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)
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