Cork is a renewable material — made from the fiber stripped from cork trees that can then regrow. The largest and most profitable use of this harvested cork worldwide is for wine stoppers.
Several environmental groups say the growing popularity of alternatives like screw caps is threatening Mediterranean cork forests, where cork is mainly grown. Cork oak covers about 6.7 million acres in the region and provides income for more than 100,000 people, according to the World Wildlife Fund.
Cork forests are predominantly privately owned, which puts them at greater risk for neglect or sale for development if the popularity of cork lessens.
Cork producers say they have seen the overall production of wine stoppers drop in the past decade. And last year, The World Wildlife Fund estimated that if winemakers continue their move away from cork, three-quarters of the western Mediterranean's cork oak forests could be lost within the decade, threatening jobs and ecosystems.
The Rainforest Alliance recently jumped into the fray, offering a certification system for wineries to verify that their cork comes from cork forests that meet the Forest Steward Council's social, economic and environmental standards — lending assurance to winemakers and consumers that the cork was properly handled.
The issue is complicated for winemakers, who are often swayed by issues of sustainability but have been burned by cork's quality issues in the past.
The primary problem that drove vintners away from cork was "tainting" or "corking." Cork taint is actually a chemical compound called TCA, which results from an interaction of mold, chlorine and other organic compounds that produce a moldy or musty smell and flavor that makes wine undrinkable.
Estimates vary, but some wineries say as much as 15 percent of their wine has been tainted in the past. Screw caps, by comparison, don't have issues with tainting and are a fraction of the cost. However, they are usually made from nonrenewable material — typically aluminum with a plastic insert. That also makes them difficult to recycle.