One of my favorite sounds is the "pop" that happens when a cork makes its way out of a bottle of wine. Of course, the loud pop from a bottle of sparkling wine is the most fun, but I even enjoy the softer pop from a bottle of still wine.

Corks have been used as wine closures for hundreds of years, but natural cork is no longer the only option for sealing a bottle of wine. Screw caps, synthetic cork, Zork (a peel-away stopper), and glass stoppers called Vinolok all have a share of the market, but natural cork is still the most-used closure, and with recent improvements in cork quality, it's taking back a small portion of the market it lost.

Reducing cork taint

drinking wine If your wine smells like wet cardboard, chances are it's been tainted with TCA. (Photo: Goodluz/Shutterstock)

Cork taint is caused by the presence of the chemical 2,4,6-trichloroanisole, or TCA, in the cork. You'll definitely know if a wine is "corked" if it smells like wet cardboard or newspapers. Not all corked wines have this smell, though. If the levels of TCA are very low, the wine won't smell like wet cardboard, but it will be dull, lacking in aroma and flavor. This leaves the wine drinker thinking something is inherently wrong with the wine without realizing it's the TCA that's the problem. A corked wine is not harmful to drink, but it is unpleasant.

Over the past decade or so, the wine cork industry has worked to drastically reduce the number of TCA-tainted corks that end up in wine. Several companies are now testing corks in a non-destructive way, and fewer and fewer tainted corks are ending up in wine.

"Through a combination of better forestry practices and better preparation of the wood, we have TCA down to a level where it's not really common at all," said said Peter Weber, Executive Director of the Cork Quality Council.

"Producers are making sure there is no chlorine being used in the forest," he said, "Everybody now knows to try keep chlorine down because it's a precursor to TCA." Residual chlorine from insecticides can come in contact with the wood, but the practice of using these insecticides stopped in the 1990s in many cork forests.

Harvest management is also important to reducing cork taint.

"When they do the harvesting, they now do a better job of leaving bark that is close to the ground on the tree," said Weber. "If there is TCA, it would be stronger where there is earth contact. Basically, they leave 6 to 7 inches on the bottom."

Once the wine corks are created, new testing procedures are implemented to test.

"The industry developed a way to detect TCA by gas chromatography," said Weber. This method analyzes wines that have had corks soaking in them for 24 hours for the presence of TCA. If an unacceptable level of TCA is identified, the corks are rejected.

"What we find now is virtually most everything we get is below reporting levels," he said. "It used be that we were getting levels of 2 parts per trillion. The average is now 1 part per trillion." At these low levels, the TCA should not affect the wine.

Growth of cork

cork oak trees Cork is harvested from the barks of trees. (Photo: Antonio/flickr)

Because of the improvements in the quality of wine corks available, Weber says there has been a significant increase in the use of cork over the past seven years.

Richie Allen, director of Viticulture and Winemaking at Rombauer Vineyards in St. Helena, California, is confident enough in the quality of cork that he uses it for about 95 percent of the winery's bottles.

"The cork industry managed to get TCA levels down over the last 15 years," he said. "What has really changed in the past two years, though, is technology — the ability to screen corks individually. Rather than doing batch screening, a lot of companies offer individually screened corks for TCA."

And, although the screening isn't 100 percent perfect, it's good enough that by next year, Allen intends to have all Rombauer's wines under cork even though the corks that are screened are more expensive, about 15 cents extra per cork.

The added expense is a prudent investment, according to Allen. By virtually ensuring no one will have a bad experience because of cork taint, the winery is likely to sell more wine.

"When you look at it from a product value standpoint," he said, "you need to look at it by the number of people who are going to try our wine for the first time and have a bad experience."

Another reason Allen is a supporter of cork is the sustainability of cork forests.

"If the cork industry went away," he said, "Portugal would lose vast amounts of sustainable forests."

Preserving the cork forests

cork forest The bark from the cork trees will grow back and be available to harvest again in nine years. (Photo: Robin Nieuwenkamp/Shutterstock)

There's a lot of consumer confusion about cork forests and how cork is harvested.

