HAC(k)ing a Wine, The New Science Of Cork Taint

Ξ December 5th, 2010 | → 18 Comments | ∇ A Day at a Time, Technology, Wine News, Wineries |

For many years now since the discovery of 2,4,6-trichloroanisole (TCA), whenever one encountered a wine exhibiting a moldy basement and wet dog nose, and fruit muted or altogether absent, with a shortened finish on the palate, one said the wine was ‘corked’. A cliché fixed in the popular imagination, the term ‘corked’ naturally has led the uninitiated and the expert alike to believe only corks are responsible for this specific constellation of descriptors. But this is a very small part of the story and, more importantly, only partially correct. Recent scientific studies have revealed other active agents — along with TCA, all haloanisoles — are also directly responsible for the fault. And among the agents most deserving of our critical attention is 2,4,6-tribromoanisole (TBA). It is for this reason I am here proposing the replacement of the term ‘cork taint’ for HAC or HAlonasiole Contamination. In this computer-savvy era, it is hoped that we might now begin to refer not to a corked wine, but to a HAC(k)ed wine. Let me try to explain.
 
What is TBA? From the 3rd edition of Dr. Ron Jaskson’s Wine Science:
 
“The absence of detectable TCA in some wines identified as possessing a corked odor may relate to newly discovered musty-smelling compounds. Chatonnet et al. (2004) have isolated 2,4,6-tribromoanisole (TBA) from several corked wines in France. TBA appears to have a similar microbial origin as TCA – methylation of its halophenol precursor, TBP (2,4,6-tribromophenol). The latter is often used as a fire-retardant and wood preservative. As a consequence, it may be found on wooden or wood-based material throughout a winery. The common mold, Trichoderma longibrachantum, possesses an o-methyltransferase that can methylate phenols containing fluoro-, chloro- and bromo-substituents (Coque et al., 2003). The conversion of TBP to TBA generates a highly volatile compound (easily contaminating a wine cellar). It adsorbs efficiently into hydrophobic products such as cork, polyethylene, and silicone. Thus, both natural and synthetic corks, the polyethylene liners of screw caps, silicone bungs of barrels, vulcanized rubber gaskets, and polyethylene- or polyester-based winemaking equipment may adsorb significant amounts of TBA. It can subsequently be desorbed into wine. TBA has an extremely low detection threshold, similar to that of TCA (parts per trillion).”
 
For our purposes the “methylation of its halophenol precursor” describes a biological defense mechanism used by wide spread, commonly encountered filamentous fungi (but also some actinomycetes, Streptomyces, for example) when in the presence of specific environmental toxins. The fungus secretes an enzyme, chlorophenol O-methyltransferase (CPOMT), which essentially transforms the bio-toxin into a harmless substance. This is what occurs in the formation of TCA when the environmental precursor, 2,4,6-trichlorophenol (TCP) is transformed into the biologically harmless TCA.
 
Now, TCA and TBA precursors have long been used as fungicides, but also as general pesticides, as wood preservatives; they are mixed in fire-retardant paints, and, in fact, are among the most persistent environmental pollutants. Called halophenols, the precursors of TCA and TBA are a chlorophenol and a bromophenol respectively. (The prefix ‘halo’ merely refers to the position on the Periodic Table of the Halogens: Chlorine, Bromine, Flourine, Iodine, and Astatine.) And it is here the story takes a decisive turn. Just as the biological activity of a microorganism transform the environmental toxic 2,4,6-trichlophenol (TCP) into the harmless, yet wine fouling 2,4,6-trichloranisole (TCA), so does a microorganism transform the toxic 2,4,6-tribromophenol (TBP) into harmless, yet wine fouling 2,4,6-tribromoanisole (TBA). (Each of these halophenols are then said to have become haloanisoles.) It may therefore be said that these specific halonisoles of Chlorine and Bromine, TCA and TBA respectively, are two of the agents responsible for ‘cork taint’. (Other agents: PCA, 2,3,4,6TeCP, are beyond the scope on this gloss.) Yet cork is not the ’source’ in any conventional sense.
 
