A Guide to Cold Leaching and Preserving Acorn Flour

  • 01 of 13

    Which Acorns Are Best for Eating?

    Large red oak acorns
    Ellen Zachos

    I'm often asked what kind of acorns I prefer to cook with, those from red oaks or those from white oaks. White oak acorns are generally considered less bitter than red oak acorns, but honestly, it makes no difference to me. I gather the biggest acorns I can find because the most labor intensive part of processing acorns is the shelling. When you can gather 50 large acorns to get the same amount of nut meat you'd get from 100 small acorns, you're ahead of the game.

    True, you may have to leach red oak acorns longer than you would white oak acorns, but leaching is so easy it's not worth worrying about. The important thing is to gather large acorns as soon as possible after they've fallen from the trees. Discard any nuts with a small hole in them. This is the exit hole chewed by the larva of the oak weevil, which has been feeding on the nut all summer. When the nuts fall to the ground in autumn, the larva chews its way out of the nut and pupates in the ground, emerging the following spring as a full grown weevil. I'll take my acorns without the side order of insect protein, please.  

    Now some of you may be thinking, "Why should I go to all this trouble, just for acorns?" I used to wonder the same thing. It sounded like a lot of work and I was afraid I'd do it wrong. True, there are a lot of steps. But each one of those steps is pretty simple. By breaking the process down into manageable pieces, I hope you'll see that it's something you can accomplish.

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  • 02 of 13

    How to Process Your Acorn Harvest

    Acorns ready to be shelled
    Ellen Zachos

    I often freeze my acorns immediately after collecting them and before shelling. Why? Because acorn season is also mushroom season and crabapple season and feral pear season and spicebush berry season, and all of these wild foods demand attention. Since acorns are the least perishable of the bunch, I freeze them until I have time to process them. 

    Freezing keeps the acorns fresh, and also kills any weevil larvae that may have come along for the ride. However, freezing also keeps the nuts moist, and acorns are easier to shell when they're dry. If you do freeze your acorns, be prepared to use a little more elbow grease to get them out of their shells. Or, dehydrate them for several hours before shelling.   

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  • 03 of 13

    Shell Your Acorns

    The Davebilt nutcracker in action
    Shelling acorns. Ellen Zachos

    The first time I shelled acorns I placed a few nuts at a time between two dish towels and cracked them with the bottom of a glass. You could also use a rubber mallet. Acorn shells aren't very thick and cracking them is easy. It's a "sitting in front of the television" activity, although it's noisy enough that you might annoy your viewing companions.

    Once I started to process acorns in greater numbers, I acquired a Davebilt nutcracker. It's solidly made and makes quick work of acorn shelling, although it takes a little arm strength. The Davebilt isn't cheap, but it's well worth the price if you're going to work with acorns on a regular basis.

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  • 04 of 13

    Choose a Leaching Method

    Shelled nuts ready to be leached
    Ellen Zachos

    Shelled acorns must be leached of their tannins before they can be eaten. While there are rumors that a sweet acorn exists, one that requires no leaching, I have yet to meet such an acorn. Unleached acorns not only taste terrible but consuming large amounts of tannins reduces the efficiency with which your intestines absorb nutrition. So let's leach our acorns.

    How you leach your acorns depends on how you want to use your nuts. Hot leaching (boiling) cooks the starch in the nuts, meaning they won't bind well as a flour. However, hot leaching is fast, and if you plan to use your acorns as snacking nuts or as a soup base, this is a good way to go.

    Cold leaching acorns results in a versatile end product, one that can be used as a fine flour or coarse polenta, as well as in all the ways you can use hot leached acorns. And when it comes to cold leaching, you have choices. 

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  • 05 of 13

    Cold Leaching Method # 1: The Toilet Tank

    Cold leaching whole acorns
    Acorns in the toilet tank. Ellen Zachos

    Step One

    Native people on several continents used to let a running stream 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. That's right, a toilet tank. Not the toilet bowl. Empty your toilet tank, scrub it, then refill the tank. Put your shelled acorns in cheesecloth or a jelly bag, and put the bag in the clean tank. Each time you flush the toilet, cold water washes through the acorns, gradually leaching them of their bitterness. How long it takes before your acorns are palatable will depend on what kind of acorns you have and how often you flush your toilet. Taste a nut every 24 hours, and when there's no bitter aftertaste, your acorns are ready!

