Sour, turned (3)
I believe the answer is:
off
This clue is a double definition.
'sour' is the first definition.
(I know that sour can be written as off)
'turned' is the second definition.
(I know that turned can be written as off)
(Other definitions for off that I've seen before include "Gone - bad" , "Unsatisfactory" , "Away, at a distance" , "Disappointing" , "Not working - started" .)