Head of the brewery? (4)
I believe the answer is:
foam
'head of the brewery?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for foam that I've seen before include "Fizz, froth" , "Lather, froth" , "Froth created by wave or soap" , "At the mouth, this may mean madness or extreme anger" , "Suspension of gas in a liquid" .)