title_body: How can I add post-flavoring to beer?
upvoted_answer: Any time you mix things into beer you'll lose some carbonation. Any powder would nucleate bubbles very quickly, so the flavoring should be in liquid form. The liquid should be as similar to beer possible: cold, equally carbonated, and not too much alcohol if it can be avoided. Stir gently in a cold glass and serve right away.
  
  Or, if you are brewing the beer yourself just add it at kegging or bottling time.