Remove blemish in beer (5,3)
I believe the answer is:
strip out
'remove' is the definition.
(I've seen this before)
'blemish in beer' is the wordplay.
'blemish' becomes 'rip' (a rip is a blemish or tear in fabric).
'in' is an insertion indicator.
'beer' becomes 'stout' (I've seen this before).
'rip' put inside 'stout' is 'STRIP OUT'.
(Other definitions for strip out that I've seen before include "Take items from balance sheet" , "Remove (items) from a balance sheet" .)