A white pawn (4)
I believe the answer is:
hock
I believe this clue is a double definition.
'a white' is the first definition.
(type of white wine)
'pawn' is the second definition.
('hock' can be a synonym of 'pawn')
(Other definitions for hock that I've seen before include "Leg joint on horse e.g." , "Buy property, say" , "White wine and horse's joint" , "Pawn; white wine" , "Pawn < some ham" .)