The acorn could practically overnight become the most used nut in the Nordics. The reason is that there are already today hundreds of thousands of oaks of nut-producing age - it's just a matter of starting to harvest. In many parts of the world there were cultures that had acorns as a staple food. In the Nordic countries, acorns are considered inedible by most people today, but during the Stone Age the nuts of the forest oak may have played an important role in people's diet. Acorns are rich in carbohydrates, protein and to varying degrees also fat.
Acorns can be used in many different ways. They can be ground into flour and used in all imaginable baked goods. They can be coarsely chopped and added to soups and stews or to make steaks. Porridge can be cooked on crushed acorns and it is even possible to ferment acorn paste into something similar to cheese. In Korea, liqueur is made from acorns (dotori-sul) and the starch found in the acorn is used to make noodles (dotori-guksu) and acorn tofu, called dotori-muk. Roasted acorns can work as a coffee substitute. It is also possible to extract a valuable edible oil from the fattier types of acorns, which is most easily done with the help of a small hand cranked oil press. Both the taste and the chemical composition are comparable to olive oil, but the oil needs to be kept cool to stay fresh.
The major challenge with acorns as a staple food is that they contain tannins that make the nuts of most species inedible without first processing them. The tannins have many health-giving properties and are found in many foods such as tea, coffee and red wine, many pea plants, fruits such as apples, pears and bananas as well as most berries. In large quantities, however, they reduce appetite, inhibit the absorption of other nutrients and, if over-consumed for long periods, can even be toxic. Generally, a tannin content of over is considered 2% of the fresh weight be a deterrent for most mammals, including man. The tannin content of most of the oaks we can grow in our climate is above this limit, but varies greatly between species, between different years (stressful years, the tannin content is higher) and also between individuals within the same species. Even within each acorn, the tannin content varies, where the tip can be significantly sharper than the end. It has been observed that both rodents, birds and insects prefer to eat the end of the acorn (closest to the fruit bowl) and in those cultures where acorns are still part of the diet, it is customary to cut off the tips of the nuts when they are eaten fresh.
The tannins thus need to be removed to a certain extent to make the acorns edible. This can be accomplished in several different ways. Since most of the tannins are water soluble, most methods are based on using water to remove them. The simplest and most common methods are cold- respectively hot leaching. At of kallurlak cold water is used for a longer period to treat relatively finely crushed acorns. Varmurlak's with warm water goes faster, but requires a little more presence (and energy) than cold leaching. Traditionally, various chemical methods have also been used. In California, a dry leaching method was used, where red clay (rich in iron oxides which can bind tannins) was mixed with acorn flour to make a variant of flatbread that was baked for half a day to neutralize the tannins. In Sardinia, the same kind of red clay was used, but there it was dissolved in water to make the hot leaching more effective. Pot ash was also used by many cultures to bind some of the tannins during leaching.
This post is an edited excerpt from the award-winning book “Nut grower's manual” by Philip Weiss (2022).