Pick out your mushrooms. Choose fresh mushrooms that aren't slimy, don't have soft spots or bruises. They should smell slightly earthy and not off-putting.
Wash the mushrooms. Don't soak the mushrooms in water. Simply rinse them under cool water and gently scrub the surface. Blot off any excess moisture.
Trim off the stem end and slice the mushrooms no thicker than 1/4". Keep them all the same thickness/size so they dehydrate evenly.
Place the mushrooms on your dehydrator tray or baking sheet in a single layer. It's ok if they touch slightly.
Set the dehydrator to 125º Fahrenheit (F) until the mushrooms are completely dry. If using your oven, set it to 150º F or as low as your oven will go. The timeframe can vary depending on the moisture content of the mushrooms. The mushrooms are done when they snap if you try to break them in half. Test one by allowing it to cool before breaking it in half.
Allow the dehydrated mushrooms to cool fully. If wanted, dice the mushrooms into smaller pieces or grind them into a fine powder. Store the dehydrated mushrooms in an enclosed container with a desiccant packet in a dry location.
Notes
• Use only edible mushrooms that are safe for consumption. If needed, cook the mushrooms before dehydrating to make them safe for consumption.