I always thought that tannin was an organic substance that was used in leather tanning (hence the name, I guess), dyeing, and making ink. I suppose, being an organic substance, it could also be an ingredient in tea. However, if both of the above statements are true, I may never drink tea again.

Oh, yea -- doesn't tannin have some significance for werewolves? Something in the one of the far corners of my mind whispers werewolf whenever I hear tannin.