Black tea brewed is best (4)
I believe the answer is:
beat
'is best' is the definition.
(I've seen this before)
'black tea brewed' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'brewed' indicates an anagram.
'tea' is an anagram of 'eat'.
'b'+'eat'='BEAT'
(Other definitions for beat that I've seen before include "Defeat; pulsate" , "Policeman's round" , "course run regularly" , "Throb; surpass" , "Thrash with rhythm?" .)