The yellow spot is a visual defect that appears in cork corks and spreads from the surface of the bark to the interior. The corks affected by this defect are located in humid areas with abundant undergrowth, conditions that occur in the forests of Catalonia. The appearance of this defect is due to the growth of the pathogenic fungus Armillaria mellea.

The presence of a yellow spot on the cork goes beyond being a visual defect given that it is considered to be the main responsible for the presence in some corks of 2,4,6-trichloroanisole (TCA) or a compound that gives the wine its flowery aroma . For this reason, the panels affected with this defect leave the production chain and are treated as forest waste. The economic losses associated with the presence of TCA in corks affect the entire value chain: forest owners, cork and wine industry. The incidence of TCA in corks has led to the emergence of campaigns at international level against the use of cork. The result of these actions has been the loss of value of corks and corks and the abandonment of cork management. In general, the incidence of yellow spot has led to a significant loss of raw material, especially with regard to cork of Catalan origin.

Currently, there are few studies on the conditions that favor the infection of cork oaks by Armillaria mellea and therefore, on the possible actions to prevent and/or eliminate this pathogen. At the same time, the real incidence of this defect is unknown and there are no recent studies confirming the most affected areas. The relationship between the presence of yellow stain and the formation of TCA is another aspect that should be contrasted in order to be able to define the implications of its presence in corks, and assess whether its elimination is possible. The lack of knowledge about this defect is possibly the main reason why until now no guidelines have been described for its prevention, nor developing technologies for its detection and/or elimination.