Long prized by leather workers for the concentrated tannins that give hides that characteristic brown finish, with proper preparation they can be a tasty and versatile wild edible.
While they can be processed into oil, starch based jellies, or a crude coffee substitute, they’re most often made into a meal or flour substitute. Acorn flour lacks sufficient gluten-like proteins to be that versatile. It was mainly used by settlers and Aboriginal people to extend their inventories of milled flour, an expensive and rare luxury of the time. Other indigenous peoples such as the Washoe Indians of California used the acorns of the Black Oak to make a simple flat-bread.
From the end of August through September, acorns of the Burr Oak are abundantly available in Winnipeg. Interestingly enough, your best best for harvesting them isn’t in the forest, but from the oaks that line may of our streets and boulevards where wildlife like deer, squirrels and birds aren’t such competition. Besides, picking them off the sidewalk and road is far easier than sifting through fallen leaves and grass.
Once harvested, acorns require a lot of handling and preparation before they can be consumed. Not only can they harbour the the oak weevil worm, they are laden with tannins. While desirable in wines, tea or coffee, acorns contain such high concentration that they are toxic to humans.
The fist step to turning an acorn into a true wild edible is to remove the fuzzy cap and tough outer shell. This can be facilitated by putting your yield into a sack or bag and smashing it against a hard surface, or stepping lightly on it.
The hats readily separate, and many of the shells will break open. Pay close attention though for small pin holes where weevils have attacked the nut and discard.
If you find a few stubborn shells, a quick tap with a hammer at either end will easily open them up. Peel the shells away and place the white meat of the nut in a container. The next step is getting rid of those nasty tannins, best accomplished by crushing the acorn hearts. A quick pulse or two in a food processor will work. If you’re feeling energetic, use a mallet.
Place acorn pieces in a clean container and fill with water. Let stand for 8-12 hours. The water will turn brown, a sign that the tannins are leeching out. Drain the water, refill the container and repeat. This can take 1-2 weeks (yes weeks) to extract sufficient tannins to make the acorns palatable.
You can also boil them off. Place acorns in a large saucepan, cover with water. Bring the water to a boil over medium heat, drain, and repeat. I’ve found that it can take 5-7 boils to purge the tannins and bring out the acorn’s earthy, nutty flavours. Don’t be deterred by the fact that the water turns brown or even black each time. You’ll never get it to run clear.
Drain well, and dry as best you can in a tea towel. Then fully dry in the sun, or, stirring often so they don’t burn, in a 200 degree oven.
When dried, pulverize the acorns into a meal using a blender, high power food processor, or coffee or spice grinder. It should resemble a course whole wheat flour.
Use your acorn meal as a partial replacement for any recipe that calls for flour. It lends itself particularly well to savory dough preparations like pizza or pot pie.
Because they it will retain a proportion of naturally occurring oil, store acorn flour in the fridge or freezer to prevent it turning rancid.