When one speaks of a ‘corked’ wine, one is referring to TCA only if a scientific assay has determined its specific presence. As is well known, the cork industry has discontinued the practice of using hypochlorite-bleaching of cork stoppers for many years. It was this practice that led directly to the formation of the haloanisole TCA. Yet ‘corked’ bottles, sadly, continue to be discovered. After all, the tasting threshold of TCA is estimated to be around 2 to 6 parts per trillion, a bit higher for TBA. This translates into roughly 2 to 6 sugar cubes dissolved in a quantity of water equal to 100 Olympic-sized swimming pools! So, inasmuch as the industry is dealing with a compound active in nano-grams, the universal recognition of the reduction of ‘cork taint’ testifies to the remarkable success of new technologies and practices.
 
Yet new scientific research clearly demonstrates that cork, in addition to being a potential originating source of TCA upon leaving a factory, it also readily absorbs TCA from any number of environments. And a cork stopper may also absorb TBA. But not only cork stoppers. Plastic stoppers and the liners of screw caps (see below) also readily absorb the offending molecules. Indeed, wine itself may become tainted before it is sealed with any closure. And this is why. From a 2008 Practical Vineyard and Winery article, “2,4,6-TBA, The Next “2,4,6-TCA” of the Wine Industry”,
 
“Like 2,4,6-TCA, 2,4,6-TBA causes a musty, mold taint in wine at very low concentrations, but it has the potential to be an even more serious problem to the U.S. wine industry because its precursor (2,4,6- tribromophenol [2,4,6-TBP]) can be found in so many sources commonly used in wineries. [....] 2,4,6-TBP and its derivatives have been used as 1) fire-retardant agents in epoxy resins, polyurethanes, plastics, paper, textiles, and fire extinguishing media; 2) wood preservatives; 3) general fungicides for the leather, textiles, paint, plastics, paper, and pulp industries; and 4) antiseptic agents. 5) They have also been found in detergents containing bromine.
 
“The winery environment has several possible sources of 2,4,6-TBP, such as painted surfaces in the cellar, sealants, barrels, oak adjuncts, wood ladders, wooden catwalks, wood pallets, plywood, wooden rafters, wood beams, water, water hoses, wine hoses, plastic tank liners, plastics, insulation, filter pads, fining agents, packaging materials (cardboard, adhesives, paper bags), cleansers, and sanitizers.”
My research yields the potential for silicon bungs to also transmit TBA directly to wine. Admin
 
From another report issued in 2006 from the Mosel Research Institute, concerning the possible sources of TBA contamination,
 
Synthetic closures
filter layers [sic]
wood pallets
cardboard boxes
plastic repackaging materials
plastic seals of crown corks (basic wines for sparkling wine
plastic seals of screw caps
 
The paper describes 3 documented cases of TBA taint having nothing to do with cork stoppers. One concerns a ship transporting plastic stopper from the US to Europe. Taint was readily evident upon reaching its destination. The cause was the presence of TBP-contaminated wooden flooring and paints which, under the poorly ventilated conditions and in the presence of high humidity in the ship’s hold, encouraged microbial growth and, therefore, the production of TBA. Another detailed account involved fungicide-treated cardboard, a vector, left near the bottling line. A third case involved TBA contamination of filter layers and plastic foils within a winery.
 
It is critically important to note the wide spread use of TBA’s precursor, TBP, in ordinary, everyday chemical compounds; paints, fire retardants, fungicides, pesticides (even some approved by Integrated Pest Management), et al. So, how common is the taint in wines? Unfortunately, we cannot say. TCA research and bad publicity (not to mention the infamous R. Grahm Funeral for cork some years ago), seems to have, in the short term at least, blunted a wider popularization of either the rate or even existence of TBA contamination. Indeed, in 2 emails from Dr. Ron Jackson he put it this way:
 
“What makes me ponder, though, is the absence of data on the actual prevalence of 2,4,6-TBA, at sensory detectable levels, in wine. It is six years since Chatonnet’s article. Is that an indicator of comparative insignificance, or simple lack of investigation? Without someone to study and report on its frequence I have no way of even guessing at its overall importance.”
 
It is also true that assorted companies offer TBP and TBA testing of the winery environment, ETS Laboratories, for example. And Mavrik offers removal services for both TCA and TBA. Indeed, an email to Mavrik President, Dr. Bob Kreisher, he wrote the following,
 
“Removal of both is pretty similar. When somebody has a relatively low level (say threshold to 5 pptr), we advise them to use special filter pads impregnated w/ a polymer. This strips the anisoles, as well as some phenols. I believe Heyes Filters sells one, and maybe Gusmer. This solution costs maybe $.05 to $.10 per gallon.
 
