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Thursday, September 19, 2013

Did any wine writer actually read the PNAS TCA article?


So, the buzz in the wine writing world the past few days has been the "surprising new research" that suggested 2, 4, 6-trichloroanisole (TCA) doesn't actually smell like anything, let alone musty. The authors of the acclaimed study suggested that their data show TCA actually suppresses odors. Is that really new news? If you actually read the article (I conducted the arduous Google search for you...), you might come to a different conclusion than some of the people writing about the article.

I can't be the only person that knows low levels of TCA will kill a wine’s aroma and flavor. In fact, I know I'm not as Ray Isle wrote the last eleven words of the previous sentence over four years ago in Food & Wine. Yet, over the last couple days, Steve Heimoff, Wine Spectator and Decanter all wrote about the research seemingly without actually reading the paper.

If you read the article with a critical eye (I know, that's a pain to do sometimes...) you will see two things that should make you question all the lazy pundits. First, the study was conducted on newts (Cynops pyrrhogaster), not humans (Homo sapiens). They clearly stated, "functional olfactory receptor genes is different between amphibians and mammals, so we cannot rule out the expression of receptors with very high TCA sensitivity in humans." Hmmm. That changes the conclusion a bit. Human olfactory receptors could interact with TCA differently than those of newts! Additionally, the authors stated that, "we cannot assume that we surveyed all possible olfactory receptors in the newt." Might there be other olfactory receptors that transduct musty odors? Humans have around 400 functional genes coding for olfactory receptors. The picture just got a bit more complicated...

[note: the following paragraph was re-added after my original post was published to better reflect the full content of the PNAS study]

The authors did in fact conduct an experiment on on human perception of TCA (and TBA) in wine. They investigated the concentration levels at which "the reduction of original odor and the extrinsic musty smell from TCA were discriminated." So, in fact, the authors were able to show that humans do sense musty odors in wine caused by TCA and TBA. The levels varied person to person and the musty odor was recognizable in red wine at a lower concentration than white wine. So why the media blitz about an article that basically supports what we all knew about TCA? I know PNAS isn't hoping to increase its advertising levels! [end revision]

I don't have any answers to the question of why olfactory receptor cells removed from a decapitated newt did not trigger a musty odor, but I think the idea that this research is somehow earth-shattering is a bit hyperbolic. It is interesting to know how TCA (and don't forget the often neglected 2,4,6-tribromoanisole, or TBA) interacts with neurons, but to borrow something I saw in a tweet from my chemical engineering buddy Tom Mansell


7 comments:

  1. A wine writer (especially one for a major news or magazine outlet) actually read the scientific paper on which their story is based? You must still have been dreaming when you wrote the title to this post...

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  2. [Above 5:44 AM comment removed by the author to correct for a typo. Reposted below. -- Bob]

    Your editorializing on the Japanese TCA study leaves your blog readers with the false impression that they conducted “human-free testing" experiments.

    That's not how I read the report.

    Citing the sub-section headlined “Reduction of Wine Odors by TCA and TBA."

    “Effects of TCA on wine flavor have long been reported. However, previous surveys were conducted in the context of TCA contributing additional odors (1).

    In the present study, we showed that TCA suppressed the olfactory transduction current. Therefore, we reexamined human olfactory perception to look for reductions in wine odor.

    "In addition, we investigated the relative potency of odor reductions among TCA analogues or derivatives to compare against their CNG channel suppression properties (Channel Suppression by Related Substances and Correlation with Human Sensation).

    “Twenty panelists [ read: humans, NOT newts – Bob ] were asked to evaluate whether original odors of wines were reduced when they were contaminated by off-flavor substances.

    "For evaluation, the triangle test that has been approved in Japanese Industrial Standards (JIS) Committee or British Standards Institution (BSI)/International Organization for Standardization (ISO) was used.

    "The strongest reduction in odor was observed when wine was contaminated with TCA (Table 1). The off-flavor recognition thresholds were 47 pM (10 ppt) for red wine and 71 pM (15 ppt) for white wine. TBA also caused similar effects with slightly higher concentrations (290 pM for red and white wines; Table 1).

    "Reduction of odor perception was also observed with TCP at concentrations four "to five orders of magnitude higher (1.5 μM for red wine, 0.5 μM for white wine) than those of TCA or TBA (Table 1).

    “In another set of experiments, we also examined the concentration at which the musty odor of TCA was recognized in wine.

    "In evaluation with white wines, the reduction of original odor and the extrinsic musty smell from TCA were discriminated, and detected at approximately 2 to 4 ppt.

    "Thus, even when the panelists [ read: humans, NOT newts – Bob ] attended to different sensory parameters, the recognition threshold was almost the same between reduction of wine odor and addition of extrinsic odor .”

    If I am wrong about human test participants, please disabuse me of my ignorance.

