Fill a large bowl with cool water. Add either Ball Fruit Fresh (see container for measurements) or 1 tsp. of lemon juice per cup of water. This will prevent the apples from browning while you process them.

Wash the apples and remove any blemished spots. If preferred, peel the apples. However, peeling is not required for freeze drying.

Core and slice the apples. You can save a lot of time and effort with a corer and slicer. But if you don't have one, a knife will do the trick. Just try to keep the slices uniformed in size.

Drain the apples, and place them on the freeze dryer trays. To reduce dry time, you can pat the apples dry, but this isn't necessary. The apples can overlap, but try to leave space between each slice if possible. Overlapping will increase the dry time (as you can see in the photo, I don't worry too much about overlapping).

Place the trays into the freeze dryer. Close and seal the freeze dryer door. Make sure the drain valve is close (it should be perpendicular to the drain line). Hit start.

Let the freeze dryer do its thing. How long the process will take depends on the number of apples, the size of the slices, and the temperature of the room (if your freeze dryer is in a garage like mine, for example, it can take longer on hot days). But it usually takes around 12 hours or more.

Once the freeze dryer has completed the process, check the apples to make sure they are completely dry. If there is any moisture at all, return all of the trays into the machine, and select "more dry time."

When the apples are completely dry, store them in a glass jar with an air-tight lid (short-term storage) or in mylar bags with an appropriately sized oxygen absorber (long-term storage up to 20+ years).