It's instrumental in making a brand of beer, 'Devil's Head Grog' (4,4)
I believe the answer is:
bass drum
'it's instrumental' is the definition.
(bass drum is a kind of musical instrument)
'a brand of beer devil's head grog' is the wordplay.
'a brand of beer' becomes 'bass' (Bass is a brand of beer).
'head' says to take the initial letters.
'grog' becomes 'rum' (I've seen this in another clue).
The initial letter of 'devils' is 'd'.
'bass'+'d'+'rum'='BASS DRUM'
'in making' is the link.
(Other definitions for bass drum that I've seen before include "Deep instrument" , "Big percussion instrument" , "musical instrument" , "Booming percussion instrument" , "Large percussion instrument" .)