First to nag about strong flavour (4)
I believe the answer is:
tang
'strong flavour' is the definition.
(I've seen this before)
'first to nag about' is the wordplay.
'first to' becomes 't' (1st letter of 'to').
'about' indicates an anagram.
'nag' with letters rearranged gives 'ang'.
't'+'ang'='TANG'
(Other definitions for tang that I've seen before include "relish" , "Strong, pungent taste" , "Strong flavour" , "Piquancy - Chinese dynasty" , "Savour" .)