If you want to add coffee to a batch of brew, buy 4oz of freshly course ground beans (like dark/french roast) and cold brew it about 12 hours. Add the liquid to taste either in the keg or bottling bucket.
Exposing coffee to heat (like in hot water) causes the extraction of acids that give it a somewhat bitter flavor. Over time, that becomes an astringent, stale, bitter flavor.
Good Temp Control -----> Happy Yeast ------> Tasty Brew