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Cold Leaching Acorns: Three Ways

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. Acorn flour doesn’t have gluten in it, but it’s a versatile flour, nonetheless, especially when the tannins are leached with cold water.

Because it contains no gluten, acorn flour won’t rise on its own. That’s why you’ll often see recipes calling for half acorn flour and half regular flour. However, 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. The starch you preserve by cold leaching helps bind the baked goods and lets you use your acorn flour in lots of different ways.

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.

cold leaching acorns

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.

acorn testas

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.

cold leaching acorns

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.

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.

strained acorn meal

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.

drying acorn flour

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.

vacuum sealed acorn flour

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.

Ready to bake? Try this Steamed Acorn Brown Bread or these Acorn Lace Cookies.

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.

cold leaching acorns

36 comments

  1. That said, even sweet acorns should be leached to remove what tannins exist in them because several studies show that unleached acorns can make you constipated and can harm your teeth.

  2. awefilms.com says:

    This is a good way to leach acorns without using fuel for boiling water, and you do not denature a particular starch in the acorns that acts a little like the gluten in flour, i.e.

  3. Andrea says:

    I’m doing the cold leaching in a jar method. For the first few water changes, the water was dark but clear. After that, the water stayed cloudy.. What’s up with that? I used a Vitamix to make the acorns very fine.
    Thanks!

    • Ellen says:

      Don’t worry about the cloudiness, Andrea, those are probably the acorn starch particles in suspension. A small amount of starch is released when you grind the acorns. Some people separate the starch from the flour and use it to make puddings and pie filling, but you need a very fine filter for that, like the kind used to filter maple syrup. I keep the all the solids together. Since acorn flour doesn’t contain gluten, it doesn’t stick together like wheat flour, but the starch gives it some binding ability. Have you tasted the flour? How’s the flavor coming along?

    • Ellen says:

      Andrea asked the following question about toilet tank cold leaching: “Do you chop the acorns into pieces for tank leaching or leave them more or less as they come out of the shell?”

      When I cold-water leach in the toilet tank, I leach large pieces. Sometimes they’re whole, sometimes they’re halves or quarters. However they come out of their shells is how I leach them and how I dry them. I don’t grind them until I need to use them, and then I’ll grind either fine (for flour), medium (for grits), or large (for nuts).

      When I cold leach in a jar, I grind the nuts fine prior to leaching.

      • Andrea says:

        Thanks, Ellen! How many days do you usually leave your acorns in the tank? I know it depends to some extent on how often one flushes, but I was wondering what you typically experience.

        • Ellen says:

          It also depends on what kind of acorns you’re leaching. Red oak acorns generally contain more tannins than white oak acorns, and take longer to leach. Typically, with two people in the house, it usually takes me 4-7 days to leach white oak acorns. But really, the only way to know when your acorns are done is to taste them.

  4. C4t says:

    I just put the shelled nutmeats in a mesh bag and let it soak in a big tub of water on the back porch. Every morning I pour it out and fill up from the hose until the water’s no longer yellow brown.

    Guess I’m doing it wrong…

    • Ellen says:

      Nothing wrong with that! Sounds like an excellent method. It’s been too cold here recently, but for people who live where the water wouldn’t freeze, it’s a great idea.

      • Pam says:

        Wondering what the health risks of stream leaching are…I wouldn’t drink water from the stream without treating it so would I be ok leaching acorns?

        • Ellen says:

          I’ve never done it, but I THINK it would be fine, because: 1) After leaching acorns I dry the nuts to preserve them, which removes the water from the nuts. 2) Stream leaching is cold leaching, so I’m guessing you’d be using the acorns for flour. In which case you’d be baking the acorns and the high temperatures would kill whatever organism you’re concerned about. If you’re worried about chemical pollution, I’m sorry, but I don’t know enough to address that.

          • Andrea Deyrup says:

            I agree with Ellen that the microbial risks (e.g., Giardia) will be abated by drying and cooking; however, the pharmaceutical/toxic risks remain. Medications (e.g., endocrine disruptors) and toxins such as arsenic, mercury and lead can be in the water, depending on your location. I wouldn’t do it. I did try the toilet tank method, but we’re on well water so it’s not chlorinated and I got some algae growth (which isn’t a big deal, but I opted for just doing a couple jars in the refrigerator). Toilet tank would probably be safer than a stream.

          • Ellen says:

            Thank you Andrea, you said it better than I did. Pharmaceutical/toxic is what I meant by chemical. I started out with the toilet tank method when we lived in PA and were on well water. I never had any algae growth, but I, too, now use the refrigerator jar method. If I’m in a hurry, I do the pour through/stir method.

  5. Keith says:

    Well informed article and conversations on acorn nut leeching. I’ve always wanted to know how to utilize the acorn as a food source having grown up in an oak tree rich environment and thinking what do the squirrels know about the acorn that I don’t.

