Brewing ingredient? It's put back in still (5)
I believe the answer is:
yeast
'brewing ingredient?' is the definition.
(ingredient used in brewing alcohol)
'it's put back in still' is the wordplay.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'put back' says the letters should be written in reverse.
'in' is an insertion indicator.
'still' becomes 'yet' (synonyms).
'sa' written backwards gives 'as'.
'as' put inside 'yet' is 'YEAST'.
(Other definitions for yeast that I've seen before include "lifting agent" , "Dough-raising agent" , "Fungus used to ferment sugar" , "It's put in to raise" , "Baker's ingredient" .)