The literature about musty and moldy taint—the so-called cork taint—in wines is varied because there are many different molecules involved in this wine defect. Chloroanisoles are the most relevant compound responsible for cork taint and of these, 2,4,6-trichloroanisole (TCA) is the most common, but 2,3,4,6-tetrachloroanisole (TeCA) and 2,4,6-tribromoanisole (TBA) can also be responsible of this defect. For other compounds involved in cork taint, geosmin and 2-methylisoborneol (2-MIB) are responsible for earthy off-flavor; pyrazines cause vegetable odors, and guaiacol results in smoked, phenolic and medicinal defects. Off-odors of mushroom in wines are caused by 1-octen-3-ol and 1-octen-3-one coming from grapes contaminated by bunch rot (Botrytis cinerea).
1. Musty and Moldy Taint
Musty and moldy taint in wine is an important off-flavor in the wine production, generally correlated to the cork stoppers used to plug the wine bottles. Cork taint is a pervasive problem in the industry and is known as “gout de bouchon” in French “gusto di tappo” in Italian—literally “taste of cap.” Although commonly called cork taint, it is not always caused by cork stoppers.
Cork stoppers were used for many years in wine industry and they are still very important because many consumers in Europe and China still associate them with high quality wine. After the introduction of competitive caps made of synthetics, screws and glass, manufacturers invested considerable resources to improve the quality of cork caps.
Cork oak (Quercus suber
L.) forest cultivation is an important economic activity in many Mediterranean countries; it is cultivated on about two million hectares—61% in Spain and Portugal, 33% in Morocco, Algeria and Tunisia and 6% in Italy and France 
. Cork oak usage is correlated to the preservation of biodiversity and the reduction of CO2
emissions. The harvest of the cork bark does not necessitate tree cutting because the rhytidome has high insulation capacity; as such, this species produces suckers to recover quickly after a fire and to resist cold and wind 
. Cork oak forest cultivation contributes to the protection of the soil, the creation of the landscape and the regulation of hydrological cycle 
. Cork regenerates after each stripping, and the cork tree can survive the bark loss of more than 50% 
. Moreover, it is a natural, renewable, recyclable and non-toxic resource. Cork oak is used to produce stoppers, but it has many other applications in many different manufacturers industries, included automobile and aeronautical industries 
. Moreover, granulated cork is also the base material for the production of agglomerated corks for beverages.
Specialists can distinguish between “true cork taint” and “moldy off-flavors” 
. Cork taint is very rare; it causes a very unpleasant and putrid odor in wines, and its cause remains unknown. It was speculated that mancha amarela-yellow spot—macchia gialla—can attack Q. suber
L. and modify mechanical, structural and optical properties of cork causing moldy off-flavor in wine. The cellular structures of infected and healthy tissues of cork are different 
, and contaminated cork should not be used in stopper production.
The most common compound responsible for cork taint is 2,4,6-trichloroanisole (TCA), but other compounds like 2,4,6-tribromoanisole (TBA), 2,3,4,6-tetrachloroanisole (TeCA), 1-octen-3-ol, 1-octen-3-one, 2-methylisoborneol, geosmin, pyrazines or guaiacol can be also involved 
. Anisoles, especially TCA, are responsible for at least 80% of the cases of cork taint 
Studies found that moldy-off flavor can be caused by different compounds, and the contamination of the wine is not always attributable to the cork stoppers. It can take place starting from the grapes up to wine storage in the cellar 
. In the OIV (The International Organization of Vine and Wine) document on Sensory Analysis of Wine (http://www.oiv.int/public/medias/3307/review-on-sensory-analysis-of-wine.pdf
), this type of defect is not connected directly to cork.
Cork taint can affect 0.5% and 7% of wines and the estimated cost of cork-related wine spoilage can be over several billions of dollars per year 
. Defects related to the cork cap depreciate the wine and are often the subject of legal disputes between the buyer who suffered the damage and the company that provided them, which often has an insurance policy against this. If the cause is the cork cap generally only a few bottles are affected, while if the cause is another—materials used in the construction of cellars, wooden beams or barrels—the damage can be to the whole production and it can be much more serious.
