Face fine when brewing stimulant (8)
I believe the answer is:
caffeine
'stimulant' is the definition.
(I've seen this before)
'face fine when brewing' is the wordplay.
'when brewing' is an anagram indicator.
'face'+'fine'='facefine'
'facefine' with letters rearranged gives 'CAFFEINE'.
(Other definitions for caffeine that I've seen before include "Fine face (anag.)" , "Stimulant found in mug or cup?" , "Stimulant in tea, etc" , "Stimulant in, eg, cappuccino" , "Stimulating substance found in fine cafe, oddly" .)