Saturday fliers imbibing upper-class drink? (9)
I believe the answer is:
sauternes
'drink?' is the definition.
(Sauternes is an example)
'saturday fliers imbibing upper-class' is the wordplay.
'saturday' becomes 'sat' (short for Saturday).
'fliers' becomes 'ernes' (erne is a kind of bird).
'imbibing' means one lot of letters goes inside another.
'upper-class' becomes 'u' (similar in meaning).
'sat'+'ernes'='saternes'
'saternes' enclosing 'u' is 'SAUTERNES'.
(Other definitions for sauternes that I've seen before include "Sweet French wine" , "Sweet white wine" , "A sweet Bordeaux" .)