Up, mostly making wine (4)
I believe the answer is:
asti
'wine' is the definition.
(I've seen this before)
'up mostly' is the wordplay.
'up' becomes 'astir' (synonyms).
'mostly' means to remove the last letter.
'astir' with its last letter taken off is 'ASTI'.
'making' is the link.
(Other definitions for asti that I've seen before include "Italian 'sparkler'" , "Italian town, famous for its wine" , "Piedmont wine city, SE of Turin" , "Sparkling wine named after an Italian Piedmont town" , "18" .)