Brought up beer: a mistake (4)
I believe the answer is:
slip
'a mistake' is the definition.
(a slip is a blunder or mistake)
'brought up beer' is the wordplay.
'brought up' says the letters should be written in reverse (in a down clue, letters go up).
'beer' becomes 'pils' (Pilsner beer).
'pils' in reverse letter order is 'SLIP'.
(Other definitions for slip that I've seen before include "Fall or make a small mistake" , "Mistake (of tongue or pen)" , "shift" , "Fail < to engage gear" , "Faulty" .)