Sour stuff puts five in rage, unfortunately (7)
I believe the answer is:
vinegar
'sour stuff' is the definition.
(I've seen this before)
'five in rage unfortunately' is the wordplay.
'five' becomes 'V' (Roman numeral).
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'rage' is an anagram of 'egar'.
'v'+'in'+'egar'='VINEGAR'
'puts' acts as a link.
(Other definitions for vinegar that I've seen before include "bad wine?" , "Acidic condiment" , "Pickling medium" , "Sourish liquid for flavouring chips" , "Pickling condiment" .)