It’s a retrograde sparkling wine (4)
I believe the answer is:
asti
'sparkling wine' is the definition.
(I've seen this before)
'it's a retrograde' is the wordplay.
'retrograde' shows that the letters should be reversed in order.
'its'+'a'='itsa'
'itsa' back-to-front is 'ASTI'.
(Other definitions for asti that I've seen before include "Source of fizz" , "Alcohol" , "Piedmontese white wine" , "It's a (anag) - wine" , "Sparkling wine named after an Italian Piedmont town" .)