Gather in the fall. Those from white oak trees should not need to be
leached to remove tannins, but other kinds do. If in doubt, do it, or
they'll be bitter. Place whole, chopped, or coarsely ground nutmeats in a
cloth (a clean T-shirt will do) and tie with string. Place in boiling water
until water turns brown, then drain, and add more boiling water. Repeat
many times as needed until water is clear. In the field, just place bag
filled with nutmeats in a clear running stream until nutmeats are no longer
bitter, from 1 to several days. Spread the leached acorns in a pan and dry
in the sun or in a warm oven. Use like chopped nuts or nutmeal.
From Edible Wild Plants: A North American Field Guide by Elias & Dykeman.