How to Tell When Leftovers Go Bad

To toss or not to toss: Exactly when leftovers become trash has fueled arguments of couples, roommates and co-workers since the dawn of the refrigeration. Does moldy bread go in the trash, or just get a trim around the green spot? Can Sunday's leftovers be Friday's meal? What about that day-old ground beef? While scientists have developed methods to detect spoilage -- for example, sensors that go off when milk changes consistency or a polymer to detect bacteria growth in meat -- until these...Full Story