Unique beer catches on (5)
I believe the answer is:
alone
'unique' is the definition.
(I've seen this before)
'beer catches on' is the wordplay.
'beer' becomes 'ale' (I've seen this before).
'catches' indicates putting letters inside.
'ale' placed around 'on' is 'ALONE'.
(Other definitions for alone that I've seen before include "Note of charges" , "without another" , "Lacking company, solitary" , "Isolated from others" , "Singly" .)