Corked wine under screwcap?

Monday, 3 June, 2019
Dr. Carien Coetzee
Mouldy or musty aroma in a wine is probably the most unpleasant oenological defect. It is mainly caused by the presence of compounds called haloanisoles (HA). Corks have been singled out (rather unfairly) as being the main source of HA in wine (“cork taint”), and although the cork is a major contributor, it certainly is not the only cause.

Wines under screwcap and wines packaged using bag-in-box has also been reported to occasionally harbour this fault. So how did these wines come to be contaminated with “cork taint” if it has never been in contact with cork?

First, it is important to understand how this fault arises. TCA (2,4,6-trichloroanisole) is the most prevalent HA in “corked” wines, however, studies have shown that it only accounts for about 50% of the wines flagged with mouldy aroma2. Other compounds such as TeCA (2,3,4,6-terachloroanisole), PCA (pentachloroanisole), TBA (2,4,6-tribromoanisole), geosmine, 2-methoxy-3,5-dimethylpyrazine, 1-octen-3-one, 1-octen-3-ol and 2-methylisoborneol can also contribute significantly to earthy, mouldy, musty, mushroom and muddy aroma1,3,4. Any of these compounds, all with very different chemical make-up, can be the source of the defect, it is therefore important to rely on the sensory evaluation of wine (and not only chemistry) as the principle method to confirm the defect.

Haloanisoles form due to a biochemical reaction initiated by several kinds of microorganisms, most notably filamentous fungi (mould)5. The fungi on its own will not be able to form HA. It needs a source of chlorine or bromine that it can metabolize to generate the odoriferous HA. This source is usually in the form of halophenols and are the precursor compounds that the microorganism uses to form HA. Therefore, two factors are key here: 1) the presence of the fungi and 2) contact with precursor.

Sources of chlorine/bromine containing precursors

Chemical products containing chlorine and/or bromine are widely employed in industrial processes. Halophenols are (non-odoriferous) compounds that are often used for the preservation of wood, cardboard, paint, vegetable fibers, textile goods, leathers and more. In a cellar, these precursors can originate from treated wood structures (walls, floors, ceilings) or other wood-based winemaking equipment such as barrels, wood cases, palettes and wooden stands for bottle storage.

The precursors are also widely used as herbicides, fungicide and insecticide and although the use of several of these compounds has been forbidden for many years by some countries, there are still a number of potential precursors regularly used as pesticides. Other than that, many of these precursors can manifest in the environment for a very long time (even decades), therefore the discontinuation thereof does not necessarily remove the compounds.

Another source of precursors is water. Pesticides in water and the disinfectant treatment of water can lead to the formation of these precursors, which can then be transferred to the cork or other fungi-containing substances.

The industrial use of these chemicals is thus probably the main source of precursors and consequently, HA in wine1.

The role of the cork

Cork is a very complex microbial ecosystem and during the initial stages of the manufacturing process, it can contain very large microbial populations including bacteria and fungal strains5. These populations decrease rapidly, and the final cork usually contains a very low presence of microorganisms.

Consider the presence of microorganisms: If the cork is then exposed to the halophenol precursors from the environment, then the fungi can produce HA. This can occur during manufacturing, before bottling or even after bottling (as long as both factors are present).

The contamination of the cork while it is still in the forest is also a possibility. Contact with the precursors at this stage can lead to the formation of the HA already in the premanufacture stages. In this case, the cork will be a direct source of HA when it arrives at the cellar.

Cork also has a high capacity to absorb the HA from a contaminated environment; therefore, the cork can arrive at the cellar clean, but absorb HA from polluted material and later transfer it to the wine. In this case, the cork merely serves as a transmitter.

Contamination before bottling

As mentioned previously, the treatment of wood with the halophenol precursors can be a significant source of HA. With the presence of the fungi in the wood, significant amounts of HA can be formed and transferred (even through air!) to wine stored in tanks or barrels. You only need a small amount of these compounds to manifest the taint and even if these wooden structures/elements are removed, the precursors and/or HA can adsorb in the microporous winery structure (other building material) and be released over time contaminating new winery equipment6.

Products used during the wine production process (bentonite, filter powder etc) can also absorb the precursors and HA from the direct environment and be transferred to the wine during treatment. 

It is therefore of paramount importance to keep the cellar environment completely devoid of any potential precursors.

How do you know where the taint came from?

This is the tricky part. There is no definite way to determine where exactly the taint derived from. Obviously, when a wine packaged under screw cap or bag-in-box, then (unless there are some serious packaging issues) the cellar environment will be the source of the taint. The next element to investigate is bottle differences. If there is large variation between the bottles (of the same batch of wine), then there is a high probability that the of the cork is the source of the problem, or at least, part of the problem. The possibility of a mixed contamination (cellar environment and the cork) also exists.

So yes, in many cases the cork is the guilty party contaminating perfectly good wine, but in some cases it has been dubbed culprit unfairly. The erroneous term “cork taint” should perhaps be replaced by “fungal taint” unless it can be well demonstrated that the stopper is the primary source of contamination.


(1)       Rubio Coque, J. J.; Pérez, E. R.; Goswami, M.; Martínez, R. F.; García, S. C.; Álvarez Rodríguez, M. L.; Martín, J. F. M. Wine Contamination by Haloanisoles: Towards the Development of Biotechnological Strategies to Remove Chloroanisoles from Cork Stoppers; Inbiotec, 2006.

(2)       Soleas, G. J.; Yan, J.; Seaver, T.; Goldberg, D. M. Method for the Gas Chromatographic Assay with Mass Selective Detection of Trichloro Compounds in Corks and Wines Applied To Elucidate the Potential Cause of Cork Taint. J. Agric. Food Chem.2002, 50 (5), 1032–1039.

(3)       Amon, J. M.; Smilanick, J. L.; Vail, P. V; Hartsell, P. L.; Gómez, E. Compounds Responsible for Cork Taint. Austral. N.Z. Wine Ind. J.1989, 4, 62–69.

(4)       Lee, T. H.; Simpson, R. F. Microbiology and Chemistry of Cork Taints in Wine. In Wine Microbiology and Biotechnology; Fleet, G. H., Ed.; Harwood Academic Publishers: Chur, Switzerland, 1992; pp 353–372.

(5)       Alvarez-Rodriguez, M. L.; Lopez-Ocana, L.; Lopez-Coronado, J. M.; Rodriguez, E.; Martinez, M. J.; Larriba, G.; Coque, J.-J. R. Cork Taint of Wines: Role of the Filamentous Fungi Isolated from Cork in the Formation of 2,4,6-Trichloroanisole by O Methylation of 2,4,6-Trichlorophenol. Appl. Environ. Microbiol.2002, 68 (12), 5860–5869.

(6)       Chatonnet, P.; Bonnet, S.; Boutou, S.; Labadie, M.-D. Identification and Responsibility of 2,4,6-Tribromoanisole in Musty, Corked Odors in Wine. J. Agric. Food Chem.2004, 52 (5), 1255–1262.