  6. Liam says:

    Great article, however I am confounded to get the testa off the nutmeat. Will leaching reduce the bitterness of those as well? I have been cold leaching mine for 10 days now, and they are still very bitter. Thanks in advance

    • Ellen says:

      Hi Liam, Don’t be discouraged! You may have found acorns with a high level of tannins, but you can still get rid of them, it just may take a little longer. I’m guessing you’re trying the toilet tank method, is that right? Have you noticed any decrease at all in the bitterness after ten days? How often are you flushing your toilet? The testas will some off easily once you dry the acorns. It’s much harder to remove them when the nuts are wet. Do you have a dehydrator?

  7. Brian Maloney says:

    I have some questions. I’ve been cold leaching some acorn nut meats in some glass jars for about 9 days (I started leaching them Sunday evening, November 10, 2019). My first question is this. Should I have the lids off? The lids have been on all that time, but water’s starting to smell odd.

    My second question is this. Can I wash mold off the dry acorn nut meats that haven’t been leached? They were sitting in an open container, waiting to be leached. There’s still barely any mold, but I hope I can clean those acorn nut meats rather than throw them out.

    • Ellen says:

      Hi Brian, I’m happy to help, but I need a more info. Are the cold-leaching acorns whole or ground? Have you been changing the water, and if so, how often? As for your second question, I guess the acorns weren’t thoroughly dried before you put them in the jar. I’d like to see a photo of the moldiest acorn. Hopefully you can wash off all the mold, then dry the nuts thoroughly before storing, but I’d like to see how much mold there is before I say for sure. You can post the photo on my FB page: https://www.facebook.com/thebackyardforager/.

  8. Brian Maloney says:

    Hi, Ellen. Most of the acorns that have been leaching are in pieces because only a small percentage of them stayed whole when they were pried out of their shells.

    At first, I was changing the water 2 or 3 times a day (that was for most of the 9 days). On the seventh day, the acorn nut meats went a whole day without the water getting changed, and yesterday (Monday, November 18th), I only changed the water once. I started changing the water less frequently because it started taking a lot longer to get colored by the tannic acid.

    Two other possibly important facts are the following. First, I left the skins on the all the acorn nut meats ’cause it was too difficult to remove them when they were dry. I plan(ed) on removing them after draining the nut meats and dehydrating them in the oven at <150⁰F. Secondly, the slightly moldy acorn nut meats were put in an open, plastic container. That container has several times the nut meats' collective volume of air between them and a screened lid that was air drying on top of the opening to the container (I use that screened lid when draining the water from the glass jars of the "leach water").

    I don't know how to attach photos to posts on this blog, so I'll just e-mail them to you.

  9. Karen says:

    Hi Ellen, I just found your page after doing a trial run on processing some red acorns. I’ve only done 2 cups as this is my first attempt. I didn’t know anything about removing the testas. I did a coarse grind with a nut grinder (including the testas) and proceeded to leach in a quart jar, shaking, draining, etc., several times a day. The water is much clearer, but I’m on day 10 and the nutmeats are still bitter and have turned a copper color. We do have well water with a high iron count but have a softener.

    At this point, I don’t know if that batch is a fail, or if I should keep leaching? I have a gallon of cracked acorns with the skins still on. How do I go about removing the testa before processing the rest of them? Any advice is appreciated!
    Thank you for your informative page!

    • Ellen says:

      Hi Karen, When I do a cold leach in a jar, I don’t shake it. Let it sit, drain once a day, then re-fill. Because you’ve already ground them, you won’t be able to remove the testas, but it’s possible the testas may float to the top if you don’t shake the jar, in which case you can pour them off with the water. Give it another 10 days and if they’re still bitter, toss the contents of the jar and consider it a learning experience. As for the gallon of cracked acorns with the testas still on, dry them in a dehydrator, after which the testas will fall off very easily. They’ll either fall off on their own, of you can rub them between your hands to remove them.

  10. Kal says:

    Hi there! I left my vitamix ground flour cold leeching in a jar, it looked normal for most of the day with nice separation between tannin water and sediment, but in the evening when i went to decant it off, the layers had flipped and the water layer was on the bottom. any thoughts on why this happened?

    • Ellen says:

      I’ve never seen that before and I’ve never heard of it happening to anyone else! Did you grind the acorns very fine? Hopefully someone here will have an idea about what happened, but I’d also recommend posting this (with photos if possible) on some of the foraging groups/pages on FB. You may get more eyes on it that way. And please let me know what you learn! Sorry I can’t be more helpful.

