I know some add tannins to balance out flavour profiles, but this is done with extracts closer to bottling from hazy recollection. Reddit’s u/stormbeforedawn often propounds a metaphor of flavour as a table with three legs; Acid, sugar, and tannin. If these are carefully leveled against one another, a balanced flavour profile will be achieved.

Black tea is a good source of tannin, but so are toasted woods. I recall that spirals of wood are considered superior to chips, but I can’t recall why. This is all off the top of my head at the moment. Hope I’ve at least given you some breadcrumbs to follow.