“If the level is very high, you may end up stripping the wine (in my subjective opinion). In that case, we have a process where we separate the wine into a phenol-free stream and a phenol-rich stream. We treat only the phenol-free stream to a proprietary adsorbent. This gives you a very clean and low-impact removal. It can run from about $.25 per gallon and up depending on level and volume of wine.
 
“There are also others who offer a service of running the wine through a bed of polymer beads. This is essentially the same as the filter pad solution mentioned above. The main difference is it costs several times more.”

 
So, just how prevalent is the problem is unclear. A recent 2009 article in the Wine Spectator restates the broad outlines of my complaint of the naming of but a single tainting agent.
 
“Corks are made from the bark of cork trees, and various fungi live inside the fine pores that give cork its light, springy structure. Certain conditions cause the fungi to produce various chemical compounds that can affect a wine’s flavor. The most notable is 2,4,6-trichloroanisole (TCA). These compounds give the wine that musty, moldy flavor and aromas.
 
“The cork industry has spent decades trying to eliminate TCA and its friends. When chlorine- and bromine-based pesticides sprayed on cork trees and chlorine bleaches used to wash cork planks were suspected of triggering the fungi, they were eliminated, but taint kept popping up. Now Amorim and other producers use various cleaning processes. Some test the corks with gas chromatography-mass spectrometry to detect TCA early on and reject the cork. While the industry says the methods have reduced the number of bad corks, others remain skeptical.”

 
TCA’s friends? Most notable is the author’s remark concerning the elimination of chlorine bleaching and the use of chlorine and bromine-based pesticides in cork oak forests, “but taint kept popping up”. Of course it did because the precursor TBP has multiple environmental sources unrelated to either cork oak stewardship or cork manufacture! I find it quite incredible, in light of the new scientific research on the matter of bromine-based taint, TBA, that such a thing might still be said.
 
Inasmuch as wine may be directly contaminated by 2,4,6-tribromoanisole, because of the high degree of probability of the precursor TBP already being present through multiple equipment and structural vectors in a winery environment, and because of the absence of historically documented research and identification of the occurrence of TBA, it becomes impossible to state whether anecdotally reported ‘cork taint’ is a result of a TCA-infected cork stopper and not TBA etc.
 
In the Oxford Companion to Wine, 3rd ed., we may the following under the subject heading of cork taint, “[D]espite a few fairly high-profile instances of winery contamination [by TBA], it seems that the cork is the culprit in the vast majority of cases”. How is such a sentence authorized given that the first formal, scientific description of TBA and its generation and vectors was only published by Chatonnet et al. in 2004? Are we to realistically believe that after cork stoppers have been widely publicized for years as the only likely source of taint, that anyone would or even could claim otherwise? I mean, when an expert writes in a popular publication that a wine was corked, what are the chances it was scientifically tested for the presence or absence of TCA? Very near zero would be my guess.
 
Hence my modest plea. A wine may be said to be HAloanisole Contaminated, or ‘hacked’, and no longer exclusively corked. Cheers.
 
For further reading, see Causes and Origins of Wine Contamination By Haloanisoles, Institute of Biotechnology of León, Spain (INBIOTEC)
 
Admin

 

18 Responses to ' HAC(k)ing a Wine, The New Science Of Cork Taint '

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  1. on December 5th, 2010 at 11:51 pm

    Ken, thank you for this insightful and well-researched article. I remember visiting the cork forest and the Amorim cork facilities with you in Portugal and wanting to know more about why cork had developed such a bad reputation. I think you’ve got a great idea here and I will do what I can to contribute to its adoption.

  2. Admin, Ken Payton said,

    on December 5th, 2010 at 11:56 pm

    Thank you, Gwendolyn. I think it is long past due that the concept of ‘cork taint’ be retired. Any help you might provide would surely be appreciated.

  3. Rich said,

    on December 6th, 2010 at 11:48 am

    Why does the cork industry still spend so much money having the corks tested and subsequently grade the corks according to the extractable TCA levels. I have been through the indoctrination the cork suppliers would like the wine industry to believe. If your supplier tells you the binder in your agglomerated, twin disk or granulated is causing the musty smell on your cork they are perpetuating the a lie. If you smell TCA my experience has been proven it is TCA or one of its friends. The cork industry is betting the extractable TCA will be below the sensory threshold i.e. less than 2.0 ng/L and will not taint the wine. I have been down this path. If suspect TCA…do not buy the standard BS that the binder is causing the musty smell.

