Hickory nuts sound like a great choice, but we shouldn't forget about acorn oil either! The tannins in acorns are only water soluble, not fat soluble, so the pressed oil is not bitter at all even with no leaching. I've heard the red oak species produce the best tasting oils. Making your own cooking oils at home with a Piteba press (or a cheap knockoff) really shows you how much we take that stuff for granted... I use much less of it now, knowing how much raw material goes into making just a tiny bit