Quercus project: preliminary results discussed - study of cork industry - Industry Overview

In 1993 the European Cork Industry Federation (CELIEGE) in cooperation with the EEC undertook a detailed study of the cork industry. The project, titled "Quercus", combined the efforts of nine laboratories in six countries. The object was to identify the sources of off-flavors associated with cork stoppers and develop a strategy to correct them.

On Friday, November 22, preliminary results of the Quercus project were released in Paris. A detailed summary and a compendium of recommended industry practices will be forthcoming in the next few months. A brief review of some of the findings presented at the Paris meeting are shown below.

Numerous compounds were examined as causes for off-flavors in wine. The most prominent, 2,4,6-trichloroanisole (TCA), was determined to be present in the majority of wines described as exhibiting a musty taint. Samples of "off-flavor or musty" wines exhibited the presence of TCA in 65% of the bottles analyzed. This finding corroborates a large body of literature linking TCA to off-flavors in wine and other food products. A by-product of this sensory analysis was the construction of a standardized flavor wheel that allowed the different laboratories to better coordinate their sensory categorizations of corks.

With TCA identified as the major target, each individual component of the cork processing method was examined for particular susceptibility to its formation. The analysis has yielded a body of work that is the basis for a protocol of recommended practices for cork manufacturers.

The findings concluded that the single greatest correlation for TCA in finished corks was the relative level of TCA in the original raw bark. A review of TCA occurrence in the forest showed a high incidence of TCA in bark marked with the relatively rare, but easily identified condition "yellow stain". Slight increases in TCA were also found in the bark closest to the ground. Specific precautions to avoid the high-risk materials are included in the protocol of recommended practices.

Studies of the manufacturing process did not find specific areas that were prone to the introduction of TCA. There was a conclusion that finished corks prepared with a chlorine-based wash contained significantly higher levels of residual chlorophenols. Since one proven source of TCA is the metabolism of chlorophenols by certain fungi, the presence of chlorophenols is considered undesirable.

Studies of storage conditions were conducted under two models. The first tested the ability of TCA to migrate from a highly-contaminated environment through a cork stopper in a finished wine bottle. Tests did not show any conclusive evidence of such migration even after nine months of storage.

The second model tested the likelihood of TCA being transmitted from a highly-contaminated environment to cork stoppers under typical warehouse storage conditions. Tests showed that one week of storage in a highly-contaminated environment produced significant contamination. When used in bottling, the contaminated corks "leached" TCA into the bottled wine at levels consistent with commercial samples of tainted wines (approx. 6ppt). The same test was performed with wine bottles in warehouse storage conditions. They also became contaminated after one week of storage, and when used with clean corks, produced high TCA levels (approx. 170ppt). The difference in relative concentration was attributed more to the relative surface areas of the bottle compared to the cork. Industry guidelines governing storage practices are a major focus of the study.

The complete body of evidence will be used to prepare a protocol of manufacturing practices that will specify techniques governing the selection and storage of raw bark, particular manufacturing practices and final preparation and shipping practices. Early in 1997 members of CELIEGE will present the detailed results of project QUERCUS at a U.S. location.

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