Wine, when it is from the east (4)
I believe the answer is:
asti
'wine' is the definition.
(Italian wine)
'when it is from the east' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'is from the east' is a reversal indicator (on a map from right to left).
'it' written backwards gives 'ti'.
'as'+'ti'='ASTI'
(Other definitions for asti that I've seen before include "Capital of a north-west Italian province, known for its sparking wine" , "Sparkling drink" , "18" , "Piedmontese white wine" , "Italian white wine" .)