Annaquilts you use very little oil. like 3 tsp for a whole bunch of kale. I don't find them bitter but it is maybe a bit of an aquired taste? I love them. But the first bite is like .. what the heck? then they grow on you truly they do if you like veggies its just a nice variety. I think spinach is too delicate if you ask me. its thinner and a bit more watery than kale is therefore would be something you would have to watch super close not sure about the dehydrator. Surely someone has tried it before.