A while back I wrote three post on cooking with acorns. Cooking with Acorns is easy, Uses of Acorns and Acorns. These articles show you how to cook with acorns and some of their other uses. Besides being edible, the tannic acid you wash out of the acorns is useful.
Tannic water is antiviral and antiseptic. It can be used as a wash for skin rashes, skin irritations, burns, cuts, abrasions and poison ivy or poison oak. If you have a sore throat you can even gargle with tannic water or use it as a mild tea for diarrhea and dysentery. Externally dark tannic water can be used on hemorrhoids. Hides soaked in tannic water make better leather clothing. Using the brown water turned hides tan colore and that is why it is called tanning.
Acorns from different species of trees will taste different. Some will be almost sweet with very little tannic acid, while others are extremely bitter. They range from the Emory oak of the southwestern United States and northern Mexico, which is so mild it can be used without processing, to some black oaks which are very bitter requiring a lot of leeching to be edible.
The best acorns to harvest are those of the white oaks, such as the swamp oak, Oregon white oak, and burr oak, as they contain less bitter tannin. Some of the white oaks around where I live are barely bitter and some of our family dogs eat them all the time. Luckily, nearly all acorns can be made usable with natural processing which renders them nutty and sweet.
I have always thought that these uses were about the limit of usefulness of the acorn. That is until I read the following article. Acorn Grubs: Bait, Trailside Nibble. For years I have been throwing the acorns with grubs away. Now I find I should have been eating them.
As you can see from the article, they are the most common insect found in acorns and I have been throwing them away. From now on, I will be eating the grubs with my acorns, another good source of fat and protein.