I found this extract below on the internet. I also believe that in parts of Germany and Poland during the last war in desperation they drank a kind of ersatz coffee made from ground acorns, which was apparently pretty dreadful so they must have been desperate.
" Many people have heard that acorns can be eaten, and a few have actually put them in their mouths, only to spit them out while their faces puckered up. This is due to the tannic acid in the acorns, which much be leached out. To do this, bring a large pot of water to a boil, then dump in the shelled acorns. Let them boil until the water turns a dark color, then remove the acorns and put them into another pot of clean, boiling water. Continue this process until they no longer have the puckering effect when you chew on them. Then use them for snacks, grind into flour, or use any way you please. It is important to put them into boiling water for good-tasting acorns, as putting them into a pot of cold water, then bringing it to a boil tends to lock in the tannic acid. Don't throw out the water, as it is naturally astringent (contracts or tightens up tissues) and great for the skin. By now you might be curious how this relates to poison ivy. The connection is that acorn water is amazingly effective in eliminating it. A recent discussion with a quick-witted summer camp director from Pennsylvania confirmed my anecdotal evidence. I was informed that it had eliminated symptoms in 95% of cases at his camp within three days. The method used in this case was to pour the acorn water into ice trays and freeze, then rub the ice on the affected area. Cold also helps with inflamed tissues, making the ice an ideal delivery mechanism. If you grind the acorns into flour you can make delicious and nutritious acorn bread."
I'll leave you to test it out and report back !!!