Rinse harvested peppermint leaves with cold water while they are still on the stem. Blot the leaves dry with paper towels.
Pluck fresh peppermint leaves from the stems and arrange in a single layer on the perforated tray of your food dehydrator.
Place the cover over the dehydrator and rotate to lock it in place.
Set the food dehydrator to 100 degrees Fahrenheit and start the appliance to begin drying the leaves. Maintain this temperature, since flavor and vitamins are lost when herbs are dried at higher temperatures.
Test the leaves with a fingertip every two hours until they are crisp.
Store whole or crushed peppermint leaves in airtight glass containers.