  11. Lisa says:

    Could you speak more of oxidation with acorns? I put a large amount of acorns through a DaveBuilt and it took some serious commitment and time to get them all out of the shells (red oak). By this point some of the outsides did seem to oxidize along the way. They are in the stage now of all the acorns mixed together having been cold leached (still in nut form) with two rinses a day for nine days. There is no bitter taste. Because I don’t know after all this work whether the oxidation is a problem with some of them, I am in need of a little more information. My family wants to go along with this acorn plan and at the same time I want the flour to be healthy for our bodies too.

    • Ellen says:

      I’m sorry, but I can’t say much about oxidation of acorns. It’s not something I’ve ever worried about, or heard any other forager worry about. Of course, because nuts are generally high in fats, they may turn rancid faster than other wild foods, which is why I store my acorns in the freezer at every stage (shelled, unshelled, ground, etc.) You mention that shelling them took a long time. How long did it actually take? If you shelled them and got them into the leaching water within a day, I would feel safe eating them. I’m guessing you saw some discoloration on the outside of the nut meat, is that why you’re concerned? I often notice the outside of the nut meat is darker than the inside, but that’s just as normal as the oxidation you see on an apple slice exposed to the air.

  12. Lisa says:

    Thank you so much for your quick response. I harvested about 15 pounds of acorns and it took about a week to go through every half and get the meat out. With the elections it was my way of literally going nuts while watching the news at night. I have a good sense of smell and nothing smells rancid or off with them. They did not taste bitter either. They are about ready to go in the dehydrator today or tomorrow. My learning this time was that I tried to do too many. Last year I did too little for the first time and this year the opposite. I am learning. My harvest was after a first big storm in the fall. There were endless amounts left for the animals even when I made the pile I did. They all sank and even after cold leaching nothing is floating except the testas. Also I believe it was too soon to process them. I dried them in the sun for a few days after harvesting and floating but it was really a task to get them out after I had cracked them open with the DaveBuilt. What a process! I have loved every minute of it however. It has been so helpful to have mentoring. Thank you very much.

    • Ellen says:

      You’re very welcome. Good that they smell and taste fine. You may be right that because they were prematurely knocked off the trees by the storm, they weren’t 100% mature. It’s possible this made them more difficult to shell. If you have another windfall year in the future, you could always put them in the freezer and process them in smaller batches. That might alleviate any worry about oxidation. Good for you for tackling the mighty acorn. It’s a benchmark for the serious forager.

  13. Lisa says:

    All right. I think that today is the day for the Excaliber dehydrator which I just borrowed from my daughter. There are a lot of shelves so I might be able to dry them all at once. I have never used a dehydrator before. I know that it shouldn’t be over 150 F. I am going to start looking online for advice on how long to put in dehydrator and at what temperature. It can be as low as 95 on it. After that it is acorn flour! And putting them what is left in the freezer. Nothing like hand-holding when one is a total novice. Your time with us is precious and I take your wisdom to heart. Thank you. Wish me luck.

    • Ellen says:

      Good for you! Once you’ve tackled the noble acorn, you’ll feel a great sense of accomplishment. It’s a lot of work, but totally worth it. I have an Excaliber and I dry my flour at 95F. It takes longer that way, but doesn’t cook the starch. Please let me know how it goes!

  14. Nancy Ball says:

    Hello,
    Collected acorns off Red Oak. Leeched in cold water for 3 days, then tried the boiling method and changed boiling water pot to pot about 6 times, then tired out and put in dehydrator. Tasted today not fully dry, and still a bit bitter. I just read about the testas and will try to remove, but the one I tasted was still a bit bitter.

    Will I get sick if I grind and use them with that bit of a bitter taste?

    Can I try grinding and leeching again ( the already leeched and dried nuts) or is the tannin already locked in?

    Thank you

    • Ellen says:

      Hi Nancy, Can you give me a little more info? When you leached the nuts in cold water for three days, were they whole but shelled? Did you leach them in running water (stream, toilet tank)? When I leach whole, red oak acorns it takes about a week in the toilet tank (i.e. running water). I’ve never cold leached whole acorns in still water, and I imagine it would take a very long time and you’d have to change the water every day. If I’m hot leaching I often do 10+ changes of water, so I’m not surprised you’re still tasting some bitterness. Most of the testas should have come off in the boiling, and those that didn’t should be loosened by drying. Those that don’t fall off into the bottom of your dehydrator should come off easily if you rub a bunch of acorns between your two hands. I can’t comment on whether you’ll get sick or not, but I can tell you that tannins impede the uptake of nutrition from your intestine. More important, I think, is that if they’re still bitter, do you really want to eat them? I would definitely try leaching again, to see if you can get that last bit of bitterness out of the nuts. If you grind them first, you’ll need to cold leach (because hot leaching ground acorns is a blobby mess). If you want to continue the hot leaching you can use the nuts whole. Whichever way you choose, be sure to remove as many of the testas as possible BEFORE you grind.

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