While there are several ways to leach acorns, cold leaching is the best way to create a versatile end product that can be used as a fine flour or coarse polenta. Acorn flour doesn’t have gluten in it, so it won’t rise on its own. That’s why you often see recipes call for half acorn flour and half regular flour. But some baked goods, like cookies and brownies, work well with cold-leached acorn flour alone. Acorn flour adds richness and depth to anything you use it in.
Hot leaching cooks the starch in the acorns (making them suitable for soups and grits), so baked goods made with hot-leached flour may fall apart. Cold leaching preserves the starch that helps bind your baked goods, so if you like to bake, cold-leaching is the way to go.
You have choices when it comes to cold-leaching acorns. Here are three methods, all of which work well. The main difference is how much time it takes to get the job done.
The Lazy Way to Cold Water Leach Acorns
Native peoples used to let running water do the work of leaching by tethering baskets of acorns in a stream and allowing the cold water to run through the nuts for several days. I don’t have a stream, but I do have a toilet tank.
The easiest way to cold leach acorns is to stash them in the back of your toilet. To be clear: I’m talking about the toilet tank, not the toilet bowl. Empty the toilet tank, scrub it, then refill it with clean water. Put your shelled acorns in a fine mesh bag and place the bag into the toilet tank. Each flush runs cold water through the nut meats, leaching them of their bitterness. Taste test at intervals after 24 hours. You may need as long as two to three days, depending on how often you flush.
For long term storage, dry your leached acorns in a dehydrator on the lowest possible temperature. You must keep the temperature below 150F to avoid cooking the starch. If you don’t have a dehydrator with a temperature setting, set it to low. If you don’t have a dehydrator at all, you can dry your acorn meal in an oven or warming drawer, as long as the temperature is below 150F. The nuts are fully dried when they are brittle and can be broken in half with a snap.
Red oak acorns require an extra step at this point. All acorns have a thin, papery skin called a testa, located between the nut meat and the shell. The testas of white acorns adhere to the shells, but the testas of red acorns stick to the nuts. Hot leaching removes the testas, which may have a bitter taste. If you cold leach, you’ll need to rub off the testas before you cook with your acorns. Fortunately, after drying, the testas fall away with a gentle rubbing.
Dehydrated, leached acorns can be ground into flour right away, or stored whole. In any case they should be sealed and stored in the freezer. Acorns are high in fat, which may turn rancid if stored at room temperature.
The Jar Method for Cold Leaching Acorns (still pretty easy for a lazy forager)
If the idea of using the toilet makes you uncomfortable, try the jar method. It’s low tech, and requires only a little more effort on your part. For this method, you’ll need to grind your shelled acorns into a coarse meal before leaching. You can do this in a high quality blender, like a Vitamix, or with a hand mill, sold for grinding whole corn kernels. A hand mill produces a coarse grind, which is perfect for recipes like falafel and veggie burgers, while the Vitamix produces a finer flour, excellent for baking.
Find a large, clear glass or plastic jar with a tight-fitting lid. Fill the jar halfway with coarsely ground acorn meal, then top it off with tap water. Use a chopstick or the handle of a wooden spoon to poke out any air pockets in the acorn meal, close the lid, and give the jar a good shake. Move the jar to the refrigerator. The acorn meal will settle out of the water with time, and the water turns brown as the tannins leach from the nuts.
Let the jar sit for 24 hours in the refrigerator, then carefully pour the water off the meal. Don’t worry about getting every last drop. Refill the jar with water, and replace the jar in the refrigerator. You’ll need to do this several times, depending on how bitter the nuts were to begin with. After pouring off the water for the third time, taste the acorn meal. If it’s bitter, continue to change the water every 24 hours until no trace of bitterness remains.
Once the bitterness has been leached from the acorn meal, pour the meal out into the center of a dish towel. Gather the four corners of the towel together and twist the dish towel closed, then continue to twist until water begins to drip from the bottom of the dish towel. When no more water can be removed by twisting, squeeze the dish towel as hard as possible to remove as much water as you can.
You can dry and freeze the acorn meal, or freeze the wet acorn meal. If you do the latter, you’ll need to adjust the liquid in any recipe you use it in.
The Fastest Way to Cold Leach Acorns
If you’re in a big hurry for leached acorn flour, try the running water method. This is the most labor-intensive method, but is by no means difficult. Put a cup of shelled nuts in a blender and add water to four to five inches above the level of the nuts. Pulverize to create a slurry, and set aside. (If you have already ground your acorns into meal, but not yet leached them, you can also use the method described below.)
Place a large colander in the sink and line it with a dishtowel. Pour the slurry or meal into the colander, then run cool water into the colander and stir with a large spoon. After eight minutes of stirring, taste the slurry. If there is any bitter flavor, let the water run for another two or three minutes and taste again. You should be able to stir without spilling, which is why this is best done in small batches in a large colander. Once the acorn meal is not at all bitter, squeeze out as much excess water as possible, as described in the jar method, above.
You can freeze the moist acorn meal as is, but you’ll need to use slightly less liquid in any recipe you make with the flour. I prefer to fully dry the flour before sealing it for long term storage.
If you have a dehydrator with fruit leather sheets, spread the moist acorn meal across the sheets and set the temperature to the lowest possible setting. Depending on the humidity where you live, your meal will take between 12 and 24 hours to dry. Check it after several hours and break up any large clumps to speed the drying process. An oven or warming drawer will also work, as long as the temperature is below 150F.
You can stop here, at the dried acorn meal stage, or grind it to make a fine flour for baking. The dry grains canister of a Vitamix does a great job in under a minute, but an ordinary spice grinder also does a very good job, albeit in smaller batches. I like to keep jars of both coarse meal and fine flour on hand.
Once the acorns (whole or ground) have dried, they’re ready to be measured, sealed, and stored. A vacuum sealer is a handy tool for preserving freshness, but if you don’t have a vacuum sealer you can store your leached acorns in ziplock bags. Close the bags most of the way, then suck out as much air as you can with a drinking straw before sealing them all the way.
Whole nuts will keep for several years in the freezer; the smaller amount of exposed surface area means slower oxidation. Flour and meal should be used within a year.
This article was originally published in Backwoods Home magazine. (Nov/Dec 2016)
Note: I’ve written about the gelatin method for cold leaching acorns, but I’m not convinced it’s worth the work. I’d love to hear from anyone who’s tried it.