I say wine brought about the onset of indigestion — very acidic (9)
I believe the answer is:
corrosive
'acidic' is the definition.
(thesaurus)
'i say wine brought about the onset of indigestion very' is the wordplay.
'i say' becomes 'cor' (both are expressions of surprise).
'wine' becomes 'rose' (rose wine is a kind of wine).
'brought about' is an insertion indicator.
'the onset of' indicates taking the first letters.
The first letters of 'indigestion very' is 'iv'.
'rose' enclosing 'iv' is 'rosive'.
'cor'+'rosive'='CORROSIVE'
(Other definitions for corrosive that I've seen before include "Destroying by chemical action" , "Hurtful" , "Caustic, erosive" , "Able to eat away" , "Caustic and destructive" .)