Cork taint
Encyclopedia
Cork taint is a broad term referring to a wine fault
characterized by a set of undesirable smells or tastes found in a bottle of wine
, especially spoilage that can only be detected after bottling, aging
and opening. Though modern studies have shown that other factors can also be responsible for taint – including wooden barrels, storage conditions and the transport of corks and wine – the cork
stopper is normally considered to be responsible, and a wine found to be tainted on opening is said to be "corked" or "corky". Cork taint can affect wines irrespective of price and quality level.
The chief cause of cork taint is the presence of 2,4,6-trichloroanisole
(TCA), and/or 2,4,6-tribromoanisole
(TBA), in the wine, which in many cases will have been transferred from the cork, but which also can have been transferred through the cork rather than from it. Corked wine containing TCA has a characteristic odor, variously described as resembling a moldy newspaper, wet dog, damp cloth, or damp basement. In almost all cases of corked wine the wine's native aromas
are reduced significantly, and a very tainted wine is quite unpalatable, although harmless. While the human threshold for detecting TCA is measured in the single-digit parts per trillion, this can vary by several orders of magnitude depending on an individual's sensitivity. Detection is also complicated by the olfactory system
's particularly quick habituation
to TCA, making the smell less obvious on each subsequent sniff.
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 pesticide
s and wood preservative
s, which may mean that the incidence of cork taint has risen in modern times. Ironically, chlorophenols can also be a product of the chlorine
bleaching process used to sterilize
corks; 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 include guaiacol
, geosmin
, 2-methylisoborneol
(MIB), octen-3-ol
and octen-3-one
- each has its own aroma, all of them considered objectionable in wine.
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.
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 winemaking, 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, can be prone to another aroma taint: sulphidisation, which arises from the reduced oxygen supply which concentrates sulphurous smells arising from universal preservatives.
, a clay preparation used in treating wine for heat stability. Bentonite has a high affinity for TCA and will absorb TCA and related chemicals in the atmosphere. If an open bag of Bentonite is stored in an environment with a high (1-2 ng/g or ppb) TCA concentration, this TCA will be absorbed in the Bentonite and transferred to the wine lot to which the Bentonite is added.
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. 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."
The primary chemical precursor to TCA is TCP (2,4,6-Trichlorophenol
), an anti-microbial agent used in processing wood. Molds (and some suspect bacteria such as Streptomyces
) are able to de-toxify TCP by methylating the -OH to -OCH3, which is not toxic. 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 barrel
s or pallet
s.) 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. Chlorine dioxide
has not been shown to produce these spontaneous chlorophenols. Wine Spectator has reported that such California wine
ries as Pillar Rock Vineyard, Beaulieu Vineyard
, E & J Gallo Winery
and Chateau Montelena
have had trouble with Systemic TCA.
(formerly BATF
).
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. 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.
This can be done at home, as advocated by Andrew Waterhouse, professor of wine chemistry
at University of California, Davis, 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. Effective within a few minutes, the 2,4,6-trichloroanisole molecule is chemically similar to polyethylene and will stick to the plastic.
Some vintners have used Half & Half to remove TCA from wine (the TCA in the wine is sequestered by the butterfat in Half & Half).
The French company Embag markets a product called "Dream Taste" which uses a copolymer shaped like a cluster of grapes to remove the TCA taint from wine.
Wine fault
A wine fault or defect is an unpleasant characteristic of a wine often resulting from poor winemaking practices or storage conditions, and leading to wine spoilage. Many of the compounds that cause wine faults are already naturally present in wine but at insufficient concentrations to adversely...
characterized by a set of undesirable smells or tastes found in a bottle of wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...
