Brown grape's initial flavour (4)
I believe the answer is:
tang
'flavour' is the definition.
(I know that flavour can be written as tang)
'brown grape's initial' is the wordplay.
'brown' becomes 'tan' (tan is a kind of brown).
'initial' indicates taking the first letters.
The first letter of 'grapes' is 'g'.
'tan'+'g'='TANG'
(Other definitions for tang that I've seen before include "Savour" , "Pungency" , "Strong taste; Chinese dynasty" , "tastefulness" , "Strong flavour" .)