Theresa Heredia  

The Cork Problem

Cork-taint imparts a musty/moldy off-flavor in finished wine and is considered a defect. The problem is related to the cork closure, made from the bark of the cork oak, Quercus suber, thus giving rise to the name “cork-taint”(1). The magnitude of the off-flavor imparted by TCA is variable and is dependent upon wine type, TCA concentration, and the individual tasting the wine. In cases of mild taint, the fruity character tends to be masked by a musty odor. In more severe cases, the characteristic aromas of the wine tend to be completely masked by a dank, moldy, earthy and sometimes medicinal odor.

The estimated incidence of cork-tainted wine bottles ranges from 2 – 7%. At a conservatively estimated taint rate of 2%, the estimated costs of using cork stoppers as wine bottle closures amount to $281 million a year in the United States alone (2).

Table 1: Cork Taint and its Impact on the US Wine Industry:

Statistics        Cost Per Year

US cork stopper imports    900,000,000/Year
Average price        $90/1000
Import value of corks    $81,000,000/year
Est. cork taint rate    2%
Est. value of tainted wine    $200,000,000/Year
Est. costs for cork closures    $281,000,000/Year
U.S. wine exports    $326,000,000/Year

The above table was adapted from Butzke et al., 1998(2)

The use of synthetic corks, screw caps and agglomerated natural corks as opposed to natural, standard one-piece corks have been reported, but many winemakers believe that the use of anything but a natural one-piece cork draws away from the aesthetic appeal of the wine. The only alternatives are to reduce the defective rate of natural corks by improving the processing protocol at the manufacturing stage and to facilitate easier sampling and analysis of corks by wineries at the cork consumer end.

Due to its implication in cork taint, the chemical behavior of TCA in wines and corks has been studied extensively. A reliable, quantitative method for the extraction of TCA from wines has been established but a reliable method for extraction of TCA from corks has, until now, not been established. Having reliable, quantitative methods for extraction of TCA from both wines and corks will allow further investigation into the chemical and physical behavior of TCA in bottled wines. With a good understanding of this complex behavior and a transfer of this knowledge to the cork-producing and wine industries, it will be easier to apply methods to reduce the incidence of cork taint and its impact on the economies of all wine producing regions.

Conclusion

The investigations into TCA and related cork taint compounds have established invaluable methods for the analyses of these compounds and the results obtained have provided a tremendous amount of knowledge with respect to their chemical behavior. The availability of reliable, quantitative methods for the extraction of TCA from both wines and corks will allow further investigation into the chemical and physical behavior of TCA in bottled wines. A good understanding of the complex behavior of TCA and the related taint compounds will make it easier to employ methods to reduce the incidence of cork taint in all wine producing regions.