  4. Admin, Ken Payton said,

    on December 6th, 2010 at 11:54 am

    Thank you for the comment, Rich. I am not in a position to answer your question as it is outside the scope of my presentation. I do hope a cork industry rep. might read your remarks and offer a comment. Cheers.


  5. on December 6th, 2010 at 1:36 pm

    Ken,
    Fantastic article, and your terminology recommendation is duly noted. I’ll be sure to pass this on, and help to disconnect the cork itself from the nasty adjective it has become.

    For what it is worth, we’ve been extremely lucky at home in the last couple of years, only recently did we pull a bottle that was [HAC'd]…putting us at a fraction of 1% as compared to the higher ratios often publicised.
    Cheers!
    Todd

  6. Admin, Ken Payton said,

    on December 6th, 2010 at 2:14 pm

    Wonderful comment, Todd. I think HAC’d has potential!

  7. 1WineDude said,

    on December 7th, 2010 at 9:28 am

    I think the cork industry ought to offer you guys some cash to research this further! :)

    Great stuff.

  8. Admin, Ken Payton said,

    on December 7th, 2010 at 10:03 am

    Thanks for stopping by, Joe. I am pleased your comment came through. Been having trouble with my email service. Some comments have been bounced back. I hope those folks try again! Cheers.

  9. Admin, Ken Payton said,

    on December 7th, 2010 at 11:16 am

    Folks, I am having difficulty receiving some comments. My email service provider is working on the issue. Please note that I post all comments received. That a visitor’s remarks might not appear is entirely the function of an over-zealous spam blocker. Apologies.


  10. on December 7th, 2010 at 11:24 am

    Now in the Finger Lakes we have another thing to worry about: some of the chemicals used in that nasty practice of hydrofracking to extract natural gas would probably contaminate vineyard posts, trees, etc. and surely get into the wine.

    Instead of HACked we might have to call the wines frHACked!

    Informative article, Ken.

  11. Admin, Ken Payton said,

    on December 7th, 2010 at 11:28 am

    Thank you, Thomas. ‘frHACed’ is a brilliant idea!

  12. Ted Henry said,

    on December 7th, 2010 at 3:01 pm

    There seems to be a question of if the cork can be blamed for a tainted bottle of wine. Can’t this be solved by opening another bottle. If not tainted it must be the stopper right?

    I have no doubt that entire wineries (or barrels etc.)can be HAC’d but there would be little bottle to bottle variation.

    Anyway, a good topic and a cool term you coined. I think I will start using it immediately.

  13. Admin, Ken Payton said,

    on December 7th, 2010 at 3:59 pm

     
    Thank you, for your comment, Ted. As I read the research, it must be remembered that a cork is not just a carrier from TCA-contaminated cork slabs, but that it also readily absorbs compounds from the environment, 2,4,6TBA included. And so do plastic stoppers and the liners of screw caps. Now, whatever closure is used, a winery environment contaminated with TBA (wooden beams, floors, fire retardant paints etc.) or from TBA-contaminated materials brought into an otherwise clean winery (barrels, cardboard boxes, pallets, plastics etc.), the contamination of closures need not be uniform. It depends on how and where they are stored, whether in bags or boxes, and how close to the offending source. Since a bag of cork stoppers has some in the center of the bag, those are less likely to be tainted from an enviro source. Those nearer the outside of the bag, or exposed to the air, will have a high likelihood of TBA contamination. Therefore, you would have an uneven distribution of TBA taint. Some corks, but not others. Some stoppers, but not others. Remember that TBA taint will effect ANY stopper.
     
    A complicating factor is that through contaminated bungs, hoses and barrels, an entire barrel of wine might be tainted. Were the wine then be sealed under cork, the taint later detected would naturally be blamed on the cork. And this is what may in fact happen. Ironically, because of cork’s absorptive character, should it be used to seal an already TBA-tainted wine, it will actually soak up quantities of the compound! Indeed, a cork might just remove sufficient quantities of taint so as to make the wine less offensive, or perfectly acceptable!
     
