Turn stale
Else clues• Become inedible
• Become spoiled
• Curdle
• Curdle, as milk
• Deteriorate
• Putrefy
• Rot
• Sour
• Sour, perhaps
• Spoil
• Spoil, as milk
• Sprout mold, say
• Stink up the fridge
• Turn
• Turn in the fridge
• Turn sour
• Turn sour, say
• Turn to the dark side
• Turn, as food
• Turn, in a kitchen
• Turn, in a way