cork, Packaging, Research, sensory, sensory science, SOMM Journal, Wine
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Natural cork, a scapegoat for wine defects

When wine professionals encounter a sensory deviation in wine and the offending molecule isn’t obvious, cork often takes the blame by default. While not every taster is capable of decoding a library of aromas at the molecular level, the ability to detect basic defects like Brettanomyces, volatile acidity, and Trichloroanisole (TCA) is fundamental to objectively assessing wine quality.

During a recent sensory exercise conducted by Ana Cristina Lopes Cardoso, Research and Development Manager at Cork Supply Portugal, a group of trained tasters among them top Irish sommelier Julie Dupouy-Young and myself—were tasked with identifying TCA in wine at levels of 1, 2, and 4 parts per trillion (ppt/ng/l).

Lopes Cardoso staged a series of Duo-Trio tests in which one of three samples acts as the control to be matched. Not surprisingly, all the tasters could detect TCA, which has a very low threshold of 3–5 ppt—though very few tasters could find it at 1 or 2 ppt.

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Ana Cristina Lopes Cardoso, Research and Development Manager at Cork Supply Portugal, leads a sensory training.

Things got even more interesting when the tasters were also confronted with samples that had been heavily doctored with five different molecules that emulate TCA, including 1-Octen-3-ol, which smells distinctly of mushroom; geosmin, which is associated with the smell after a rainstorm; and 2,4,6-Trichlorophenol (TCP), a TCA precursor with a specific but hard to-detect chemical odor.

“For example, when analysis shows the presence pentachloroanisole (PCA) and TCA occurring together in wine, TCA is the source of the sensory deviation but cork isn’t the source of the contamination,” said Lopes Cardoso who points to winery hygiene, insecticides and building materials like insulation as the culprits.

Despite the existence of research identifying contamination molecules from production and storage premises for the past 25 years, it’s easy to see why cork takes the rap when other moldy or earthy-smelling molecules are present at detection thresholds: The majority of tasters simply can’t identify or differentiate between them. As the cork industry rushes to employ automated sensing equipment designed to weed out TCA-contaminated natural corks, it’s rare to find technologies currently available that screen for TCA and other “off-aromas.”

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Cork Supply President/founder Jochen Michalski and author.

According to Cork Supply President/founder Jochen Michalski, this makes the Northern California–based company’s service the most rigorous available in the marketplace today. During a process Cork Supply has developed called Dry Soak 100 (DS100), which analyzes the headspace of heated cork, natural corks are subject to a rigorous round of sensory evaluation by at least three human sensors. “Although we’ve also developed an automated technology to screen corks called DS100+, I still have more confidence in our human sensory DS100 screening method,” Michalski says. “With DS100 we’re also able to remove any other off-aromas.”

But it’s the latest research on corklins—compounds found in cork that react with flavonoids in wine to protect color and reduce astringency over time—that’s shifting the cork industry’s focus on sensory neutrality. Researchers are using near-infrared spectroscopy to grade corks and oak staves from low to high according to the amount of phenols they will release into wine. Given the cork industry’s speedy adoption rate of technologies that add value to their products, winemakers may soon have another criterion—phenolic content—to consider when selecting grades of cork.  See the SOMM Journal pdf – S&A Aug-Sept2018

8 Comments

  1. While there are certainly many taints possible in wine, I always suspect the cork for bottle to bottle variations.
    Despite all the propaganda from cork suppliers, none offer a guarantee I would consider; I.e. TCA less than %1 by my tasting panel, confirmed by independent laboratory, they buy 100% of any batch of wine that fails.
    I wouldn’t buy bottles if 5-8% tainted my wines.
    Zero TCA issues with Nomacorc. And a zero carbon footprint.
    Paul Vandenberg
    Paradisos del Sol
    A Zero Pesticide Vineyard

    • deborahparkerwong says

      Paul, I didn’t get in to discussing the guarantees that are being offered by the cork producers because that’s not the point I wanted to make. It looks like a key quote was edited from the article that inspired me to write in the first place, “For example, when analysis shows the presence pentachloroanisole (PCA) and TCA occurring together in wine, TCA is the source of the sensory deviation but cork isn’t the source of the contamination,” said Lopes Cardoso who points to winery hygiene, insecticides and building materials like insulation as the culprits. Similarly, the TCA-like molecules TBA and TeCA do not originate in wine.

      • Paul Vandenberg says

        I can’t argue that bit, but I’ve never experienced an entire lot of wine with perceptible TCA.
        With bottle to bottle variation I suspect the cork.

  2. Jeff Hinchliffe says

    I am not seeing any support in the article itself for the scapegoat claim in the headline.

    • deborahparkerwong says

      Hi Jeff, My point is that there are many offending molecules that do not originate from cork that contribute to sensory deviation. An importanat quote was edited from the article that further supports my point: “For example, when analysis shows the presence pentachloroanisole (PCA) and TCA occurring together in wine, TCA is the source of the sensory deviation but cork isn’t the source of the contamination,” said Lopes Cardoso who points to winery hygiene, insecticides and building materials like insulation as the culprits. Similarly, the TCA-like molecules TBA and TeCA do not originate in wine. I hope this addresses your question.

  3. Oliver McCrum says

    Hi Deborah,

    With respect, this sounds like a PR distraction offensive from the cork industry, which is not ‘The Scapegoat for Wine Defects’ but the actual cause of most Wine defects. As has been pointed out above, anything occurring in the wine would be a batch problem, readily identifiable, quite different from the bottle problems caused by most defective corks.

    Separately, I’m curious about those thresholds you quote; in my office our threshold is somewhere between 0.5 and 1.0 ppt, much lower than those you quote.

    • deborahparkerwong says

      Hi Oliver, This was a technical sensory training session not unlike the dozens of sensory training sessions I’ve attended over the years and clearly not intended as a PR stunt. There are scenarios that point to batch problems with molecules that emulate cork and unless you have a second bottle handy to compare, the taster would never know the difference. When we encounter sensory deviations/defects that point to cork or are cork like during a wine competition, we’ll call for a second bottle and very frequently find the same sensory deviation in the second bottle. A bad batch of corks or a bad batch of wine? My interest here is gaining a greater understanding of the molecules that masquerade as TCA knowing full well that cork can certainly be defective.

      The thresholds used in the sensory trial were established by Ana Lopes Cardoso and I reported on what the tasters in that group of international wine press experienced. Only a few were able to detect TCA below 1 ppt. I would say that your team really has a nose for detecting TCA.

  4. Oliver McCrum says

    Hi Deborah,

    With respect, I can’t say what their motivation was but the result is pure PR benefit. Until they demonstrate how many wines are affected by these other chemicals it’s pretty dubious that this ‘scapegoating’ is a real problem.

    We have had a number of bad batches of agglomerates in the last few years that are consistently corked at a fairly low level, which gives us a sense of our thresholds. We had a batch of dry white wine that was all at 1.0 or so and a number of our customers picked it up, not just the beagles I work with.

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