Wine, mostly red — sat in getting drunk (7)
I believe the answer is:
retsina
'wine' is the definition.
(retsina is a kind of wine)
'mostly red sat in getting drunk' is the wordplay.
'mostly' means to remove the last letter.
'getting drunk' indicates anagramming the letters.
'red' with its final letter taken away is 're'.
'sat'+'in'='satin'
'satin' anagrammed gives 'tsina'.
're'+'tsina'='RETSINA'
(Other definitions for retsina that I've seen before include "S European wine" , "Oily-tasting Greek white wine" , "Greek white wine flavoured with resin" , "Type of Greek wine" , "Flavoured Greek white wine - nastier brand" .)