Sibyl's about to down a litre twice — of these? (4,4)
I believe the answer is:
real ales
'twice of these?' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'sibyl's about to down a litre' is the wordplay.
I cannot quite see how this works, but
'about' could be 'rea' (I've seen this in other clues) and 'rea' is found in the answer.
'a' is found in the answer.
'litre' could be 'l' (abbreviation) and 'l' is present in the answer.
The remaining letters 'les' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for real ales that I've seen before include "Traditional beers" , "traditional drinks" .)