    ~~ Bob

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  3. Bob, you are correct. I apologize that I gave impression that no human noses were harmed in the making of the study. The authors did conduct an addition experiment that used humans to sniff wine that contained TCA. In those panel evaluations, the musty odor of TCA was recognized in wine once concentrations reached a threshold. Below the recognition threshold, panelists did notice a reduction in odor. I found this part of the study to add no new data to the discourse other than support commonly held knowledge amongst people that are familiar with TCA in wine (see my quote of Ray Isle).

    I actually deleted a paragraph that discussed the panel experiments in the original draft of this post. I wish I had not, and though probably too late, have edited the post to better reflect your concerns.

    Thanks for taking the time to read and provide a thoughtful comment!

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  4. [PREFACE: I POSTED THIS ON STEVE HEIMOFF'S WINE BLOG.

    AS THERE IS NO GUARANTEE THAT THERE IS A HIGH CROSSOVER (I.E., "DUPLICATED") AUDIENCE BETWEEN STEVE'S READERS AND YOURS, LET ME TO PROFFER IT AGAIN HERE.]

    JAMES LAUBE AT WINE SPECTATOR HAS BEEN QUITE VOCAL AND PERSISTENT IN CALLING ATTENTION TO TCA IN DOMESTIC WINES.

    QUOTING THE MAGAZINE’S WEBSITE:

    “Wine Spectator’s Napa office has been tracking the number of ‘corky’ bottles in tastings of California wines since 2005, and the percentage of defective corks in that category has dropped from a high of 9.5 percent in 2007 to a low of 3.7 percent in 2012. The cork industry has a different estimate of cork failure: typically 1 percent to 2 percent.”

    [ Link: http://www.winespectator.com/webfeature/show/id/Wine-Flaws-Cork-Taint-and-TCA_3346 ]

    MORE RECENTLY:

    “The number of California wines flawed by apparent cork taint (2,4,6-trichloroanisole, otherwise known as TCA) fell in 2012 to its lowest level since we started informally tracking this controversial issue in 2005. Roughly 3.7 percent of the 3,269 cork-sealed wines from California that we tasted in the Wine Spectator office in 2012 were thought to be tainted by a bad cork. . . . That the percentage of TCA-tainted wines in 2012 is the lowest we’ve seen (down from 3.8 percent in 2011; the highest level coming in 2007 at 9.5 percent, or a 1-bottle-per-case average) . . .”

    [ Link: http://www.winespectator.com/blogs/show/id/47837 ]

    LAUBE CHAMPIONS THE USE OF A SPECIFIC TASTING GLASS WHEN CONDUCTING HIS WINE REVIEWS — NOTED FOR ITS ABILITY TO HEIGHTEN THE PERCEPTION OF TCA:

    Excerpt from Wine Spectator Online
    (posted February 22, 2005):

    “A Clear Benefit for Wine;
    Of all your wine paraphernalia, don’t overlook [wine] glasses
    – they really make a difference”

    [ Link: http://www.winespectator.com/webfeature/show/id/A-Clear-Benefit-for-Wine_2407 ]

    By James Laube

    . . .

    At home, I use Riedel and Spiegelau glasses (which you can easily order online), and to simplify matters I’ve narrowed it down to two — the Vinum Bordeaux and Vinum Chardonnay/Pinot Noir glasses. I’ve yet to find a table wine that didn’t perform well in one or the other.

    But at my office in Napa, for official Wine Spectator blind tastings, I use an old favorite. It’s not very pretty, but it’s effective. It’s a bowl-shaped, stemless glass with a small punt at the bottom, and an indentation for the thumb on the side. It’s called The Wine Taster Glass from a line of stemware known as Les Impitoyables. I always use this glass, and have for decades.

    As best I can remember, I learned about this glass in the early 1980s. . . . Many winemakers, in Bordeaux, Burgundy, the Rhone Valley and California . . . said they preferred it to other stemware because it helped highlight possible . . . flaws such as Brettanomyces, volatile acidity or TCA taint.

    . . . I’ve stuck with the Impitoyable because it has served me well. Part of it is habit and . . . a lot of it is a belief in the value of consistency, using the same glass for every wine, week in, week out.

    When you’re tasting wine, or better yet, critiquing it, you want to eliminate as many variables as possible. . . . you should go into every tasting . . . and . . . use the same glass.

    The Impitoyable . . . does highlight wine aromas better than any glass I’ve used. That’s why I’ve stuck with it for all these years.

    ROBERT PARKER LIKEWISE USES THE IMPITOYABLE TASTER GLASS WHEN CONDUCTING HIS REVIEWS.

    AVAILABLE FROM ONLINE WINE ACCESSORY SELLERS.

    ~~ BOB

    ("Full disclosure": I also use the Impitoyable Taster glass for critical wine buying decisions -- and have for 20 years.)

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