Best black tea brewed (4)
I believe the answer is:
beat
'best' is the definition.
(I've seen this before)
'black tea brewed' is the wordplay.
'black' becomes 'b' (abbreviation 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 "Throb; surpass" , "Do better than another in competition" , "tired" , "Thrash, punish physically" , "Policeman's round" .)