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Quick tip: If wine smells like old, wet newspaper rather than fruit, it's probably "corked."

Winemaking techniques may be the same as they were 200 years ago, but how winemakers seal their bottles is changing. Sure, many wineries still use natural cork—over half of it supplied from Portugal, where, for generations, small-scale family farms have harvested cork-oak tree bark, a renewable resource, for the world's wine biz. But more and more wineries, from California to France to New Zealand, are adopting new methods: metal screw caps or synthetic cork-plastic aggregates. Why? A microscopic compound called 2,4,6-trichloroanisole (TCA), which forms when a fungus naturally found in the cork combines with chemicals produced during winemaking. The result is cork taint—a musty or dull taste that renders wine undrinkable. Experts estimate that up to 5 percent of bottled wine is tainted, or "corked."

Lauded for their ease, efficiency, and low cost, "screw caps are increasingly being used for wines that will be consumed young," says Bill Kremer of King Estate Winery in Eugene, Oregon.

But with wineries making the switch to synthetic alternatives that they hope will eliminate the risk of TCA damage, cork farmers are feeling the squeeze. Some have taken to planting eucalyptus, which grows quickly and can be harvested for eucalyptus oil every two to three years. (Cork is harvested every nine years.) And the World Wildlife Fund estimates that in the next decade, up to 75 percent of western Mediterranean cork forests could disappear, putting more than 62,000 jobs in danger.

Culture and tradition aren't the only things at stake, though. Environmentalists worry that if this farm conversion progresses, Mediterranean cork-forest natives, such as the Iberian imperial eagle and Iberian lynx, could face extinction.

But there's a solution: Drink more good wine. Some winemakers—Kremer, for one—maintain that traditional cork is the best and only way to properly age a wine.

If you choose to go for wines with natural corks, remember that wine should always have a fruity flavor. If it smells like old, wet newspaper, it's probably corked. "Most people can detect cork taint because that fruit character will be absent," says Peter Weber, director of the Cork Quality Council. "Just don't confuse cork taint with personal preference for flavor."