Wine fault due to aroma-intense compounds present in the cork
Chemical structure of 2,4,6-trichloroanisole (TCA), the compound primarily responsible for cork taint
Cork taint is a broad term referring to an off-odor and off-flavor wine fault[1] arising from the presence in the cork of aroma-intense compounds that are transferred into wine after bottling.[2]
Cork taint is characterized by a set of undesirable smells or tastes found in a bottle of wine, described as "musty", "mouldy", "earthy",[2] or "mushroom".[3] It causes losses to the industry (the estimated share of affected bottles is between 1% and 5%), and can destroy the reputation of a winery that is particularly unlucky (in rare cases up to a third of the bottles can be tainted).[4] A wine found to be tainted on opening is said to be corked or "corky".
Not every contaminant in the cork is considered a "cork taint": for the issue to be classified as such, the problem should be caused by a compound introduced due to normal cork processing or forming in the cork naturally (for example, external naphthalene contamination during transportation is excluded). There are multiple sources of cork taint, but the 2,4,6-trichloroanisole (TCA) is by far most prevalent, with estimated 80-85% of all cork taints due to TCA. Occasionally, the same compounds found in the wine are not there due to the cork, but actually are introduced before bottling from the grapes, wooden barrels, and processing equipment.[2]
The role of TCA in tainting the foodstuffs is known since at least 1970s. In 1982, Buser et al. identified TCA as a compound causing the cork taint.[5] TCA is studied in detail[6] and considered to be the main source of the issue (in some surveys, the TCA was present in all the bottles assessed to be tainted).[7] Humans are very sensitive to the presence of TCA, with some experts capable of detecting the levels as low as 1-2 ng/liter, and a specially trained group reported to achieve a threshold of 0.3 ng/L. Individual sensitivity greatly varies, with some experts' threshold at 250 ng/L, while some assessors unfamiliar with the TCA odors were able to detect the problem only at mg/L levels.[8]
In side-by-side comparisons for white wines, one panel had shown preference for non-corked wines at the level of 20 ng/L of TCA, while another study found the "rejection threshold" to be between 3.1 and 3.7 ng/L.[7]
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The cork-industry group APCOR cites a study showing a 0.7–1.2% taint rate. In a 2005 study of 2800 bottles tasted at the Wine Spectator blind-tasting facilities in Napa, California, 7% of the bottles were found to be tainted.[11]
In 2013, the Cork Quality Council ran over 25 thousand tests. The results, compared with data from eight years before, showed a sharp reduction in TCA levels, of around 81 percent. In the last test, 90 percent of samples of natural cork stopper shipments showed values of under 1.0 ppt and only 7 percent showed results of 1.0–2.0 ppt.[12]
Improvements in cork and winemaking methodology continue to strive to lower the incidence, but the media attention given to cork taint has created a controversy in the winemaking community, with traditional cork growers on one side and the makers of newer synthetic closures and screw caps on the other. Screw caps and synthetic corks, however, are thought to be prone to another aroma taint: sulphidisation. This may arise from the reduced oxygen supply which concentrates sulphurous smells arising from wines with universal preservatives, however it is more likely that these wines contain excessive/imbalanced amounts of sulphite based preservatives to begin with.[13]
Systemic TCA tainting occurs when TCA has infiltrated a winery via means other than cork and can affect the entire production of wine instead of just a few bottles.[14][bettersourceneeded] This occurs when wine barrels, drain pipes, wooden beams in the cellars, or rubber hoses are tainted by TCA.[14][bettersourceneeded] Sometimes entire cellars have to be rebuilt in order to eliminate all potential systemic TCA culprits.[14][bettersourceneeded][verification needed]
