Sour smell that is unusually strong, rotten, or unpleasant
Mold growth, discoloration, or spots on the surface or inside the container
Chunky, slimy, or stringy texture beyond normal separation
Bitter, rancid, or off taste
Package is bloated, leaking, or damaged
Expired date has passed by a long time
Fizzing, bubbling, or unusual gas release when opened
Separation that does not mix back together after shaking
Visible curdling that looks abnormal for buttermilk
Stored improperly or left out at room temperature for too long