Fresh mushrooms can be classified among foods that seem completely fine in the refrigerator one day and questionably edible the next. If the mushrooms you're saving have sat so long that they're starting to look or feel like slimy slugs, then it's probably time to throw them out.
Buying Fresh Mushrooms
The key to shopping for 'shrooms is to pick those that are in the best shape, which means they'll also last the longest in the refrigerator. Look for mushrooms with somewhat uniform color rather than dark blotchy spots dotting the caps or stems. Those that have blotchy wet spots on them are on their way to becoming rotten mushrooms.
Buying loose mushrooms offers the opportunity to inspect each one individually. Check each one for how it looks, feels and smells. A good mushroom smells earthy – a bit like dirt – and never fishy or sour.
If packaged mushrooms are your only option, visually check the fungi through the plastic wrap, avoiding packages that look wet inside or that contain any decaying, mushy mushrooms. Packaged mushrooms rarely have a use-by date on them, so visual inspection is a must.
Fresh Mushroom Shelf Life
Fresh mushrooms stored properly in the refrigerator should last at least three days but often more than a week. Whole mushrooms keep better than the sliced variety. The sliced ones tend to discolor and decompose faster since the inner parts of the mushrooms are exposed to air.
If you've purchased loose mushrooms, keep them in a zippered plastic bag in the fridge, leaving the bag's seal partially open. This helps gases escape from the bag, which prolongs the shelf life of the mushrooms. Do not wash the mushrooms before storing them, as exposure to water could make them go bad quicker since some mushroom varieties tend to absorb moisture.
If you are cooking with packaged mushrooms, and you don't use the entire package at once, reseal the container as best as possible with the plastic wrap originally on the package. Otherwise, cover the package with fresh plastic wrap, poking a few tiny holes in the top to allow air to escape.
To Use or Refuse
If you bought a package of mushrooms last week and wonder if the fungi are still fresh, check them thoroughly once again. Sometimes, a few of the mushrooms may look bad or feel slimy while the rest seem fine. Separate the slimy or stinky ones from the rest, throwing those rotten mushrooms out. Then, carefully inspect those in the good pile.
A slight amount of slime or a wet feel on one or two mushrooms might not cause harm if they're cooked right after cleaning them, but it's best to avoid them because they could cause food poisoning or at the very least, nausea. Rinsing the mushrooms that are in between good and bad as well as the good ones gives you the chance to check them all thoroughly.
Even good, fresh mushrooms will feel a bit slimy when they're wet from rinsing. Pat them dry with paper towels and then inspect and sniff them again. Discard anything that just doesn't seem like it should be eaten.
Eating Bad Mushrooms
Eating bad mushrooms could mean the mushrooms were actually of a potentially toxic, wild variety or that the mushrooms were once safe but were eaten long after their prime. Wild mushrooms should not be eaten unless they're gathered by an expert who can tell the difference between species. Sometimes, toxic varieties look nearly the same as edible types.
Any mushroom, whether wild or store bought, is best eaten cooked, as many types contain a carcinogen that cooks off when heating. However, cooking a poisonous mushroom variety will not remove the toxins, so it's still incredibly dangerous, and they should never be eaten.
Store-bought mushroom poisoning is highly unlikely, although eating a bad or spoiled mushroom could cause illness or an upset stomach. If they are left out for hours after cooking before placing them in the refrigerator, for instance, they could cause tummy troubles once reheated.