"No one in America knows anything about cork," said Patrick Spencer of Cork ReHarvest, a nonprofit that recycles wine corks.

"Cork is only one of the two tress that you can take the bark off and not harm the tree," said Spencer. "Yet, people are told over and over that trees are being cut down and there is a cork shortage."

In a poll, Spencer says that 80 percent of the people asked did not know that cork trees are don't get cut down to harvest the cork. The cork comes from the bark of the tree, which grows back and is able to be harvested every 9 years.

The 6.6 million acres of cork forests are integral to environmental sustainability in the regions they grow. These sturdy forests are important in reducing erosion. Cork Quality Council's Weber says they are the last defense between desertification in parts of North Africa. Cork forests also have a high level of biodiversity, second only the the Amazonian Rainforest.

The trees are great sequesters of carbon, too. Cork trees store carbon in order to help their bark grow, according to the Cork Forest Conservation Alliance. A harvested cork tree stores up to five times the amount of carbon than a non-harvested tree.

"The World Wildlife Fund considers cork forest to the most crucial habitat in Europe," said Weber.

The environmental importance of the cork forest is enough of a reason to continue to support the wine cork industry, but the tradition of using cork to close wine bottles gives winemakers another reason to choose it.

Tradition reigns

opening wine corkscrew There's a lot of tradition and romance associated with wine corks. (Photo: LightField Studios/Shutterstock)

The tradition and the romance of using corks for fine wine often leaves consumers with the impression that any wine under cork is a better quality than a wine under an alternative closure.

"From my standpoint, expensive wines — limited production, luxury wines — are sealed with cork," said Rombauer's Allen. "It has to be high quality to go in the highest quality items in the world. If the top producers are using because it's the best available, I figure I'm going to have the best quality in my wines, too."

Allen believes in the old adage "the customer is always right."

"In America and Europe," he said, "people definitely have a preference and perception that cork is highest quality and what seals a fine wine."

Cork Quality Council's Weber says that a few years ago they did a survey and found that 93 percent of people had the perception that cork was a higher quality than other closures. They've found that American wine drinkers believe that wine under cork is a higher quality, and winemakers believe wine under cork tastes better.

And, while our perceptions about the quality of wine under cork may not be accurate — there are plenty of quality wines under alternative closures — the vast majority of wines over $15 made in America use cork. Americans don't want to pay a lot of money for wine under other closures.

Recycling wine corks

corks Don't let those corks pile up for too long. Recycle them. (Photo: Arty Om/Shutterstock)

"It's a considerable amount we've removed from landfills," said Spencer.

Although Cork ReHarvest recycles the corks — and that's a good thing — its main goal isn't necessarily recycling. It's education. Each recycling bin it has placed with its partners has five bullet points that educate consumers about the fact that cork trees are not destroyed when cork is harvested and that cork forests are vital to environmental sustainability.

You can locate a Cork ReHarvest dropbox on the organization's website.

Another company that recycles corks is Recork. It collects corks and turns them into comfortable shoe insoles. Recork was adopted by the company Sole in 2008 in order to weave sustainability into its business model.

It may seem that since cork is natural and breaks down in landfills, and the preservation of cork forests is so important, that recycling corks could be counterproductive to keeping those forests necessary. However, corks sequester a lot of carbon, and by recycling them, that carbon stays contained.

"There are 13 billion cork stoppers produced every year," said Pia Dargani, Program Director for Recork. "If all of them are thrown in the garbage and end up in a landfill, they will release the carbon dioxide that they've held over the years as they break down."

But, by grinding the wine corks up and recycling them, the little particles they are ground into hold on to that carbon.

"A lot of people tend to hoard cork at home by keeping them in jars," said Dargani. But. she encourages people to recycle them.

"Cork stoppers are amazing," said Dargani. "We can really give cork a second life."

You can find a Recork drop off location on the company's website.

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.