2.1. 2,4,6-Trichloroanisole (TCA)
TCA is the most pervasive of the haloanisoles compounds affecting cork taint in wine composition. The presence of TCA can depreciate the wine, impairing olfactory or gustative wine characteristics even in quantities lower than the identification threshold. The average consumer may not attribute the depreciation of the product to the cork stopper and therefore attaches it to the wine. TCA is a potent suppressor of olfactory signal transduction at 10–15 mol m−3
TCA concentrations—extremely low for detection 
TCA produces unpleasant odors of mold and wet cardboard to foods and beverages including beer, milk, water, dried fruit, cocoa powder, fish and shellfish. It is the cause “Rio defect” in coffee from Central and South America with odors describes as medicinal, phenolic or iodine-like 
. In brewing beer, TCA causes a typical odor of mold and damp cellar that can contaminate water and other raw materials. TCA can develop on the premises of the brewery or derive from packaging materials 
. Under experimental conditions with artificially contaminated cork stoppers, TCA migration increased with contact surface, temperature and time 
. However, characteristics common to all naturally polluted cork stoppers were not identified. The characteristics of each cork stopper influenced the TCA concentrations.
TCA and other chloroanisoles are attributed to many types of mold that produce moldy-off-flavors in wine. Armillaria mellea
is considered to be responsible for the presence of chloroanisoles in various origins of cork; however, no chloroanisole contamination was found in a recent study on Extremadura cork 
. The importance of the geographical origin of cork and the function of A. mellea
in the formation of chloroanisoles are still not completely clear. Some results 
showed that the fungi quantitative contamination was similar in TCA-contaminated and uncontaminated cork stoppers, but the number of the fungal species was higher in the last category. They observed that Paecilomyces
spp., Penicillium chrysogenum
, Penicillium glabrum
and Trichoderma viride
produced the highest quantity of TCA. Moreover, green fungi Pecilomyces
sp. and Penicillium chrysogenum
had the highest yields of conversion from TCP to TCA (17%–20%).
The contamination from different microorganisms can begin on trees and continue during wine storage, manufacturing and wine aging. Pesticides used on trees and cork stopper sanitizers containing chlorine compounds were identified as possible causes of contamination 
TCA production is caused by many fungi—Penicillium, Aspergillus, Actinomyces and Streptomyces—through the methylation of the corresponding 2,4,6-trichlorophenol, which can derive from chlorine-containing compounds in the cork, among other places. TCA and its precursors can be present in the atmosphere of the cellar coming from common sanitizers containing chlorine, which is why bleach—sodium hypochlorite—should not be used in wine cellars or neighboring environments.
Contamination with chlorophenols caused by fungicides or insecticides may involve woody materials used for the construction or lining of cellars, wooden pallets for bottles, paints, cartons and other materials that can be polluted by oenological adjuvants, bottles, corks and wines. TCA was also identified as a contaminant of oak barrels 
. In conditions of high humidity and limited ventilation, fungi can transform inodorous chlorophenols with high perception thresholds into chloroanisoles with low perception threshold. In these cases, TCA is not generally present, but it is more common to find 2,3,4,6-tetrachloroanisole (TeCA) with a moldy cellar odor and other molecules such as 2,3,4,6-tetrachlorophenol, 2,3,4,5,6-pentachloroanisole (PCA) and pentachlorophenol 
. Recently, a study proposed a method to evaluate chloroanisoles and chlorophenols in the cellar atmosphere, in the stoppers, in mini staves, in bottling areas and cap storage units 
. A review 
described analytical methods for quantification of haloanisoles and halophenols in the cork matrix. Another one 
discussed advances in the analysis of musty odor compounds in water and wine. A 2012 review 
focused on the analytical methods for cork-taint determination in wines. Other authors 
outlined the methods for chloroanisole determination using gas chromatography–olfactometry and they had a reliable positive response when TCA concentration was above 0.25 ng/L.
