Eating spoiled food is a major cause of food-borne illness. The common culprits such as milk and meat aren't the only foods that can go bad and make you sick. Though spoilage takes longer, fungus-based foods like mushrooms can go bad, too. With a little information, you can make sure the mushrooms you're eating are fresh and wholesome.
Examine the package for an expiration date. Since mushrooms breathe after harvest, packaging that cuts down on air circulation helps retard spoilage, according to Ramaswamy Anantheswaran, Ph.D., an associate professor of food science in the College of Agricultural Sciences at Pennsylvania State University. Plastic, however, is not fool-proof. Do not buy or eat mushrooms past the printed expiration date.
Sniff the mushrooms. Mushrooms sold individually will not have printed expiration dates, and you can use your nose to make up for that. Fresh mushrooms should smell lightly of earth. A sharp, acrid or vinegary smell indicates spoilage.
Wipe the tops of the mushrooms with a paper towel. As with most other foods, water on the surface of mushrooms speeds up the spoiling process. You should get a little dirt or a tiny amount of moisture off the surface of your mushrooms. A slimy or viscous residue means the mushrooms have gone bad.
Cut the mushrooms in half with a paring knife and inspect them. Good mushrooms should have a uniform color, with the gills a few shades darker than the flesh. Green, blue or white spots indicate harmful mold or bacterial growth.