Sour, rotten, or ammonia-like smell
Slimy or sticky surface
Gray, green, or dull discoloration
Packaging swollen, leaking, or damaged
Meat feels tacky or unusually soft
Visible mold
Off or rancid odor after cooking
Past the use-by date and stored improperly
Left out at room temperature for more than 2 hours
Frozen pork with severe freezer burn or odd odor after thawing