If a wine tastes like corks, this is mainly due to trichloro anisole, a compound that is released by certain corks. But chemists have discovered other molecules that come into contact with the cork when the wine ages. Analyzes showed that secondary plant substances, called polyphenols, migrate from the cork into the wine, where they change the bouquet (the scent), the taste and the astringency (the bitter mouthfeel) – for better or for worse.
Sofia Reis, Victor Freitas and their colleagues from the University of Porto in Portugal have resumed these analyzes and followed the changes in the tannins, i.e. the tannins, as they described in the “Journal of Agricultural and Food Chemistry” in 2020.
series »Culinary Laboratory«
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The main components of wine include the polyphenols already mentioned, including the flavonoids from grapes. But others come from the wood of the barrels, especially the tannins, which add to the bitterness or tartness by combining with the proteins in saliva.
The corks also release substances. The Portuguese chemists discovered that in an alcoholic, acidic solution similar to wine, other substances appeared after just 24 hours of contact with the cork: castalagin, vescalagin, grandinin and roburin. All of them are tannins, i.e. tannins, which mostly owe their name to the wood in which they were first found, such as oak or chestnut.
But why were only small amounts of these tannins found in older experiments that lasted 27 months? Were they overlooked in the first analysis that focused primarily on the polyphenols? Undoubtedly, because a 2019 study on tannins found the same compounds in corks and in the ethanolic extracts of corks.