Odor detection threshold ODT is the lowest concentration at which a particular odorant is perceivable by the human sense of smell. Odor Recognition threshold: the concentration at which an odorant is not only detected but is also recognized by the human sense of smell (ISO 5492). However, it is difficult for wine tasters to correctly identify TCA in the wine at low concentrations due to fatigue of the sense organs, physiological sensitivities of each taster, professional experience and the influence of the substrate—which can vary the olfactory and gustatory perception of TCA. Its odor is generally described as mold, wet cardboard or mold cellar. As cited before, TCA has also been reported to be an olfactory suppressor of wine odor 
Different authors obtained various values of the TCA thresholds. Some assays 
showed that the substrate—type of wine—influences the TCA perception and recognition. In white wines the thresholds are generally lower (3–7 ng/L) than in the red wines (8–15 ng/L). If the wine is aged in wood, TCA recognition can be more difficult. Other results 
reported a TCA perception threshold of 4 ng/L in both neutral wines and dry white wines. In water, TCA perception thresholds range from 0.03 
to 1–2 ng/L 
for professional tasters or trained assessors.
It is difficult to determine a threshold to which consumers reject a contaminated wine—odor rejection threshold (ORT). An Australian study 
observed an ORT of 3.1 ng/L in a white wine, but some consumers had a very high threshold for TCA or do not deem it unpleasant. About 10% of consumers did not reject a wine with 32 ng/L of TCA. Others 
reported that a panel of consumers had an ORT of 10.4 ng/L for white wines and 16.0 ng/L for red wines, but ODT and taste detection threshold (TDT), respectively, for TCA were 0.2 and 0.3 ng/L in water, 0.9 and 1.7 ng/L for red wines, 1.5 and 1.0 ng/L for white wines and 4 and 10 ng/L for hydro–alcoholic solutions with 11.5% and 18% ethanol. This group of untrained assessors had very low ODT and TDT, but they did not reject the wine at these concentrations, even if their ORTs were lower. Generally, ODTs are lower than TDTs for TCA. A recent study 
shows the sensitivity of 34 panelists to some compounds responsible for off-flavor in wines and among them 2,4,6-trichloroanisole (TCA). A red wine—a de-aromatized, young, unwooded Shiraz wine—was added with 4 ng/L of TCA, but it was not significantly distinguished orthonasally from the same unpolluted wine.
2.2. 2,4,6-Tribromoanisole (TBA)
TBA is a highly volatile compound with a low perception threshold—0.5 µg/L in white wines—and an unpleasant odor of mold and mushrooms 
. It is produced by microorganisms from 2,4,6-tribromophenol (TBP)—a fireproofing agent that can easily spread in the atmosphere 
. TBA can contaminate wine during vinification, conservation and aging by being in contact with metal capsules treated with a paint containing brome resins or wood barrels and wood chips contaminated by TBA or TBP. Another source can be from air contamination caused by the presence of fireproofing agents containing TBA or TBP. Another source can be cork stoppers preserved in polluted environments. It has been found in wood barrels transported in in ships when containers were treated with fumigants containing brome 
. It has also been detected in samples of oak staves at a concentration of 8.9 ± 0.6 ng/g), which would contaminate wine 
Geosmin (trans-1,10-dimethyl-trans-9-decalol) is a sesquiterpene produced by various microorganisms including Bacteria, Protozoa, Actinomycetes, Blue Algae, Mushrooms and Molds (Penicillium
). Geosmin has a low perception detection threshold of 5 ng/L and an identification threshold of 10 ng/L in water 
The name, geosmin derives from Greek meaning odor (osmo
) of hearth (geo
). It smells of damp earth, humus, red beets, dump cellar and mold. It was first described as a river water pollutant but was soon found in wines made from grapes damaged or contaminated by Botrytis cinerea
and Penicillium expansum
. It is also a contaminant of foods, fruits, oak wood and cork stoppers. A sensory test with 137 operators of the oenological sector found cases of anosmia when tasting 5% geosmin in an aqueous solution 
The perception thresholds reported in literature vary from 30–45 ng/L with recognition thresholds from 50–65 ng/L, depending on the type of wine—lower in neutral white wines and highest in aromatic and red wines aged in wood. Geosmin created problems in some regions of France at the beginning of the 21st century 
. Its concentration does not change during the vinification since it is stable at the wine pH, but in order to lower its content by 50%, wine can be preserved at 20 °C for 2 months or at 10 °C for 8 months 
. Its presence is linked to Penicillium expansum
on grapes, but its production takes place on grapes prior to contamination by strains of B. cinerea 
Some environmental parameters such as water activity (aw) contribute to influence the physiology of Penicillium expansum
and Penicillium carneum
toward the production of geosmin 
. A cork defect detected at a sensory level by a trained panel in Austria was found to be due to geosmin contamination 
Treatments were proposed to reduce the concentration of geosmin based on grapeseed oil 
, sorption of enological yeasts 
and activated carbon 
The best solution to avoid these wine defects is the prevention, because the cure is not easy.
