Spumante source (4)
I believe the answer is:
asti
'spumante source' 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 "Italian white wine" , "Piedmont wine city, SE of Turin" , "Sparkling wine named after an Italian Piedmont town" , "town in Italy" , "18" .)