Sour or off smell
Lumpy, curdled, or separated texture that does not mix back together
Strange or bitter taste
Mold in the carton, cap, or on the surface
Bulging, leaking, or damaged packaging
Expired use-by or best-by date
Popped seal or broken seal before opening
Foamy, fizzy, or gas-producing appearance
Color change to yellow, gray, or unusually dark
Thick slime or stringy texture
Left unrefrigerated too long after opening
Tastes fine at first but leaves an unpleasant aftertaste
Visible chunks or particles that are not normal
Carton smells bad when opened
Signs of spoilage after freezing and thawing