Acorn leaching process

Acorn trees

Table of Contents

About the leaching process

Following my post on acorns and before you run out to your nearest oak tree, it’s important to remark acorns are naturally bitter and they must be processed to make them palatable. This unpleasant flavour comes from the tannins, which can be astringent and damage our kidneys over time.

Tannins are removed through a process called leaching, whereby the acids are drained away from the acorns using water. Afterwards, is completely safe (and tasty!) to eat these intriguing nuts.

Considerations before you start

There are quite a few ways to leach the tannins, but it can be summarised into two: cold leaching and hot leaching. The method you want to use is determined on what you want to do with the acorns afterwards.

The temperature at which you process the acorns is important. Boiling or roasting precooks the starch and therefore cannot be used as a binder in any recipe. On the other hand, cold leached acorn meal will thicken when cooked, as eggs would do.

Use hot leaching method for a roasted acorns snack, burger patties, mock coffee, brittle or added in stews. Alternatively, cold leaching method is best suited for baking flour. Please note you can still use hot leached acorn for baking, but you will need to add some extra binder.

Remove shells before leaching: use a pair of gloves and a very sharp knife to cut the husks and remove the acorn meal. It’s fine to chop them in quarters if you intend to use them as flour or coffee. They are easier to cut like that and are faster to dry and leach than whole acorns.

Cold water leaching

In the nature, squirrels bury acorns in the ground and leave them there for a long period of time, so rain and running water make the leaching work naturally. This method tries to replicate it in a controlled environment.

Crush the acorns into small pieces or grind them into a coarse meal, as this makes the process quicker. Make sure to remove as much brown skin as possible before grinding, as it is quite bitter.

Soak your chopped acorn in many changes of water until it runs clear or the acorn does not taste bitter anymore. Let it set, then strain, repeating the process all over again. The leaching can take anywhere from 1 day to 1 week. Don’t let it stagnate for a single day or this will spoil your mix.

Alternatively, place your chopped acorn in a muslin or cheesecloth over a basket in your sink. Massage gently and keep the water running constantly till you find they are not bitter anymore. It works really quick comparing to the other method, but some flour and oils will be leaked with the movement.

Now, the acorn meal is ready to use as baking flour, which will need further preparation. You can read here.

Hot water leaching

Following this method you will boil off the oil with the tannins and the flavour will be a bit sweeter.

Place your shelled acorns in a pot with cold water and salt, bring it to boil and simmer for 30 min. The acorn skins will detach and float, so they can be easily removed using a skimmer. In the meantime get a second pot with boiling water ready.

When the water darkens, pour the water and acorns into a colander and put the hot acorns in the second pot with fresh boiling water. Never at any point place the acorns into cold water, as this will bind the tannins, so they will remain bitter. Keep changing pots for a third and fourth time and they will be ready as soon as the water runs clear.

Leached acorns can be used right away in your desired recipe, but can also be dehydrated, pickled in salted brine or frozen for future use.


At this point you might be reading this and thinking this involves a hell lot of work. Of course it does, but foraging is a lifestyle and you are doing this because you enjoy experiencing new flavours, learning new skills and using nature’s resources. Acorns are high in nutrition and contain starches, something difficult to forage for.

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Alvaro Docio

Alvaro Docio

I am the person behind British Local Food. As a forager and wild food educator, my aim is to inspire you to go outdoors, familiarise with your local plants and make the best of their culinary and medicinal properties, in the hope you'd pass on any knowledge gained down to the next generation.

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24 thoughts on “Acorn leaching process”

  1. I collected acorns from an English oak in October, chopped them up into small bits, have been leaching them in cold water ever since with 2-3 water changes per day, and they are still bitter. Did I miss the window and they’ve gone bad? Or is more time still needed? Please advise!

    • Hi Katie,
      It’s difficult to tell what’s going wrong, it could be a lot of things! Did you remove the outer brown skin before submerging in water? Did you let the acorns stagnate in water for a day at some point? Were the pieces small enough? Could that be a different oak species?

      This process normally takes 1-2 weeks, but leaching them for months seems a bit too much, so perhaps they got spoiled?

      Bear in mind that they will never become sweet after cold leaching, as the process just removes the bitter tannins. It’s after baking with the flour that they release natural sugars and become sweeter.

  2. Greetings, Mr. Docio. Thank you for the time and effort you have put into this article.

    I found myself with some less-than-stellar acorns this year. After drying and shelling, I find most are stained a dark brown to black. I assume this is (are?) tannins from the shells and am cold leaching them. Most of the color is coming out. Should I continue to leach the nut halves until the the water remains clear or stop when no bitterness is detected?

    FYI: this is a for fun project. If nothing else I will leach, dry, and feed them to the squirrels. Thank you.

    • Hi Joe,
      Acorns should not be black after dried, I am concerned they might be mouldy, perhaps?
      Generally, acorns dye water into a brownish colour and you should continue to leach until the water remains clear, ideally when no great deal of bitterness is perceived.
      If unsure, squirrels will appreciate them anyway. 😉
      Have a nice day!

  3. Hi!
    Okay, I have been collecting my acorns over the past two or three weeks….. and guess what?…I am reading your article, Alvaro, and trying to decide which leaching process to choose….only to discover that half of my acorns have now sprouted! Is it still worth having a go? And if so, which process would you try? Hot water?

    • Hi Lesley,

      Acorns change internally once they have sprouted. Starch turn into sugars, the texture becomes more rubbery and the nutrients change.
      They can still be processed and eaten, but the result will not be the same as for just ripen acorns.
      I would go for hot leaching and enjoy them as snacks, pickles or in soups, just because I think cold leaching for flour is not worth trying in this case.
      Hope it helps,


  4. Have you ever tried Oak leaf wine?I made it and it tasted very good.I take it that the tanins in the leaves gave it the body that a white wine needs.It didn’t require the the same process of boiling like Acorns do.I boiled the leaves first to extract the flavor.

