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.

One of my favorite homebrews was made with hojicha. I’ve made it a few times.

I tried using pu-er, but it didn’t do much. 100g in 30l was just too little to make a bigger difference.

I think that I throw it in boil for last 10 minutes. Final beer was little bit darker.