So I've got the B3 Oatmeal Stout Partial Mash recipe and i was thinking of adding something. Either Vanilla or Chocolate. How much chocolate would I want to add. I have no access to a LHBS, so its either cocoa powder or Vanilla extract. I've seen 8oz of cocoa powder at 15 mins or 4oz at 30 and 4 at 15. Does it really matter?