    So, knowing the uneven distribution of TBA taint within a winery, that it depends on the proximity of a wine and/or stoppers to the TBA source(s); knowing the mixed nature of a bag of stoppers, some deep, some near the surface or a bag or box (itself possibly contaminated); and knowing that a tainted barrel of wine may be only one of a number of barrels bottled on a given day, then, no: Choosing another bottle of the same wine after the first was tainted and finding it ‘clean’, would not necessarily mean the cork by itself was at fault, certainly not without a scientific analysis of the cork, the wine, and, especially the winery.
     
    Two last observations. It is reported that expert tasters cannot tell the difference between TCA and TBA contaminated wine. And, the much ballyhooed tasting threshold of 2-6 ppt for TCA (higher for TBA), is quite rare in real life. According to Dr. Ron Jackson, many people cannot detect taint even at 200 ppt and beyond!
    Oh, and using the term HAC(k)ed, cool! I think it more accurately describes what is going on.
     
    Cheers.


  14. on December 7th, 2010 at 8:25 pm

    excellent…I smell some inertia with the new terminology.

  15. Admin, Ken Payton said,

    on December 7th, 2010 at 8:31 pm

    As do I, Todd. It would be good for the cork and screw cap industries, not to mentions wineries. Frank analysis is the best cleanser. And a new, more precise terminology surely helps the science along. Cheers.

  16. Butler said,

    on December 17th, 2010 at 5:16 am

    Thanks for this very informative article. I assume such data would have been included in this very thorough article if available but am curious whether there is any information re: whether poly vs cork are more likely to absorb/desorb these compounds?

    Perhaps it doesn’t matter since it takes so little.

    But one reason I ask, is that in my understanding – based on a Biologist friend’s undergrad lab experiment wherein he found that plastic cutting boards harbor more bacteria than wood cutting boards due to what he then described as wood retaining an “immune system” long after becoming a cutting board) – plastic could perhaps actually be more prone to harboring the microbes responsible for this sort of contamination, than wood?

    I don’t know details or the repeatability of the above-mentioned experiment or whether cork would have the same sort of anti-bacterial properties as a hardwood board apparently does, but thought this might be of interest in this context.

    I’ve always hated plastic cutting boards anyway…

  17. Admin, Ken Payton said,

    on December 17th, 2010 at 6:09 am

    Thank you for the comment, Butler. A couple of things: With respect to stoppers, whether plastic, screw cap, or cork, the detail to keep in mind is that it is ultimately the stopper surface in contact with the wine that is of moment. Analysis of TCA in the interior of a cork stopper, for example, shows zero migration into wine. So assuming the presence of TBA in a winery environment (or any haloanisole), it would only matter with respect to HAC were the compound to settle upon the ends of a stopper, assuming a tight fit, of course. I do not have info on whether migration can occur with plastic stoppers, but we can perhaps assume, given the smaller drinking window of such wines, that the end surfaces would, nevertheless, be of greater consequence.
     
    And you are right about how little of an offending compound it takes. We’re talking nanograms here. But far more important is the potential for contamination of the wine itself before bottling. The more salient feature of my piece and the research cited is TBA generated by a fungal defense mechanism to the presence of precursors in common winery materials: Cardboard, pallets, paints, barrels, silicon bungs etc. HAC may also occur in tasting glasses and bottles stored in contaminated boxes as well. The point is that HAC can come from stoppers AND wine. And because of cork’s absorptive character (perhaps plastic stoppers as well, though I’ve read nothing in this regard) HAC compounds may actually be removed from a HACed wine. The upshot in this scenario would be that far from a cork stopper being the cause of HAC, it might be part of the remedy, removing sufficient nanograms of a HAC compound so as to render the wine drinkable! OR being blamed for HAC which has actually originated in the wine stored in a compromised winery.
     
    Your cutting board example is very interesting with respect to the greater absolute potential of either wood or plastic cutting boards to absorb or harbor microbes. But inasmuch as we are talking about fungal interaction with precursors, I am not sure whether bacterial contamination of either materials’ surface matters to wine. It might. Molds must also be present. People get sick from cutting boards all the time, but also sponges etc. It is a question of wine contact with haloanisoles by contaminated vectors. Cheers.


  18. on March 7th, 2011 at 8:38 pm

    [...] and iodine may be implicated also. Read a thorough review of the subject in this great blog article. Tweet Filed in [...]

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