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: flushing water (cold leaching) and boiling water (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 roasted snack burger patties, acorns, 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.