For grape contaminants, the only action to avoid them is to use healthy bunches or to select the cluster before vinification.
Recently, the risk to have chloroanisoles and chlorophenols in wines after grape storage or after the use of electrolyzed water in postharvest treatments was demonstrated 
In the case of other molecules. it is important to keep the wine cellar clean, the storage rooms of the bottles and the caps with sanitizers free of chlorine—and to limit the development of microflora by controlling humidity, ventilation and temperature. Moreover, it is suggested to choose suppliers with high quality controls and check the technical data not only of stoppers, but also for all possible causes of contamination such as dyes, lubricants, sanitizers, inks and pelliculants 
In other cases, the wine industry should avoid possible sources of chlorophenol pollution by checking for materials and furnishings that contain wood paints and fungicides before they are used in the construction of wine cellars and annexed rooms.
There is also a “Good practices guide for bulk wine transportation” developed by the International Wine Office (OIV) and adopted by its members States in 2000 
. It is based to a large extent on a previous guide published by the Wine and Spirit Association of Great Britain and Northern Ireland in 1994. The scope is to ensure acceptable cleanliness and freedom from any defect or contaminant which could adversely affect the characteristics or quality of the wine being carried, including its authenticity
. This advisory guide includes “procedures to which Suppliers and Purchasers on the one hand and Freight Forwarders and Ship Owners on the other, should refer when negotiating contracts concerning bulk wine transport operations. All the practices proposed, subject to their conformity with the applicable regulations in the various regions concerned, are in actual and successful use. With proper application, they contribute to the quality of the wine during transit and to guaranteeing its authenticity”
CELIÈGE or The European Cork Federation represents all the associations of cork producers which established the so-called SYSTECODE, an International Code of Cork Stopper Manufacturing Practice, an international reference for companies involved in production and sale of cork stoppers, but also for the users. On its web site (www.celiege.eu
) it is possible to verify the accredited companies of 7 countries (Portugal, Spain, France, Italy, Germany, Morocco, Tunisia) which can offer their customers a guarantee that their products comply with the standards since their production processes were checked ang analyzed objectively.
Generally, before use the cork stopper lots are submitted to a sensory test directly by the winemakers or with the support of a laboratory and the percentage of contaminated cork is defined. It is generally accepted a percentage of contamination of 2% for a cork stopper lot. If the percentage is higher the lot is rejected.
An Italian disciplinary 
was developed by various operators of the cork supply chain (Agris-Sardegna. Unione Italiana Vini, Assoimballaggi) and a university (Università Cattolica del Sacro Cuore, Piacenza, Italy) which shows the analytical methods for the control of the cork stoppers. This document gives indications also on the sensory control of cork stoppers before use.
Moreover, there are ISO norms concerning cork, specifically for cork-stopper sensory analyses (ISO 22308-2005).
Some experimental methods to remove some compounds, like geosmin, 1-octen-3-one and 1-octen-3-ol form contaminated wines were indicated in the previous sections, but none of them is allowed by U.E. law (Regulation EU 2019/934).
