Intellectual emptying beer into breakfast! (8)
I believe the answer is:
cerebral
'intellectual' is the definition.
(I know that intellectual can be written as cerebral)
'emptying beer into breakfast' is the wordplay.
'emptying' suggests removing the centre.
'into' means one lot of letters goes inside another.
'breakfast' becomes 'cereal' (I've seen this before).
'beer' with its centre removed is 'br'.
'br' inserted into 'cereal' is 'CEREBRAL'.
(Other definitions for cerebral that I've seen before include "Relating to the brain" , "Of the brain, intellectual" , "Concerning the brain" , "Highly intellectual" , "Intellectual, brainy" .)