First, clean the mushrooms. It is best to get all of the dirt off with a brush.
Go ahead and wash them in water, scrubbing with a vegetable or mushroom brush as necessary. This will make your prep much easier.
Depending on what seems easiest for the shape of the mushrooms, either clean them whole and then slice them, or vice versa.
Slice the mushrooms between 1/4 to 1/2-inch thick. The thicker the slices, the longer they will take to dry.
Arrange the cleaned, sliced mushrooms on the dehydrator trays, making sure that none of the pieces touch or overlap.
Dry them at 110F/43C until the pieces are crispy dry. This will take 4 to 6 hours for 1/4-inch slices, up to 8 hours for thicker slices.
Allow the dried mushrooms to cool completely before transferring them to glass jars. Cover tightly with lids and store away from direct light or heat.
To use dehydrated mushrooms, pour boiling water over them in a heat-proof bowl. Let them soak for 20 to 30 minutes. Drain, reserving the richly flavored soaking liquid for soup stocks and sauces. Use the rehydrated mushrooms as you.
*This information provided by About Food. For more information please visit foodpreservation.about.com