    • Hi Richard,
      I have never tried oak leaf wine, though it sounds like a good idea. I guess it can be used as a shortcut to storing the liquid in oak barrels while resulting in a slightly different profile.

  5. Hello! I’m learning to leach acorns as a surprise for my mother. She has several trees at her new house but has no idea what to do with them. Does any one know how long after hot leaching and then roasting that they would stay good? I’m trying to time it to go with her Christmas this year! Thanks in advance!

    • Hi Emma,
      It may depend on the particular acorn species and other factors.
      Generally, you’d expect something in between 2 to 4 changes of water.
      Try one piece everytime you change them and you’ll find out when they are ready.

  6. Hello,

    I am using a new hot leaching method that includes adding baking soda to the water to speed up the leaching process.

    The comment on the other website where I saw that didn’t spell out the reasoning, but I’m guessing that changing the chemistry of the leaching water draws the tannins out faster by binding to them. This appears to be working beautifully, as I am only on the third boil, and this one may actually not be necessary! I filled up the pot this time before I tasted the nuts, since I am used to having to do many more boils. The boiled acorns have turned dark, but are not bitter at all now.

    For the first time however, I noticed that there are little droplets of what I think is acorn oil on top of the leaching water. Perhaps that was happening before, and I just failed to notice it. Your website mentioned that the hot process will leach out acorn oil with the tannins. Am I losing nutrients by doing that?

    Your site also states that if I use hot process leaching to make flour, I will need to add a “binder.” This is the first I’ve heard of that. What is a “binder,” as the word is used here? Please give an example of an additional ingredient and process in acorn bread making, since that’s what I leach the acorns for.

    I always use the hot process, both for speed and because I don’t have a stream or easy access to a flowing water source. I once had an unattended small batch go bad as you described when I put them in a bucket of cold water and forgot about them.

    Since I know that the acorn shells have tannins as well, I thought about concentrating them for use in a friendlier skin tanning operation. Oak bark is non toxic, as opposed to the current high tech method metals method, which is massively environmentally polluting. Research has shown that the old oak skin tanning method requires 120 pounds of powdered oak bark per cowhide, and that’s a lot of dead oak trees!

    Since stripped, dead oak trees is almost as bad a result as commercially poisoned water, I’d like to make a suggestion for the photographer who asked about concentrating tannins, even though he’s using it as a photo fixer and not to tan hides.

    Shell the acorns, and put them in a large tub of water outside, either cold processing or over a fire, hot processing them. Process the acorn meats separately for consumption, and throw the wastewater into the acorn shell processing bath so you’re adding the nut tannins to that. No waste! either boil of the water or allow the Fall sun to evaporate the excess water, which would concentrate the tannins. Once you have the proper concentration, you’d have photo fixer, or in my case, non tree killing, non metal toxic skin tanning solution.

    I know this is a lot for one comment, but I look forward to seeing what you have to say on all of my points, starting with the acorn oil / nutrition /binder issue, which for me is the most important of the questions.

    • Hi Laurie,

      -Never heard about using baking soda, but I am sure I will try.
      I still have a batch waiting for processing.

      -Hot leaching will remove the oil with the tannins and therefore reduce the nutrition that comes from the fatty acids. On the other hand, your flour would last longer, because a high oil content can make it rancid over time.

      -However acorn flour should be made from cold-leached acorns, otherwise the heat would cook the starch. You need this starch to form a cohesive mass made from the flour, water and oil so you can shape your dough. If you use hot-leached acorn flour I would recommend you add regular wheat flour in the mix to help shape your dough. It will still retain the sweet nutty flavour of acorn bakes and the flour will go a long way.

      -I really appreciate your advice on the tanning solution, which I am really sure will be of big use to the poster below.

  7. Hi!

    I would like to leech out the tannins and use the tannin infused water as a toner in an alternative photography project, therefore I would like quite a heavily infused tannin water. Are there tannins present in the shell/skin or should I just use the inside part? Time isn’t an issue so I don’t mind doing either the cold or hot method, but which is likely to remove the most tannins and then retain the tannins in the water ? I imagine grinding or breaking the acorns prior to leeching would be the most thorough way to extract the tannins?

    • Hi Mark,
      I have never used tannins as a natural ink, so I am not sure about the best procedure.
      Tannins are present in the wood, bark and acorns of oak. For you purpose, I would soak the organic material in water for as long as possible.
      You might also consider using unripe walnuts or tea leaves, which also contain high levels of tannins.

    • Hi Geri,
      Acorns are totally safe as long as you follow leaching instructions, the same way you should not eat uncooked butter beans or raw potatoes.
      There is no reason to be scared. You can even eat a raw acorn or two with no ill effects. However they are so bitter when unprocessed that you will not want to anyway!

    • Hi Nicky. Acorns eaten as nuts are naturally sweet but those rarely grow in the UK. If you still want to eat them as nuts and you cannot find the right species, I would recommend roasting them in the oven after leaching. The method is up to you. Generally speaking, hot leaching is quicker but the result will be a bit mushier. Cold leaching is very slow as it can take days, but you will get the crunch.

  8. Hi!
    I have made mock coffee after following a blog. It suggested you could boil the acorns with the shell on for 20 mins to remove tannins.
    Then cool, shell, dry for 24 hours, chop and roast.

    Is this okay? Or will there still be tannins in the acorns using this method?



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