not sure if have already brewed. i have used pb2 twice (oatmeal peanut butter chocolate stout)
the first beer i used it both in the boil and secondary. in that beer i just dumped the jar in the secondary (along with cacao nibs 1jar/6gals). i noticed no off flavors. however, nearly every bottle was way overcarbed. the second beer i just made about 2 months ago. in the recent batch i just add the PB2 to the boil, non of the beer were overcarbed. Both beers tasted fine.