At times an over abundant harvest of mushrooms leaves you with more than you can possibly consume in a reasonable time frame. There are several ways they can be preserved for future use, drying is one of them.
A relatively easy method of preserving mushrooms is by drying / dehydrating. Mushrooms should be sliced to a uniform thickness, 1/2 inch or less, before attempting to dry them. Slicing expedites the process of drying and helps ensure a uniform drying time. The thickness should also be uniform in order to ensure equal drying. There should be no moist spots as sometimes happens, particularly towards the center of the shroom. Excessive moisture will enhance the possibility of decay via bacteria and other fungus which is nurtured by the moisture.
If you have a food dehydrator, goody goody for you. Rotating the trays and turning the mushrooms periodically will help to ensure they dry uniformly. One overly moist spot is an open invitation to mold - fungus and can spoil an entire batch.
Do not attempt to dehydrate mushrooms or any produce in a microwave oven, it simply will not work. Electric dehydrators will provide a steady reliable heat, unlike microwaves which can turn your mushrooms into mush.
Temperature settings vary very little from brand to brand and amongst various dehydrator designs - generally in the range of 120 to 125 degrees F range. Other produce works at slightly higher temperatures - lower settings are best for mushrooms. On the dehydrators trays try to leave leaving an inch or slightly more between trays. Towards the end of the drying cycle, your mushrooms can easily scorch, so be sure to examine them periodically and remove any fully dried mushrooms.
Oven Drying Mushrooms
If you don't have a dehydrator - aw fiddle sticks - but alas all is not lost, you can still dry your mushrooms or other produce with a wee bit more effort. Oven Drying will work for small batches. A reliable oven thermometer is advisable and should be placed on the top tray in order to keep track of temperatures. Keep the oven door slightly ajar for some air circulation, or you can end up with mush. Rotate the racks for even drying. A slightly lower temperature than that used in food dehydrators is best 115 - 120 F.
Oven drying is not as reliable as food dehydrators primarily because the heat is not uniform. All ovens, and in particular the older gas ones with pilot lights have "hot spots" and will not produce consistent results so should be monitored constantly.
Unlike fruits and vegetables which are commonly dried to the consistency of leather, mushrooms should dried to the consistency of a thick crisp potato chip. Leathery mushrooms will readily re-hydrate and attract mold and bacteria.
Sun Drying Mushrooms
Using the sun to dry mushrooms is workable. It takes longer but is highly cost effective as it doesn't use any electric, some say the flavor and potency is more intense.
The cooperation of Mother Nature is one obstacle. Even if it doesn't rain on your parade, humid atmospheric conditions can lead to poor results.
Common sense dictates that it be done on a warm sunny day[s]. You can do it outside under perfect conditions, be sure to place a screen over your prepared mushrooms. I have at times dried tomatoes [sun dried tomatoes] on my roof. On a hot day the roof is hotter and it would work well with shrooms as well. If you're not willing or able to climb up on the roof a picnic table or what have you will suffice.
Drying using the sun indoors can also be done. A windowsill, Florida room or very well lit sun drenched location is needed. Indoors you will also want to provide suitable airflow to ward off moisture.
Lay out your sliced mushrooms on trays and place in the sunlight. Be certain not to let them come into contact with each other. It could take several days before you get the desired results, be sure to check on them at least a few times daily. If after several days your mushrooms still have a leathery consistency as opposed to the desired potato chip consistency you may want to complete the drying process in an oven at lower temperatures and shorter times than advised above under oven drying.
Storage of Dried Mushrooms
Storage should be in air tight containers. If you have a vacuum sealer go for it. If you do not have a vacuum sealer a reliable airtight container will suffice. I have successfully used Tupperware sealed in an airtight bag for added peace of mind. Mason jars will work as well if you do not plan on storing them for an extended period of time. Keep them in a dark, cool and dry location. Properly dried mushrooms have an extremely long shelf life, they can keep for years, even decades.