Leaching acorns

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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10 thoughts on “Leaching acorns”

  1. 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.

  2. 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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