscope. Around 1662, taking a thin slice of cork, he slipped it under the lens of his new 50x magnification instrument. “I could exceeding plainly perceive it to be all perforated and porous, much like a honeycomb,” he later recorded. He was so struck by the design he called the tiny structures “cells” because they reminded him of the small monastery rooms that monks slept in. Science later adopted the term and to this day it is the conventional description of the smallest structural and functional unit of an organism.

While cork has been used for various purposes for centuries, its serious application as a wine bottle stopper emerged in the early 1700s. It was a technology so inventive and effective it is still the primary method of protecting wine from the effects of oxidation.

One of the key attributes of cork is its compressibility. It reacts like a sponge when placed under pressure, springing back to 90 percent of its normal size within a day. One can easily observe this characteristic by taking a cork that has been removed from a bottle and setting it aside for a few days, and then trying to reinsert it back into the vessel. It simply will not fit.

When punched cut into a wine cork and inserted in a bottle, it instantly expands and grips the sides of the glass in an almost—but not quite—airtight seal. The discovery of this unique trait allowed wine to age for more than a year, the single most important advancement in the history of wine production.

Cork Oak Tree Bark

Cork Oak Tree Bark

Cork is produced from the bark of the cork oak tree, Quercus Suber. Eighty percent of the world’s cork is produced in Spain and Portugal, with remaining forests located in Italy and North Africa.

Over eons the tree has evolved two sets of bark, one living and one dead. It is the outer dead bark that is harvested and used for commercial purposes. This unique double bark trait is believed to be evolutionally in origin. The tree thrives in sandy soil and a climate with little rainfall. Periodic forest fires forced the tree to develop a protective outer bark that can be damaged—or stripped off—without killing the tree. Once again, nature displays its cleverness by creating a useful survival mechanism.

Stripped Cork Oak Tree

Stripped Cork Oak Tree

The harvesting of cork follows a strict law enforced pattern. For the first twenty-five years, the trees cannot be touched at all. When the first bark harvest occurs, the product is low grade and unusable for wine corks. Another nine years must pass before the second harvest takes place. Yet again, the quality of the bark is not high enough for use as a closure. It’s only at the third harvest that the stripped bark can produce high quality corks. Thus, a tree will be approaching fifty years of age before its product becomes commercially viable for the wine industry.

But being patient has its dividends. The cork oak tree has a life expectancy of 150 to 200 years, generating up to 17 harvests. An impressive example of the production capability of these trees is the Whistler Tree in Portugal. The tree derives its name from the countless songbirds populating its branches. It has been producing cork every nine years since 1820 and will be harvested again in 2010. With its next bark stripping, this ancient beauty will have produced over one million corks.

Cork bark is hand harvested by skilled workers. The bark must be cut so as to not injure the under layer of living bark. Workers use four-foot long, fan-like axes to cut and strip the bark in sheets several yards long and a few yards wide. It under goes sorting by quality and air seasoning for six months. It is then boiled, sliced, punched and sorted by grade. Finally, the corks are polished, a thin film of paraffin applied and bagged with sulfur dioxide gas to protect them from spoilage prior to the bottling process.

Because of a growing problem in the 1980s with “cork taint”—a fungus that can contaminate wine with a musty aroma and mute its flavors—the leading manufacturers are increasingly using additional proprietary treatments to eliminate such contamination. The rise of this plight is what precipitated the creation of the screw cap phenomenon worldwide. Cork producers are now claiming the problem is under control.

Just as pork producers claim every part of a hog is used except its squeal, so it is with cork. Any remaining cork from the production process—called “blocker waste”— is granulated and used in a wide variety of products; including gaskets, tiles, bulletin boards, fishing rod handles and decorative items. Cork has even been used in the nose of the NASA space shuttle.

corksFor many wine lovers, the romance of enjoying wine is closely linked to the use of a cork to seal the bottle. The scene of a waiter approaching a dining table, presenting the wine and then quickly snapping open a screw cap seems somehow a bit too modern for their taste. It’s not often one encounters a technology in use today that was first introduced over 300 years ago. But perhaps within the next decade, the future—or demise—of the natural cork closure will be resolved by the power of the marketplace.

Nonetheless, there are legions of wine lovers who do not want to toss their beloved wine openers away. Their fervent hope is the next generation of enophiles will not be buying corkscrews in antique shops.

May the cork live long and prosper.











  Published in the 2009 Winter edition of the Virginia Wine Gazette.

Categories : WINE ARTICLES