Because cheese is by nature aged, it's tempting to play fast and loose with old or expired fromage. However, sweet, soft ricotta cheese -- actually a byproduct made from the fermented leftovers of other cheeses -- is more susceptible to mold than most types of cheese. There's more than one way to tell if your ricotta has gone bad, and the process only takes a few moments.
Smell the ricotta when you purchase it. While rotten meats are easy to identify by scent, cheeses are often naturally pungent, so it can be difficult to tell if your ricotta has gone bad by smell alone. Still, a sniff test serves as your first line of defense -- give the ricotta a whiff and compare its scent to the one you've committed to memory. Trust your gut; if the cheese makes your stomach tingle or you sense the damp tinge of mold, play it safe and ditch it. Generally, bad ricotta smells like spoiled milk.
Look for signs of mold. Observe the color of the cheese -- on ricotta, mold usually appears as a pale pink tinge or as blue or green spots. If the cheese has any signs of mold, dispose of it immediately. While mold can be safely removed from hard cheeses, its spores easily penetrate soft cheeses such as ricotta.
Check the date. As a young cheese, ricotta only has a shelf life of about two weeks from its purchase, or seven to 10 days from opening. If the cheese has an expiration date, follow it to be on the safe side. Otherwise, stick a piece of tape on the container and mark it with the date you purchased the cheese.