You can dehydrate and rehydrate potatoes to extend the shelf life for years. The starchy potato keeps very well in the pantry once all its moisture has been removed. Dried potato slices are tough and nearly inedible until they are fully rehydrated. Hard dehydrated potatoes become moist and soft when they are soaked in a warm liquid bath for a few minutes. Save money by dry-preserving fresh potatoes that would otherwise be headed for the trash.
Wash the skins of the potatoes with a nylon-bristled scrub brush under cold running water.
Set a mandoline slicer to its thinnest setting. Pour water and citric acid or lemon juice into a large mixing bowl.
Slice the clean potatoes directly into the bowl of acidic water. Quickly move sliced potatoes into the water if you are not able to rest the mandoline on the rim of the bowl.
Lay out double layers of clean and dry lint-free kitchen towels on a flat surface. Spread the potato slices in a single layer on the towels. Pat dry the upward facing portion of the slices with another clean towel.
Move the potato slices to the perforated racks or screens of a food dehydrator. Follow the manufacturer's instructions on the dehydrator. Dry the potatoes at medium-low heat for 8 to 12 hours or until they are crisp.
Grease the interior surfaces of a casserole dish liberally with margarine or butter. Distribute dehydrated potato slices evenly in the casserole until they just barely rise above the rim of the dish.
Pour equal parts milk and water into the casserole until about half of the dehydrated potatoes are submerged in liquid. Add savory seasonings like salt, pepper and herbs to increase the flavor complexity of the dish.
Cover the casserole dish in a sheet of aluminum foil. Crimp the aluminum foil around the rim of the dish to create a moisture-tight seal.
Slide the covered dish into a preheated 350 degree F oven for a 40-minute bake. Lift the foil carefully to vent steam away from your face and hands. Poke the potatoes with a fork to see if they are soft and fall apart or if they need more baking time with the cover on.
Remove the aluminum foil once the potatoes are rehydrated and soft. Cover the potatoes with shredded cheese if you want to add a cheesy crust to the potato dish. Bake the potatoes without the foil for another 10 minutes at 375 degrees F to brown the top layer and intensify the flavors.