Apparently all acorns are edible:
“‘Sweetest’ Acorns, meaning lowest in tannin: East Coast White oak, the Emory oak of the Southwest, the Pin oak of the South, the Valley and Blue oaks of California, the Burr oak of the Midwest, as well as the Cork oak and the well-named Bellota oak of Europe.
All acorns should be leached with water to remove bitter tannins, which will a) make your mouth feel and taste like felt, b) make you a bit nauseous, and possibly c) constipate you for days.
Getting those tannins out is the big barrier to cooking with acorns. But it ain’t no biggie. With my Valley oak acorns, after shelling I drop the acorn meats directly into my stockpot that was two-thirds full of water. When I fill the pot about a third of the way up with shelled acorns, if I am in a hurry, I bring the pot of water to a boil. The water turns dark. As soon as it boils, pour the water off into the sink and repeat the process. It requires about five changes of water to get Valley oak acorns to taste like chestnuts.” http://honest-food.net/2014/10/13/how-to-eat-acorns/
Photo: Cork Oak.