Dough-rising ingredient (5)
I believe the answer is:
yeast
'dough-rising 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 "Brewer's agent" , "Leavening agent in bread-making" , "Beer froth agent" , "Rising agent" , "A raising agent in baking" .)