Italian sparkler (4)
I believe the answer is:
asti
'italian sparkler' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asti that I've seen before include "18" , "It's a (anag) - wine" , "Source of fizz" , "Bubbly wine" , "Piedmontese white wine" .)