I think you'll be ok. It will mellow with time. It will mellow at room temps faster than it will cold. When I did the coffee addition to one of my beers I cold steeped 1cup of coffee grinds in 4cups of water In the fridge for a few days then poured it through a coffee filter in a strainer then added it to the bottling bucket/keg. It came out with pretty good results.
Beer Plus Science = .....Good!!!!! By: Adam Savage