Sour smell that is stronger, unpleasant, or different from the normal tangy yogurt smell
Mold on the surface or around the lid, including green, blue, black, or pink spots
Visible separation with liquid that looks unusual, especially if the yogurt is also clumpy or discolored
Off taste that is bitter, overly sour, or otherwise not normal
Change in color, such as yellowing, graying, or any unusual discoloration
Puffy, bulging, or damaged container lid
Slimy, fuzzy, or watery texture that seems abnormal
Signs of gas or bubbling when opened
Past the expiration or use-by date, especially if stored improperly
Left unrefrigerated for too long
Packaging that is leaking, cracked, or compromised