Grains for porridge (4)
I believe the answer is:
oats
'grains for porridge' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for oats that I've seen before include "Cereal for porridge" , "Wild ones are sown in youthful excess" , "Food for horses and Scots (said Dr Johnson)" , "Seed grasses" , "Food crop" .)