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Chemical Sensing

Tales of the fungus among us

by Marc S. Reisch
September 8, 2019 | APPEARED IN VOLUME 97, ISSUE 35

 

A real corker

09735-newscripts-corkcxd.jpg
Credit: Shutterstock
Barking up the wrong tree: Gas chromatography may yet save wine lovers from cork taint.

Is your wine corky? Does it smell like a wet dog and have a flat, dull flavor? If so, you’ve become a victim of cork taint. A collaboration between a maker of natural cork bottle stoppers and an expert in gas chromatography hopes to banish the problem for good.

The contaminant that turns good wine into sour grapes is 2,4,6-trichloroanisole (TCA), a compound produced by mold. Although cork taint is a centuries-old problem, scientists have identified the culprit only in the past 40 years. TCA gets into cork through an age-old battle of the kingdoms: Plantae versus Fungi.

Cork is the bark of the cork oak tree, also known as Quercus suber. Once every 10 years or so, the trees are stripped of their bark. Over a 200-year lifetime, each bark-regenerating tree can provide thousands of wine stoppers.

Q. suber defends itself against fungal attack by producing phenolic compounds. The fungi defend themselves in turn by methylating the phenolics into less toxic compounds, such as anisole. TCA is generated when anisole reacts with chlorine in the environment or when the bark is treated with a chlorinated antimicrobial compound (Appl. Environ. Microbiol. 2002, DOI: 10.1128/aem.68.12.5860-5869.2002). Estimates are that 1–7% of wine is tainted.

So far, at least, no one has found a way to remove TCA from cork. Better cork cleaning and processing have minimized the problem, but short of going to plastic or screw-on aluminum caps, both of which many respectable wine lovers eschew, no one has found a surefire way to guarantee that each and every cork is TCA-free.

Enter Amorim, Portugal’s largest cork supplier. The company sought out gas chromatography expert Ellutia, and together they have developed the NDtech, a custom system that can test individual stoppers for the malodorous meddler.

Winemakers, Amorim says, can use “the supreme guardian for wine” knowing that if any TCA is in the cork at all, it’s at a level low enough to preserve the wine’s bouquet. The guarantee came at a cost: more than $11 million went into the design and development of the system, Amorim says.

Andrew James, Ellutia’s marketing director, says years of research went into reaching the necessary analytical detection limit, a mere 0.5 ng/L. The first prototype in 2011 could detect any cork with more than 5 ng/L. In 2015, Ellutia installed the first commercial testing line for Amorim, where 60 gas chromatographs now ferret out wine-ruining corks. Rejected corks—those with 0.5 ng/L or more­—go to other uses, such as for flooring or gaskets.

During a day’s testing, each sniffer can test 34,650 corks a week. That’s a rate of 1 cork every 16 s, James says. The real corker will be if Amorim can achieve its testing goal of 1 every 10 s, or more than 3.3 million a week.

 

Mushrooms on steroids

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Credit: American Truffle Company
Truffles: Nothing to trifle with, and they sell for as much as $2,600 per kilogram.

Aside from gas chromatographs, dogs are pretty good sniffers, too, especially when searching for Périgord black truffles (Tuber melanosporum) in unusual places.

Thanks to Bella the border collie, folks at the Otellini Truffle Orchard in California are claiming they are the first to succeed in using a scientific approach to grow the European delicacy in the US. The American Truffle Company, which is building an empire of partnerships with US truffle orchards, says it inoculated with black truffle fungus the Otellini orchard tree where Bella found the lusty subterranean growth.

Cultivation according to “strict scientific protocols” sensitive to the orchard’s microclimate and soil conditions accounts for the resounding success, the company says.

The specimen that Bella dug up in December weighs 108 g. Typically, Périgord truffles weigh between 30 and 60 g. At current prices, Bella’s find is worth about $285, a thousand times as much as a wine bottle cork stopper.

Marc Reisch wrote this week’s column. Please send comments and suggestions to newscripts@acs.org.

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