Italian white jacket's taken off over the hill (4)
I believe the answer is:
asti
'italian white' is the definition.
(Italian white wine)
'jacket's taken off over the hill' is the wordplay.
'jacket's taken off' indicates the central letters (the letters which clothe the word are removed).
'over the hill' becomes 'pastit' ('past it' and 'over the hill' can both mean ageing).
The middle of 'pastit' is 'ASTI'.
(Other definitions for asti that I've seen before include "Fizzy wine" , "Italian town, famous for its wine" , "Capital of a north-west Italian province, known for its sparking wine" , "town in Italy" , "- spumante, It. wine" .)