The kitchen
Wild mushrooms are ruined in the kitchen far more often than in the woods.
Almost always by the same three mistakes: washing them, crowding the pan, and not cooking them long enough. Each entry gives the reason rather than the instruction, because the reason is what transfers to a species this page does not mention.
One rule outranks every technique here
Never eat a wild mushroom raw. Several otherwise excellent edibles are toxic or indigestible uncooked, morels and honey mushrooms among them, and cooking also deals with the milder irritants that make people believe they are allergic to mushrooms.
Brush, do not wash
Clean with a brush and a damp cloth, not under a tap.
A mushroom is around 90 per cent water already and behaves like a sponge. Water it absorbs at the sink has to be driven off in the pan before any browning can start, and by the time it has gone the mushroom has stewed in its own liquid and turned grey and slippery. The exceptions are morels, which need rinsing because of what lives in the pits, and cauliflower mushroom, whose folds trap conifer needles that no brush will reach.
Matters most for Chanterelle, King bolete, porcini, Hedgehog mushroom, Matsutake, pine mushroom
The dry sauté
Hot dry pan first. Fat only after the water has gone.
This is the technique that separates good wild mushrooms from disappointing ones, and it is counterintuitive enough that most people never try it. Mushrooms release a great deal of water as they heat. Add butter at the start and the mushrooms boil in a butter-and-water emulsion, absorbing fat while going soft and grey. Drive the water off first in a dry pan and the fat then fries a surface that is already dry, which is where browning and flavour come from.
Matters most for Chanterelle, Oyster mushroom, King bolete, porcini, Hen of the woods, maitake, Hedgehog mushroom
Cook it properly, and cook it through
Eight to ten minutes minimum, and longer for anything thick.
Fungal cell walls are chitin, the same material as an insect shell, and human digestion does very little with it. Heat breaks it down, releases the nutrients inside, and destroys a range of mild toxins present in species that are otherwise perfectly good: morels, honey mushrooms, blewits and chicken of the woods all belong to this group. A large proportion of people who believe they react badly to wild mushrooms have simply been served undercooked ones.
Matters most for Morel, Honey mushroom, Chicken of the woods, Wood blewit, Shiitake
Drying
The default preservation method, and for some species an improvement.
Drying concentrates flavour by removing water and, in several species, by concentrating aromatic compounds that were dilute when fresh. Dried porcini and dried black trumpets are more intense than the fresh mushroom, not a compromise for it. The soaking liquid afterwards is a strong stock and throwing it away wastes most of what you gained.
Matters most for King bolete, porcini, Black trumpet, Morel, Yellowfoot, winter chanterelle, Shiitake
Freezing, cooked
Cook first, then freeze. Never freeze raw.
Raw mushrooms are mostly water, and freezing that water bursts the cell walls. What thaws is a grey slumped mass in a puddle. Cooking first drives out much of the water and sets the structure, and the result freezes and thaws well. This is the right method for species that dry badly, chanterelles above all.
Matters most for Chanterelle, Oyster mushroom, Hedgehog mushroom, Hen of the woods, maitake
Duxelles
The way to deal with a glut, and the way to use imperfect specimens.
Finely chopped mushrooms cooked slowly with shallot until almost dry become a dense paste that keeps in the fridge for a week and in the freezer for months. It is the most efficient possible use of a large or slightly ragged haul, and unlike drying it does not care about the shape of what went in.
Matters most for Oyster mushroom, Meadow mushroom, field mushroom, Shaggy mane, lawyer's wig, Hen of the woods, maitake
Mushroom powder
Dried mushrooms ground to dust, used as a seasoning.
Powdered dried mushroom is pure glutamate and it does to a dish what anchovy or parmesan does. Black trumpet powder in particular is close to truffle at a fraction of the price, and it keeps for a year in a jar.
Matters most for Black trumpet, King bolete, porcini, Shiitake
Keep an uncooked specimen
Put one raw mushroom from every wild meal in the fridge.
This is not a cooking tip, it is standard clinical advice and it belongs in the kitchen because that is where it is forgotten. If anyone becomes ill, an uncooked specimen is what allows a hospital to identify the toxin and choose a treatment. Without one, clinicians are guessing, and the treatments for amatoxin and for muscarine poisoning are entirely different.