, especially spoilage that can only be detected after bottling, aging
Aging of wine
The aging of wine, and its ability to potentially improve wine quality, distinguishes wine from most other consumable goods. While wine is perishable and capable of deteriorating, complex chemical reactions involving a wine's sugars, acids and phenolic compounds can alter the aroma, color,...
and opening. Though modern studies have shown that other factors can also be responsible for taint – including wooden barrels, storage conditions and the transport of corks and wine – the cork
Cork (material)
Cork is an impermeable, buoyant material, a prime-subset of bark tissue that is harvested for commercial use primarily from Quercus suber , which is endemic to southwest Europe and northwest Africa...
stopper is normally considered to be responsible, and a wine found to be tainted on opening is said to be "corked" or "corky". Cork taint can affect wines irrespective of price and quality level.
The chief cause of cork taint is the presence of 2,4,6-trichloroanisole
2,4,6-Trichloroanisole
2,4,6-Trichloroanisole is a chemical compound that is a chlorinated derivative of anisole.Trichloroanisole is a fungal metabolite of 2,4,6-trichlorophenol, which is used as a fungicide. It can be found in minute traces on packaging materials stored in the presence of fiberboard treated with...
(TCA), and/or 2,4,6-tribromoanisole
2,4,6-Tribromoanisole
2,4,6-Tribromoanisole is a chemical compound that is a brominated derivative of anisole. It is one of the chemicals responsible for cork taint....
(TBA), in the wine, which in many cases will have been transferred from the cork, but which also can have been transferred through the cork rather than from it. Corked wine containing TCA has a characteristic odor, variously described as resembling a moldy newspaper, wet dog, damp cloth, or damp basement. In almost all cases of corked wine the wine's native aromas
Aroma of wine
It is through the aromas of wine that wine is actually tasted. The human tongue is limited to the primary tastes perceived by taste receptors on the tongue-acidity, bitterness, saltiness, sweetness and umami. The wide array of fruit, earthy, floral, herbal, mineral and woodsy flavor perceived in...
are reduced significantly, and a very tainted wine is quite unpalatable, although harmless. While the human threshold for detecting TCA is measured in the single-digit parts per trillion, this can vary by several orders of magnitude depending on an individual's sensitivity. Detection is also complicated by the olfactory system
Olfactory system
The olfactory system is the sensory system used for olfaction, or the sense of smell. Most mammals and reptiles have two distinct parts to their olfactory system: a main olfactory system and an accessory olfactory system. The main olfactory system detects volatile, airborne substances, while the...
's particularly quick habituation
Habituation
Habituation can be defined as a process or as a procedure. As a process it is defined as a decrease in an elicited behavior resulting from the repeated presentation of an eliciting stimulus...
to TCA, making the smell less obvious on each subsequent sniff.
Production
The production of TCA in cork or its transfer by other means into wine is complex, but most results when naturally-occurring airborne fungiFungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
are presented with chlorophenol
Chlorophenol
A chlorophenol is any organochloride of phenol that contains one or more covalently bonded chlorine atoms. Chlorophenols are produced by electrophilic halogenation of phenol with chlorine. Most chlorophenols have a number of different isomers...
compounds, which they then convert into chlorinated anisole
Anisole
Anisole, or methoxybenzene, is the organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances...
derivatives. Chlorophenols taken up by cork trees are an industrial pollutant found in many pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s and wood preservative
Preservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
s, which may mean that the incidence of cork taint has risen in modern times. Ironically, chlorophenols can also be a product of the chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
bleaching process used to sterilize
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...
corks; this has led to the increasing adoption of methods such as peroxide
Peroxide
A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion .The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.The simplest stable peroxide is hydrogen 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 include guaiacol
Guaiacol
Guaiacol is a naturally occurring organic compound with the formula C6H4. Although it is biosynthesized by a variety of organisms, this colorless aromatic oil is usually derived from guaiacum or wood creosote. Samples darken upon exposure to air and light. Guaiacol is present in wood smoke,...
, geosmin
Geosmin
Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather or when soil is...
, 2-methylisoborneol
2-Methylisoborneol
2-Methylisoborneol is an organic chemical with a strong odor. It is a derivate of borneol. Its odor detection threshold is very low and it is one of the chemicals with major influence on the quality of drinking water...
