To test, fold the dried apple slice in half. It will not stick together if it is dried properly. If the apples do stick when folded, dry the apples a little longer. Another way to test is to tear the apple slice in half and look for moisture. The apple is not dry enough if you can see beads of moisture along the tear. If you like your dehydrated apples crunchy like a chip, dry them until they snap when you bend them.