Serves up the foreign beer endlessly from the very start of speech (6)
I believe the answer is:
verbal
'speech' is the definition.
(thesaurus)
'serves up the foreign' is the wordplay.
'serves' becomes 'verb' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'the foreign' becomes 'la'.
'la' backwards is 'al'.
'verb'+'al'='VERBAL'
'beer endlessly from the very start of' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for verbal that I've seen before include "Spoken, oral" , "Spoken (abuse)" , "Relating to words" , "Communicated in words" , "Expressed in words" .)