ichidan verb, intransitive verb
Describes food that has spoiled or gone off, often with a sour or stale smell. Commonly used for rice, leftovers, or other perishables.
暑い日に置いておいたご飯がすえてしまった。
The rice I left out on a hot day went bad.
If you don't put it in the fridge, it'll spoil quickly.