Do mushrooms need to be cooked? Do you have to wash them?
Yes and yes! Except for a few species, it is recommended to cook and wash any mushrooms you eat, especially if they are wild.
Cooking mushrooms, as well as other foods, aids in their digestion. Chitin is one of the main constituents of fungal cell walls. It is also found in the exoskeletons of crustaceans and insects and is responsible in part for their rigidity. This characteristic, combined with the pressure exerted by a growing mushroom, is what allows certain species like the pavement mushroom to break through asphalt. Meanwhile, very few mammals produce chitinase, the enzyme responsible for breaking down chitin. Luckily, cooking for 10 to 15 minutes at 100°C is enough to break the cell walls of edible mushrooms. Adding butter, oil and salt will augment most flavors.
Just like vegetables that grow in the ground, mushrooms are naturally exposed to colorless and odorless microorganisms that can be responsible for food poisonings. Cooking will destroy these microorganisms.
Contrary to popular belief, washing mushrooms then immediately drying them before cooking is a perfectly acceptable way to remove any unwanted debris. Just be sure not to wet them before putting them into the fridge, as this will accelerate their deterioration.
Finally, some wild mushrooms like the morel contain a hemolytic toxin that attacks our red blood cells. The toxin is easily destroyed by cooking or drying. But beware! Not all mushroom toxins can be eliminated like this. For example, the deadly toxin of the destroying angel cannot be destroyed and as such, it is essential that all mushroom gatherers learn to recognize this dangerous species.