Bitterness

Not a flavour you want or expect to find in wine, bitterness should not be confused with a feeling of astringency, which comes from tannin. If a wine tastes unpleasantly bitter, it might be a sign of a fault, and could be turning to vinegar. Vinegar-flavoured wine is irrevocably faulty. Occasionally, you may detect a touch of bitter oak flavour in the wine, which means that the oak barrel in which it was aged has not been properly seasoned, but this is uncommon.