How to Make Acorn Flour

Learn how to make acorn flour safely, leaching the acorns to remove excess tannins.

Acorns

Be sure to leach acorns until all the bitter tannins are removed from your acorn flour.

Photo by Brock Dolman

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The Occidental Arts & Ecology Center is a farm, community center and educational retreat that has promoted heritage foods and stewardship for decades—and in The Occidental Arts & Ecology Center Cookbook, (Chelsea Green Publishing, 2015) the OAEC Collective and Olivia Rathbone present a collection of recipes to make the best use of traditional and wild foods in the kitchen. The following excerpt is from “Main Dishes: Using Grains, Beans, Eggs, and Cheese.”

You can buy this book from the MOTHER EARTH NEWS store: The Occidental Arts & Ecology Center Cookbook.

A weekend convergence at OAEC sponsored by the Cultural Conservancy called Decolonizing Our Bodies, Nourishing Our Spirits: Native Foods Think Tank, brought together cultural leaders, scholars, activists, and chefs representing 15 US and Canadian tribes to explore the importance of the restoration of Native foods to community health. Miwok cultural representative Julia Parker demonstrated both traditional and modern acorn preparation methods that we continue to practice whenever we get the chance.

Gather acorns when you notice they are dropping, usually from September to December. Collect only large, dense acorns, passing up those that have obvious weevil holes or that are unusually light. Immediately when you get home, dump them into a large bucket of water—discard (compost or burn in your fireplace) the ones that float, keeping the ones that sink. For maximum yield, you can put them all in the freezer—this will kill any remaining weevils. If you do not have time to immediately proceed to the cracking and leaching step, dry them to prevent molding and sprouting. Spread the good acorns on a flat surface in the sun to dry, or put them on a cookie sheet and place in a very low oven for a few hours (even just the pilot light should be sufficient). Store in a basket with plenty of airflow until you’re ready to proceed. According to California Native traditions, acorns are stored with boughs of California bay leaves, a natural antimicrobial, to prevent molding.

Crack the acorns. If you don’t have a traditional grinding stone or mortar and pestle, you can improvise by cracking the acorns briskly between a heavy object and a hard surface—say, a piece of firewood or cast-iron skillet against a butcher block. Pick out the nutmeats, discarding any that are moldy.

Acorns must be leached. Eating excessive amounts of tannins contained in raw, unleached acorns can be poisonous for humans.

There are many traditional and modern options for leaching, depending upon your setup and how you wish to use them. Julia Parker explained the construction of a traditional sand filter that leaches the acorn meal in a sandbar within a clean running stream—a rarity given modern-day pollution; hence, she offered a garden hose alternative. Below is an adapted version we’ve used in the kitchen.

Grind the dry nutmeats finely by hand in a mortar and pestle or with a grain grinder. Or process in a food processor or high-powered blender with plenty of water (1 part acorn to 6 parts water, give or take) until a thin slurry forms. Strain this into some kind of permeable cloth sack—a fine cheesecloth bag, the toe of a clean pair of tights, or the sleeve of an old shirt with the end knotted off. Proceed with leaching.

Attach the cloth bag directly to the faucet of your sink and turn the water on very low. Allow the water to wash slowly over the acorn meal for several hours. In more water-scarce regions, pour cold water into a large basin and submerge the cloth sack containing the acorn meal. Massage the sack initially with your hands and let it sit. Drain and repeat every half hour (or whenever you get around to it) for many hours until the water runs completely clean. Finally, you can start tasting the mush. If there is even the slightest hint of bitterness, keep leaching until all the bitter flavor is gone. This could take as few as 4 or 5 changes (15 minutes under the faucet), as with black oak, or up to 20 or 30 changes (4 or more hours under the faucet) if using tan oak. Use the acorn mush immediately, or store it in the fridge for up to a week.

To dry the mush into flour, spread it out in a thin layer on cooking sheets and let it dry in the hot sun, in a food dehydrator, or in a low oven (200 degrees F) for a few hours, stirring once in a while for even drying. Once the flour is completely dry, break up the clumps with your fingers or run it through a coffee or grain grinder again if you want to grind the bigger chunks of acorn into a fine flour—though if you’ll be reconstituting into mush, the larger chunks are actually kind of nice. Store in an airtight container for up to 3 months.

If all else fails, you can find finely ground acorn starch in Korean markets.

More from The Occidental Arts & Ecology Center Cookbook:

Mixed Beans Recipe with Lemon Dill Butter
Easy Sauerkraut Recipe


Reprinted with permission from The Occidental Arts & Ecology Center Cookbook by The OAEC Collective with Olivia Rathbone and published by Chelsea Green Publishing, 2015. Buy this book from our store: The Occidental Arts & Ecology Center Cookbook.