Most mushrooms dry well. We recommend using a food dehydrator (follow manufacturer's instructions), or drying them in a barely warm (135 to 150 degrees Fahrenheit) oven. Slicing them into uniformly thin pieces can speed up the process. If you're using an oven, evenly space the mushrooms on ungreased cookie sheets. Turn them occasionally. You can also lay them outside on a screen, or string them so they can hang in the sun.
To prevent decay, dry them until they are cracker hard (snap when you try to bend them) and are not bendable.
You can keep dried mushrooms in an airtight container, in a cool, dark place, for a very long time.
To use, rehydrate them in a bowl of warm water for 30 to 60 minutes. Keep the delicious mushroom-infused water for a soup, sauce, or another dish.
Some mushrooms, like chanterelles, may become a bit rubbery after they are dried. If this happens, you can grind them into a powder in a spice mill or coffee grinder and use it as a seasoning.
Sauté and Freeze Method
After cleaning, sauté them in a little butter, salt, and pepper — add onion, garlic, or shallot for even more flavor — until the water in the mushrooms has evaporated.
Let the mushrooms cool, then spoon them into quart-sized freezer zip bags (pushing out all the air) and place in the freezer. Try freezing the bags flat on a cookie sheet; they store well in the freezer that way and will later thaw out quickly.
Your frozen pre-sautéed mushrooms will taste great in sauces, soups, casseroles, egg dishes, stir-fries, curries, and pilafs.
Some people pickle mushrooms. Many recipes and techniques are online, but be aware: the delicate mushroom flavors may be overwhelmed by the pickling solution.