Pumpernickel flour (3)
I believe the answer is:
rye
'pumpernickel flour' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rye that I've seen before include "New York bread" , "Cereal grass - Sussex Cinque Port" , "Hardy cereal crop" , "One of Cinque Ports" , "Grain used in flour and whiskey" .)