Journalist on the beer (8)
I believe the answer is:
reporter
'journalist' is the definition.
(eg a reporter for a newspaper)
'on the beer' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'the beer' becomes 'porter' (type of beer).
're'+'porter'='REPORTER'
(Other definitions for reporter that I've seen before include "He gives details" , "One writes or tells the news" , "Hack" , "One who writes the news for the media" , "News gatherer" .)