It's a flipping sparkling wine (4)
I believe the answer is:
asti
'sparkling wine' is the definition.
(Asti is a type of sparkling wine)
'it's a flipping' is the wordplay.
'flipping' is a reversal indicator.
'its'+'a'='itsa'
'itsa' back-to-front is 'ASTI'.
(Other definitions for asti that I've seen before include "Italian town, famous for its wine" , "Fizzy wine" , "Capital of a north-west Italian province, known for its sparking wine" , "Sparkling drink" , "18" .)