Toss milk when it starts smelling sour, usually a week or so after opening. Cut away mold from hard cheeses like parmesan, but it permeates soft cheeses like ricotta and goat, so chuck 'em.
Meat and poultry
Discolored? Slimy? Smelly? Get rid of it.
Cuts of steak: What to look for
Dried-out is fine, but don't put anything with mold or a slimy residue in your mouth.
Most have a shelf life of two years, but if it smells sour or funky once opened, toss it.
Most last up to six months unopened. If you find weevils, it's time to restock.