Factsheet N04: Oaks with edible acorns
First, to dispel a myth: all oaks bear acorns which are edible. Most species of oak (of which there are many) produce acorns which are high in tannins, making them bitter and astringent when raw, hence they need processing to remove these potentially harmful substances. Removal of tannins is, however, extremely easy, taking no more time and effort than it takes to sprout seeds, and the resultant acorn meal resembles that from other nuts in oiliness and flavour.
There is a long history of human cultures using acorns as a food source, often as a staple crop. Early Greek writers referred to the acorn as a wholesome food. The most recent peoples to use acorns as a major food source were the native North American Indians, who used them widely well into this century. They are still a regular item of commerce in a few countries, notably Korea.