Safely eat acorns by first soaking them in warm water for a few hours before eating them. Soaking acorns removes tannic acid, which can cause nausea and digestive issues. Once most of the tannic acid has been leached away, roast the acorns, or dry them and ground them into flour. The resulting flour can be used to make a variety of foods.
To safely cook acorns, begin by smashing the acorns with a heavy object. Remove the shells, and discard them. Then soak the nutmeats in a warm water bath for several hours, tasting periodically to see if the acorns are still bitter. If warm water is not available, leach the acorns using running water (such as a stream). Leaching acorns with running water takes significantly longer. Place the acorns in a vessel that allows water to flow through, such as a woven basket, and keep the vessel in running water for several days.
Once the acorns have been leached of tannic acid, roast them with salt on a baking sheet. Alternately, acorns can be dried and ground into acorn meal, then further ground into acorn flour that can be used to make bread or other baked goods, including cookies.