With a new initiative from the California Wine Club (CWC), you can earn credit toward your next wine purchase while helping the environment. In partnership with ReCORK, the CWC will plant 1,000 new cork trees if they collect 20 million corks by September 2011. For every 30 corks that you mail in, you’ll earn a $10 credit towards purchases from the club and entry into a variety of weekly contests.

This initiative got me thinking about corks. Cork has been used to stopper wine vessels for centuries, though it faces growing competition from other closure methods. But why do we use cork? How are corks even made?

Learn more about cork and its history below the fold.

The majority of the cork used to plug wine bottles is harvested from Cork Oak trees native to southwestern Europe and northwestern Africa. Over 50 percent of the cork that’s harvested worldwide each year comes from Portugal and nearly 30 percent is from Spain. Portugal-based Amorim, the company behind ReCORK, is the world’s leading cork producer.

Skilled workers harvest cork by stripping the tree’s outer layers of bark using specialized tools and a technique that allows the tree to recover and continue growing. Cork may be extracted from a tree approximately every ten years, and each tree lives for about 200 years. Only the highest-quality cork is used for wine stoppers – the rest is manufactured into building materials, shoes, and other products.

Uploaded to flickr by Josep Ma. Rosell.

Several steps are now in place to prevent TCA taint in the cork. Once harvested, the cork bark is boiled and treated to extract any impurities. Cork from the bottom of the tree, which is more prone to contamination, is no longer used for wine stoppers. The sheets of bark are then punched into stoppers and steam-treated to further purify them. Finally, the stoppers are polished into shape and sterilized with hydrogen peroxide.

The cork particulate left over after the stoppers are punched is used to make technical corks. Technical corks composed of reconstituted cork granules are used mainly for sparkling or early-drinking wines.

The first modern use of cork to close bottles of wine, however, is attributed to the 17^th century French monk Dom Pérignon, who substituted cork for the more commonly used wooden stoppers wrapped in olive oil-soaked hemp. The cork proved far less likely to pop out, leading to its adoption by vintners throughout Europe. Historically, cork was used by many ancient societies including the Egyptians, Greeks, and Romans to stopper vessels containing olive oil, wine, etc.

It’s a common misconception that cork trees are endangered today.

In part, this misconception is due to the emergence of synthetic stoppers and screwtop bottles over the past two decades. But these other closure methods arose largely in response to a widespread increase in TCA-tainted cork during the late 1980s and 1990s. About ten years ago, Wine Enthusiast estimated that as many as 5-10 percent of all bottles suffered from TCA taint — and high-end wines weren’t immune.

While the cork industry has been able to nearly eliminate the problem through more sterile production, it will be difficult for the industry to reclaim the market share captured by these other closures.

Every closure method affects a wine’s taste differently, and the debate over which is best has been quite contentious. Synthetic wine corks have gained popularity due to their low cost and reliable quality. However, they are prone to getting stuck in the bottle after a few years and some studies have suggested that they are too permeable to oxygen, preventing some reds from aging correctly. Screwcaps and bottle tops suffer from the opposite problem – they allow no oxygen into the bottle, but some O₂ is required to keep sulfide levels under control. Despite their drawbacks, both methods are widespread among early-drinking wines and will likely grow more common as their producers address quality issues.

Uploaded to flickr by Francois Schnell.

Recently, cork producers have begun to emphasize their role in promoting biodiversity and protecting the environment. Unlike synthetic stoppers or bottle caps, cork is a renewable, recyclable, and biodegradable resource. In addition, the industry claims that their sustainable farming methods provide  a protected habitat for several endangered species, prevent desertification and soil erosion, and help maintain watersheds. Even the World Wildlife Fund has gotten on board with a cork conservation campaign.

Though the environmental claims may be somewhat overstated, there is no doubt that the majority of wine purists still insist that cork provides the best closure option for high-quality bottles.

Take advantage of the fact that the majority of bottles still have natural cork stoppers by sending yours in to the California Wine Club and receiving that $10 credit. More information on is available on their website, www.cawineclub.com.