Drain Armagnac, then free bitter (5)
I believe the answer is:
acrid
'bitter' is the definition.
(I know that bitter can be written as acrid)
'drain armagnac then free' is the wordplay.
'drain' suggests removing the centre (I've seen 'drained' mean this).
'then' is a charade indicator (letters next to each other).
'free' becomes 'rid' (to be free of something is to be rid of it).
'armagnac' with its middle taken out is 'ac'.
'ac'+'rid'='ACRID'
(Other definitions for acrid that I've seen before include "Pungent; caustic" , "Unpleasantly bitter" , "Bitter in smell, like smoke" , "Having a bitter taste or small, like smoke" , "Sour, pungent" .)