Pretreating is really only necessary for color preservation in most cases. If you don't care about brown bananas or apples (which you can cover with a cinnamon sprinkle), then no, it's not necessary. However, for breaking skins on skinned berries, a simmer until the skin breaks is a great way to prep them for efficient dehydrating (though you can accomplish the same thing with a knife or skewer as I do for u003ca href=u0022https://www.thepurposefulpantry.com/how-to-make-blueberry-powder/u0022u003edehydrating blueberries.u003c/au003e)