Against leaving very rotten bread (3)
I believe the answer is:
rye
'bread' is the definition.
(rye bread is a kind of bread)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rye that I've seen before include "Hard liquor" , "American whisky" , "Grass; whisky" , "Type of whisky" , "Cereal - liquor" .)