Researchers have proposed different experimental solutions to remove TCA—for example, a patent 
using activated charcoal obtained from carbons of coconut smells to “remove the cork taste and anomalous smells of cork materials”. Another patent 
proposes aliphatic synthetic polymers (ultra-high molecular weight polyethylene) to lower TCA from food and beverage products.
Highly absorbent yeast cell extracts 
were added to some wines (400 mg/L) stirred 3 times/day and with 2 days of contact. They were able to remove TCA (27%), TeCA (55%) and PCA (73%). The double dose gave better results: 45%, 73% and 83%, respectively. A dose of 100 mg/L could reduce TCA and TeCA content to concentrations lower than 5 ng/L and 25 ng/L, respectively.
The use of molecularly imprinted polymers and nonimprinted polymers were also experimented with good results: about 90% of TCA was removed 
The aforementioned study 
showed that plastic materials (polyethylene)—such as the lids of glass containers used to store wine samples—were also able to absorb chloroanisoles through direct liquid contact and via vapor. It was also showed that wine cask bladders and polyethylene film could remove TCA from wine.
All these solutions are not able to completely eliminate TCA and the quality of the wine is not totally preserved. Moreover, they can be expensive or experimented only at a laboratory scale.
In 2011 a cellular biosensor to detect TCA was proposed 
. It can quickly (3–5 min) detect TCA from cork soaks at very low concentrations of 1.02–12 ng/L), covering the whole range for the detection threshold for wines.
The most recent EU law (Regulation EU 2019/934) admits a treatment using a filter plate containing zeolites Y-faujasite only for the purpose to adsorb haloanisoles. It is subject to the conditions laid down in file 3.2.15 (2016) of the OIV Code of Oenological Practices 
: it can be applied during filtration to lower the concentration of haloanisoles responsible for off-flavor in wines, below their sensory perception threshold. This treatment should be carried out on clarified wines, the filter plates should be cleaned and disinfected before filtration and the application of zeolites Y-faujasite should comply with the prescriptions in the International Oenological Codex (Zeolite Y- faujasite, COEI-1-ZEOLIT:2016). This treatment is based on a patent 
Recently, it has been shown that some polymers (polyanilines) were able to eliminate 75% of TCA and 13% TBA in whisky without significative consequences on the aromatic profile and on the total phenolic content 
. The same team also verified the possibility to use these inexpensive polymeric materials as potential fining agents for elimination of TCA in the beverage industry, through a hybrid strategy of computational and experimental studies 
. These polymers seem to have some advantages for future practical applications.
Table 1 synthetizes the most important molecules involved in the so-called “cork taint” and the corresponding references cited in this review.
Table 1. The molecules involved in the so called “cork taint” and the references cited in this review.
||Fungi contamination of water, cork, cork stoppers, woody materials (oak barrels, pallets), paints, cartons, bottles, wines
||mold, damp cellar, wet cardboard
||Fungi or air contamination of water, wine, wood barrels or chips, cork stoppers
||Various microrganisms contamination of water, grapes, oak wood, and cork stoppers
||damp earth, humus, red beets, mold, dump cellar
||Actinomycetes contamination of cork or B. cinerea affected grapes
||earthy, mushroom, damp earth, camphor
||Bacteria (Streptomyces) contamination of cork and wood barrels or “smoke taint”
||smoked, phenolic, medicine
|Mushrooms contamination of cork stoppers, wood barrels or B. cinerea affected grapes
||fresh mushrooms and metal
||Rhizobium excellensis contamination of cork bark
||earthy, herbaceous, potato, unripe hazelnut, dirty
|3-isobutyl-2-Methoxyipirazine (IBMP), 3-Sec-butyl-2-methoxyipirazine (SBMP), 3-isopropyl-2-Methoxyipirazine (IPMP)
||Contaminated cork stopper, undesired insects (Harmonia axyridis) presence during fermentation
||green pepper, peas, potatoes