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.

Rotting Butter on a Plate in a Fridge

(Jonathan Kitchen/Digital Vision/Getty Images)

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 are available on a mass scale, food science and safety experts have some tips.

Deadly and Invisible

First tip: slimy, stinky, spotty or chunky changes in food don't mean very much in terms of safety.

"It may not taste good, that doesn't mean it's going to make you sick," said Michael Doyle, director of the Center for Food Safety at the University of Georgia in Griffin.

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