Mushrooms that have gone bad are a sticky and slimy, and will be darker in color. Once mushrooms begin to develop a slight slime, they can be cooked to extend the shelf life for several more days.
Fresh whole mushrooms usually last around seven to 10 days. Sliced fresh mushrooms will last around five to seven days. When mushrooms are cooked, they can last anywhere from seven to 10 days. The best way to store mushrooms to extend their shelf life is to leave them whole in a sealed plastic bag in the refrigerator. If mushrooms are beginning to turn bad, they can be browned in oil with garlic and then be placed in a sealed container in the refrigerator until ready to eat.