Ferment (4)
I believe the answer is:
brew
'ferment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for brew that I've seen before include "Make beer by boiling and fermentation" , "Prepare (drink of tea)" , "Infusion" , "Prepare by boiling and infusing" , "Ferment rather than distil" .)