Food dehydrators perform the same function as drying fruits or vegetables in the oven, or, more traditionally, in the sun. Dehydrators remove moisture from plums through the combined effects of warm temperatures—never greater than 140 degrees—air circulation and low humidity. The longer you dry fruit, the more brittle it becomes. For this reason, pay close attention to fruit toward the end of its drying cycle.
Wash plums in hot water, cut them in half and remove the pits.
Spray the drying trays with nonstick cooking spray to keep the plums from sticking during the drying process.
Place the plums in a single layer on the drying trays. Do not allow pieces to touch or overlap each other.
Dry your plums until their moisture content is about 20 percent--usually 24 to 36 hours. You will know they have reached this point when a cool piece of dried fruit can be folded in half without sticking, when it can be squeezed without any moisture leaking out and when there is no visible moisture on the dried fruit.
Allow the dried plums to cool for 30 to 60 minutes before packaging or conditioning.
Put the dried plums loosely in glass or plastic jars and seal them for 7 to 10 days. Shake up the pieces once a day. If you observe any condensation, the fruit needs more time in the dehydrator. This is known as "conditioning." It redistributes excess moisture in some plum pieces to other pieces with less moisture.
Package the fruit in resealable containers or bags after they have dried completely. Do not wait too long to package your plums; moisture can begin to reenter them if they sit out too long.