The old sat, ordering bread ingredient (5)
I believe the answer is:
yeast
'bread ingredient' is the definition.
(I've seen this in another clue)
'the old sat ordering' is the wordplay.
'the old' becomes 'ye' (resembles a historical spelling of 'the').
'ordering' is an anagram indicator.
'sat' with letters rearranged gives 'ast'.
'ye'+'ast'='YEAST'
(Other definitions for yeast that I've seen before include "Leavening agent in bread-making" , "Substance used in brewing and baking" , "Fungus; food supplement" , "that baker needs" , "fermenter" .)