(MIB), octen-3-ol
1-Octen-3-ol
1-Octen-3-ol, octenol for short , is a chemical that attracts biting insects such as mosquitos. It is contained in human breath and sweat, and it was once believed that insect repellent DEET works by blocking the insects' octenol odorant receptors.Octenol is used in combination with carbon dioxide...
and octen-3-one
Oct-1-en-3-one
Oct-1-en-3-one , also known as 1-octen-3-one, is the odorant that is responsible for the typical metallic smell of metals and blood coming into contact with skin...
- each has its own aroma, all of them considered objectionable in wine.
Estimated occurrence of cork taint and industry response
The cork-industry group APCORAPCOR
Associação Portuguesa da Cortiça is the Portuguese Cork Association, a consortium of cork growers and manufacturers. It was founded in 1956 and is based in the town of Santa Maria de Lamas in northern Portugal...
cites a study showing a 0.7-1.2% taint rate. In a 2005 study of 2800 bottles tasted at the Wine Spectator
Wine Spectator
Wine Spectator is a lifestyle magazine that focuses on wine and wine culture. It publishes 15 issues per year with content that includes news, articles, profiles, and general entertainment pieces...
blind-tasting facilities in Napa, California, 7% of the bottles were found to be tainted.
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
Controversy
Controversy is a state of prolonged public dispute or debate, usually concerning a matter of opinion. The word was coined from the Latin controversia, as a composite of controversus – "turned in an opposite direction," from contra – "against" – and vertere – to turn, or versus , hence, "to turn...
in winemaking, with traditional cork growers on one side and the makers of newer synthetic closures
Alternative wine closures
Alternative wine closures are substitute closures used in the wine industry for sealing wine bottles in place of traditional cork closures. The emergence of these alternatives has grown in response to quality control efforts by winemakers to protect against "cork taint" caused by the presence of...
and screw caps on the other. Screw caps and synthetic corks, however, can be prone to another aroma taint: sulphidisation, which arises from the reduced oxygen supply which concentrates sulphurous smells arising from universal preservatives.
Systemic TCA
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. This occurs when wine barrels, drain pipes, wooden beams in the cellars, or rubber hoses are tainted by TCA. Sometimes entire cellars have to be rebuilt in order to extinguish all potential systemic TCA culprits. 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. Another possible means of TCA contamination is through the use of BentoniteBentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
, a clay preparation used in treating wine for heat stability. Bentonite has a high affinity for TCA and will absorb TCA and related chemicals in the atmosphere. If an open bag of Bentonite is stored in an environment with a high (1-2 ng/g or ppb) TCA concentration, this TCA will be absorbed in the Bentonite and transferred to the wine lot to which the Bentonite is added.
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. 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."
The primary chemical precursor to TCA is TCP (2,4,6-Trichlorophenol
2,4,6-Trichlorophenol
2,4,6-Trichlorophenol, also known as TCP, phenaclor, Dowicide 2S, Dowcide 2S, omal, is a chlorinated phenol that has been used as a fungicide, herbicide, insecticide, antiseptic, defoliant, and glue preservative. It is a yellow solid with a strong, sweet odour...
), an anti-microbial agent used in processing wood. Molds (and some suspect bacteria such as Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
) are able to de-toxify TCP by methylating the -OH to -OCH3, which is not toxic. Chlorinated phenols can form chemically when hypochlorous acid (HOCl-, one of the active forms of chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
) or chlorine radicals come in contact with wood (untreated, such as barrel
Barrel
A barrel or cask is a hollow cylindrical container, traditionally made of vertical wooden staves and bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. A small barrel is called a keg.For example, a...
s or pallet
Pallet
A pallet , sometimes called a skid, is a flat transport structure that supports goods in a stable fashion while being lifted by a forklift, pallet jack, front loader or other jacking device. A pallet is the structural foundation of a unit load which allows handling and storage efficiencies...
