As with any perishable food, consuming mushrooms that have passed their expiration date is dangerous and can make you very sick. Fresh mushrooms are tasty and nutrient-rich when they are firm and dry. Sliminess is one indicator that a mushroom has gone bad -- and that you should avoid cooking with it.
When mushrooms become slimy, it is a sign that they have begun to spoil. According to the University of Buffalo, the three microorganisms that cause food spoilage are molds, bacteria and yeasts. A rotting mushroom can have a combination of the three growing on its surface. Though all mushrooms eventually decompose, certain factors -- such as improper storage and proximity to spoiled food -- can cause mushrooms to spoil sooner.
How To Tell
Slimy mushrooms often display other characteristics of spoilage that can help you decide whether or not to toss them. Spoiled mushrooms usually have a foul or ammonia-like odor, so be sure to smell them before consuming. Color changes are also common; white button mushrooms, for example, will turn dark brown or black when they are spoiled. If you have any doubts, test the mushroom by smelling, touching and observing it for these signs, and be sure to wash your hands thoroughly with soap and water when you are finished.
Consuming spoiled, slimy mushrooms raises some major health risks, such as food poisoning. Symptoms of food poisoning usually appear within one to three days, according to the Wisconsin Nutrition Education Program. These include upset stomach, diarrhea, cramping and vomiting. Food poisoning is particularly dangerous for those with compromised immune systems, such as infants, pregnant women and the elderly.
Proper storage is essential for ensuring a normal shelf life for mushrooms. Properly stored fresh whole mushrooms will last seven to 10 days. The Ohio Agricultural Research and Development Center recommends storing mushrooms in the refrigerator in a sealed container that is as moisture-free as possible. Avoid storing mushrooms in the produce drawer, which tends to have a higher humidity level than the rest of the refrigerator. As a general rule, it is better to consume mushrooms as close to the purchase date as possible to ensure optimal freshness.
Clean mushrooms by gently wiping them down with a soft brush or damp cloth. You can also rinse them and pat them down with a paper towel. Cleaning a mushroom that has gone slimy will not render it safe to eat. Once you identify any signs of spoilage, discard the mushrooms.