Sour smell that is stronger than normal
Mold growth on the surface or around the lid
Pink, green, blue, or black discoloration
Watery separation with an unusual smell
Bulging, swollen, or damaged container
Off, bitter, or rancid taste
Slimy, chunky, or curdled texture beyond normal yogurt consistency
Expired date combined with any sign of spoilage
Visible gas bubbles or fizzing when opened
Any change in appearance, smell, or texture that seems unusual