Acorns the nuts that clutter your yard and our woodlands in the fall, traditionally have been used as food by the native peoples of North America. Once taken out of the shell and crushed to a smaller particle size based on the grit you want, they must be processed to remove tannin/leach out the bitterness. This can be done through immersion in multiple changes of cold water or running through cold water if held in a tight sack, pillowcase or basket or through boiling in multiple changes of water.

Thanks to http://www.practicalprimitive.com for the excellent workshop.