Baker's ingredient (5)
I believe the answer is:
yeast
'baker's ingredient' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yeast that I've seen before include "Substance used to raise dough etc" , "It makes dough rise" , "Fungus used in fermenting" , "Beer froth agent" , "It's put in to raise" .)