Ours turned bitter (4)
I believe the answer is:
sour
'bitter' is the definition.
(I've seen this in another clue)
'ours turned' is the wordplay.
'turned' is an anagram indicator.
'ours' with letters rearranged gives 'SOUR'.
(Other definitions for sour that I've seen before include "Tart, acidic" , "Having an acid taste or smell" , "Acetic" , "Acid or caustic" , "Acid-tasting" .)