s.) The use of chlorine or other halogen-based sanitizing agents is being phased out of the wine industry in favor of peroxide
Peroxide
A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion .The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.The simplest stable peroxide is hydrogen peroxide...
or peracetic acid preparations. Chlorine dioxide
Chlorine dioxide
Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching....
has not been shown to produce these spontaneous chlorophenols. Wine Spectator has reported that such California wine
California wine
California wine has a long and continuing history, and in the late twentieth century became recognized as producing some of the world's finest wine. While wine is made in all fifty U.S. states, up to 90% of American wine is produced in the state...
ries as Pillar Rock Vineyard, Beaulieu Vineyard
Beaulieu Vineyard
Beaulieu Vineyard is a vineyard near Rutherford, California, belonging to the appellation Rutherford AVA. It was established by Georges de Latour and his wife Fernande in 1900.-History:...
, E & J Gallo Winery
E & J Gallo Winery
E & J Gallo Winery was founded in 1933 by Ernest Gallo and Julio Gallo in Modesto, California. E & J Gallo Winery is the largest exporter of California wines and is a large promoter of wines from Sonoma County.-History:...
and Chateau Montelena
Chateau Montelena
Chateau Montelena is a Napa Valley winery most famous for winning the white wine section of the historic "Judgement of Paris" wine competition. Chateau Montelena's Chardonnay was in competition with nine other wines from France and California under blind tasting...
have had trouble with Systemic TCA.
Treatment
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 TTBAlcohol and Tobacco Tax and Trade Bureau
The Alcohol and Tobacco Tax and Trade Bureau, statutorily named the Tax and Trade Bureau and frequently shortened to TTB, is a bureau of the United States Department of the Treasury....
(formerly BATF
Bureau of Alcohol, Tobacco, Firearms and Explosives
The Bureau of Alcohol, Tobacco, Firearms and Explosives is a federal law enforcement organization within the United States Department of Justice...
).
One method of removing TCA from tainted wine is to soak polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
(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. 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.
This can be done at home, as advocated by Andrew Waterhouse, professor of wine chemistry
Wine chemistry
Wine is a complex mixture of chemical compounds in a hydro-alcoholic solution with a pH around 3.- Types of natural molecules present in wine :* Acids in wine* Phenolic compounds in wine* Proteins in wine* Sugars in wine* Tryptophol and amino acids derivatives...
at University of California, Davis, by pouring the wine into a bowl with a sheet of polyethylene plastic wrap
Plastic wrap
Plastic wrap, cling film , cling wrap or food wrap, is a thin plastic film typically used for sealing food items in containers to keep them fresh over a longer period of time...
. For ease of pouring, a pitcher
Pitcher (container)
A pitcher is a container with a spout used for storing and pouring contents which are liquid in form. Generally a pitcher also has a handle, which makes pouring easier.A ewer is a vase-shaped pitcher, often decorated, with a base and a flaring spout...
, measuring cup
Measuring cup
A measuring cup is a kitchen utensil used primarily to measure the volume of liquid or bulk solid cooking ingredients such as flour and sugar, especially for volumes from about 50 mL upwards. The cup will usually have a scale marked in cups and fractions of a cup, and often with fluid measure...
, or decanter
Decanter
A decanter is a vessel that is used to hold the decantation of a liquid which may contain sediment. Decanters are normally used as serving vessels for wine. Decanters vary in shape and design. They are usually made of an inert material and will hold at least one standard bottle of wine...
can be used instead. Effective within a few minutes, the 2,4,6-trichloroanisole molecule is chemically similar to polyethylene and will stick to the plastic.
Some vintners have used Half & Half to remove TCA from wine (the TCA in the wine is sequestered by the butterfat in Half & Half).
The French company Embag markets a product called "Dream Taste" which uses a copolymer shaped like a cluster of grapes to remove the TCA taint from wine.
External links
- "The four most common defects and how to detect them", New York Magazine