Sour or unpleasant smell
Mold on the surface or lid
Pink, green, blue, or black discoloration
Slimy, watery, or excessively thick texture
Sour, bitter, or otherwise off taste
Sour cream-like bubbling or gas in the container
Package is swollen, leaking, or damaged
Expired by a long time or stored too long after opening
Visible separation with curdled, spoiled appearance
Any sign of contamination from dirty utensils or cross-contact