I have heard of people making a kind of lemonaide type drink from sumac, they have little hairs on them that have something slightly toxic, oxalic or prussic acid, something obnoxious, that has to be dealt with before drinking. Always sounded like a lot of work and you wouldnt know if you did it right until you drank it and seen if your throat closed up
There are so many other tannin sources that are so much easier to use, like crab apples, or oak, or winemaking tannins. But sumac is a legitimate wild food if you if you know how to prepare it, but would the acids outweigh its contribution of tannins? WVMJ