Becomes inedible, in a way, 4 letters
Breaks down, in a way, 4 letters
Falls apart, in a way, 4 letters
Goes bad, as a plum, 4 letters
Languishes in confinement, 4 letters
Languishes in the lockup, 4 letters
Makes the fridge stink, perhaps, 4 letters
School ___ (old iron-on patch), 4 letters
Starts to stink, say, 4 letters