Briefly drink black stuff, a delicious beverage (6)
I believe the answer is:
nectar
'a delicious beverage' is the definition.
'briefly drink black stuff' is the wordplay.
'briefly' means to remove the last letter.
'drink' becomes 'neck' (to neck a drink is to drink it quickly).
'black stuff' becomes 'tar' (tar is a black substance).
'neck' with its last letter taken off is 'nec'.
'nec'+'tar'='NECTAR'
(Other definitions for nectar that I've seen before include "Sugary stuff in plants to attract insects" , "Heavenly brew" , "Recant (anag.)" , "Sugary secretion" , "Ambrosia" .)