Rubber hoses or gaskets have a high affinity for TCA and therefore concentrate TCA from the atmosphere; wine or water that subsequently passes through infected hoses can become tainted with TCA.[citation needed] Another possible means of TCA contamination is through the use of bentonite, a swelling clay preparation (smectite) used in treating wine for heat stability; bentonite has a high affinity for TCA and will absorb TCA and related chemicals in the atmosphere, so if an open bag of bentonite is stored in an environment with a high (1–2ng/g or ppb) TCA concentration, TCA will be absorbed in the bentonite and transferred to the wine lot to which the bentonite is added.[citation needed]
It is notable that this systemic TCA will often impart a trace (1–2ng/L or ppt) to the wine, which itself is not detected by most consumers.[according to whom?][citation needed] However, with this high baseline level of TCA in bottled wine, even the additional contribution of a relatively clean cork can elevate the TCA level in the wine above threshold levels (4–6ng/L or ppt), rendering the wine "corked".[citation needed]
Filtration and purification systems now exist that attempt to remove the TCA from corked wine to make it drinkable again, though there are few means of reducing the level of TCA in tainted wine that are approved by the TTB (formerly BATF).[citation needed]
One method of removing TCA from tainted wine is to soak polyethylene (a plastic used for applications such as milk containers and plastic food wrap) in the affected wine; the non-polar TCA molecule has a high affinity for the polyethylene molecule, thereby removing the taint from the wine.[citation needed] The surface area of polyethylene needed to reduce the taint to sub-threshold levels is based on the TCA level in the affected wine, temperature, and the alcohol level of the wine.[citation needed]
Some vintners have used the so-called half and half mix of milk and cream to remove TCA from wine (the TCA in the wine is sequestered by the butterfat in half and half).[citation needed] The French company Embag markets a product called "Dream Taste", which uses a copolymer shaped like a cluster of grapes that is designed to remove the TCA taint from wine.[citation needed]
As advocated by Andrew Waterhouse, professor of wine chemistry at University of California, Davis, this can be done at home by pouring the wine into a bowl with a sheet of polyethylene plastic wrap; for ease of pouring, a pitcher, measuring cup, or decanter can be used instead, and the 2,4,6-trichloroanisole will stick to the plastic in a process effective within a few minutes.[15]
↑ A wine fault is a sensory-associated (organoleptic) characteristic of a wine that is unpleasant, and may include elements of taste, smell, or appearance, elements that arise from a "chemical or a microbial origin", where particular sensory experiences (e.g., an off-odor) might arise from more than one wine fault. See Watrelot, Aude; Savits, Jennie & Moroney, Maureen (2020). "Wine Fault Series"(PDF). ISU Extension and Outreach (Extension.IAState.edu). Ames, IA: Iowa State University (ISU). Retrieved June 26, 2023.{{cite web}}: CS1 maint: multiple names: authors list (link) See also Merriam-Webster. (n.d.). Organoleptic. In Merriam-Webster.com dictionary. Retrieved June 26, 2023, from https://www.merriam-webster.com/dictionary/organoleptic.
Tindale CR, Whitefield FB, Levingston SD, Nguyen THL (1989). "Fungi Isolated from Packing Materials - Their Role in the Production of 2,4,6-Trichloroanisole". Journal of the Science of Food and Agriculture. 49 (4): 437–447. Bibcode:1989JSFA...49..437T. doi:10.1002/jsfa.2740490406.
Pirbazari M, Borow HS, Craig S, Ravindran V, McGuire MJ (1992). "Physical-Chemical Characterization of 5 Earth-Musty-Smelling Compounds". Water Science and Technology. 25 (2): 81–88. doi:10.2166/wst.1992.0038.
Marsili, R. (2000). "Solid-Phase Microextraction: Food Technology Applications". In Wilson, Ian D. (ed.). Encyclopedia of Separation Science. New York, NY: Academic Press. pp.4178–4190. doi:10.1016/B0-12-226770-2/06791-0. ISBN9780122267703. Over the last two decades, the incidence of mouldy and musty off-flavours in cork-sealed wines has increased significantly. 2,4,6-Trichloroanisole (TCA) has been identified as the primary chemical responsible for cork taint. The human olfactometry threshold for TCA is 4–10 ng L−1 in white wine and 50 ng L−1 in red wine. In the case of wine, a worldwide loss of roughly US$1 billion per year is attributed to cork taint.
Science Direct Staff (June 2023). "2-4-6-Trichloroanisole"(Science Direct citation sample/listing). Retrieved June 26, 2023.
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