Cork taint

The primary chemical precursor to TCA is TCP (2,4,6-trichlorophenol), a solvent used for industrial cleaning.^{[citation needed][3]} Bacteria is able to de-toxify TCP, notably Pseudomonas and Stenotrophomonas, but both strains cannot de-toxify the TCP without the other. ^{[better source needed][4]} Chlorinated phenols can form chemically when hypochlorous acid (HOCl, one of the active forms of chlorine) or chlorine radicals come in contact with wood (untreated, such as barrels or pallets).^{[citation needed]} The use of chlorine or other halogen-based sanitizing agents is being phased out of the wine industry in favor of peroxide or peracetic acid preparations.^{[citation needed]} Chlorine dioxide has not been shown to produce these spontaneous chlorophenols.^{[citation needed]} Chlorine dioxide is a relatively new agent being used in the wine industry due to its obvious advantages, having shown no evidence of the possibility of TCA formation.^{[citation needed]}

The production of TCA in cork or its transfer by other means into wine is complex, but most results when naturally occurring airborne fungi are presented with chlorophenol compounds, which they then convert into chlorinated anisole derivatives. Chlorophenols taken up by cork trees are an industrial pollutant found in many pesticides and wood preservatives, which may mean that the incidence of cork taint has risen in modern times. Chlorophenols can also be a product of the chlorine bleaching process used to sterilize corks (not in use anymore); this has led to the increasing adoption of methods such as peroxide bleaching.

TCA and TBA are responsible for the vast majority of cases of cork taint, but other less common and less known compounds that can cause different varieties of cork taint include guaiacol, geosmin, 2-methylisoborneol (MIB), octen-3-ol and also octen-3-one, each with its own particular aroma, but all considered objectionable in wine.

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.^[5]

In 2013, the Cork Quality Council ran over 25 thousand tests. The results, compared with data from eight years ago, show 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 had showed results of 1.0–2.0 ppt.^[6]

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.^[7]

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.^{[8][better source needed]} This occurs when wine barrels, drain pipes, wooden beams in the cellars, or rubber hoses are tainted by TCA.^{[8][better source needed]} Sometimes entire cellars have to be rebuilt in order to eliminate all potential systemic TCA culprits.^{[8][better source needed][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 (1–2 ng/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 (1–2 ng/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 (4–6 ng/L or ppt), rendering the wine "corked".^{[citation needed]}

Wine Spectator has reported that such California wineries as Pillar Rock Vineyard, Beaulieu Vineyard, and E & J Gallo Winery have had trouble with systemic TCA.^{[8][verification 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.^[9]

• Alternative wine closure
• Flavor scalping
• Wine fault

• Buser HR, Zanier C, Tanner H (1982). "Identification of 2,4,6-Trichloroanisole as a Potent Compound Causing Cork Taint in Wine". Journal of Agricultural and Food Chemistry. 30 (2): 359–382. doi:10.1021/jf00110a037.
• 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. 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 Yor, NY: Academic Press. pp. 4178–4190. doi:10.1016/B0-12-226770-2/06791-0. ISBN 9780122267703. 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.

• Nase, Joseph. "The sommelier. Bad Wine: The four most common defects and how to detect them". New York Magazine. Retrieved 8 March 2021.