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  • 06 of 13

    Dehydrating Whole Nuts

    These dehydrated acorns are ready for long term storage.
    Ellen Zachos

    Step Two

    After leaching, dry the acorns in a dehydrator, on the lowest possible temperature. You must keep the temperature below 150F so as not to cook the starch. If you don't have a dehydrator with a temperature setting, set it to low. If you don't have a dehydrator, you can dry your acorn meal in an oven or warming drawer, as long as the temperature is below 150F. Dehydration may take up to 24 hours, depending on your method. Higher temperatures will shorten your drying time and produce a darker flour.  

    Red oak acorns require an extra step at this point. They have a thin skin called a testa, located between the nut meat and the shell. White acorns don't. Hot leaching removes the testas, which 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.   

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  • 07 of 13

    Cold Method Leaching # 2: The Jar Method

    A hand mill for corn works well with acorns
    Grinding the acorns. Ellen Zachos

    Step One

    You can also use a second method of cold leaching, one that may appeal to people who can't get down with the whole toilet tank idea. Also, if you have a tankless toilet (like in my old NYC apartment) the jar method is the way to go. For this method, you'll need to grind your shelled acorns into a coarse meal before leaching.

    You could do this in a high-quality blender, like a Vitamix, but I prefer a hand mill, sold for grinding whole corn kernels. The hand mill lets me adjust the coarseness of the grind and also produces a uniform product. Using a blender may result in an uneven texture, as the nuts closer to the center of the canister are ground more finely than the nuts on the edges.  

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  • 08 of 13

    Soak the Acorn Meal in Several Changes of Water

    Cold water leaches the tannins from acorn meal
    Acorn meal soaking in cold water. Ellen Zachos

    Step Two

    Find a large, clear glass or plastic jar with a tight-fitting lid. Fill the jar about halfway with coarsely ground acorn meal, then top it off with tap water. Use a chopstick or the handle of a wooden spoon to eliminate any air pockets in the acorn meal, close the lid, and give the jar a good shake. Move the jar to the refrigerator. You'll notice the acorn meal settles with time, and the water takes on a dark brown color as the tannins begin to 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.   

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  • 09 of 13

    Squeeze out Excess Water

    Dried acorn meal ready for dehydration
    Use a dishtowel to squeeze the meal dry. Ellen Zachos

    Step Three

    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 possible. This may take several minutes.

    At this point, 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 longterm storage. 

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  • 10 of 13

    Dehydrate the Acorn Meal

    Dried acorn meal
    Ellen Zachos

    Step Four

    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.

    Once again, an oven or warming drawer are acceptable substitutes for a dehydrator, 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 a spice grinder also does a good job, albeit in smaller batches.   

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  • 11 of 13

    Seal & Store Your Acorn Meal

    Acorn meal, vacuum sealed
    Acorn meal ready for the freezer. Ellen Zachos

    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 storing whole nuts, meal, or flour in individual servings of one or two cups. If you don't have a vacuum sealer you can store your acorns in canning jars or in ziplock bags. Close the ziplock 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.  

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  • 12 of 13

    What Can You Make with Acorn Flour?

    Use acorn meal to make a veggieburger
    Acorn burger with tzadziki. Ellen Zachos

    Acorn flour doesn't have gluten in it, but it's a versatile flour, nonetheless. The starch you have preserved by cold leaching helps bind the flour, but it will never behave exactly the way wheat flour does.

    You can substitute acorn flour for up to half the all-purpose flour called for in most baking recipes. It adds depth and richness to this brown bread recipe and also makes tasty muffins, pancakes, and an absolutely killer sticky pudding. Use coarsely ground acorn meal as a soup base, to thicken stews, or to make burgers and falafel.  

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  • 13 of 13

    What's a Mast Year?

    A fraction of a mast year harvest
    Mother Nature is generous in a mast year. Ellen Zachos

    A mast year refers to a year when a tree produces larger than usual quantities of nuts or fruits. These bountiful years usually alternate with seasons of smaller harvests, and it's useful to be able to preserve what you gather in mast years to use when wild foods are less plentiful.

    In mast years, acorns are found in vast quantities, making it easy and fast to gather them. They also provide fats and proteins that can be difficult to find in wild edibles. Whether you're serious about including more wild foods in your diet, or just curious about the flavor of this plentiful nut, learning to cook with acorns is an excellent skill to master.

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