Acorn

An acorn is the single-seeded nut of an oak, set in a scaly cup and ranging from the size of a pea to a large olive depending on the species. The shell is smooth and tan to chestnut brown, and the kernel inside is cream to yellowish, hard, and starchy.

Taste varies greatly: white oak group acorns, such as those of Quercus alba or the cork and holm oaks of the Mediterranean, are mild to slightly sweet, while red oak group acorns are notably more tannic. Most acorns are sold shelled and dried, as flour or meal, as roasted kernels, as ground coffee substitute, and, in Korea and Japan, as starch for jelly. Sweet-kernelled holm oak acorns can be eaten roasted with little processing.

Oaks (genus Quercus) grow across the temperate Northern Hemisphere and into tropical mountains of Central America and Southeast Asia, with about 400 or more species. Acorns have been gathered by people since prehistory in Europe, Asia and North America, and archaeological sites show intensive acorn processing long before agriculture.

The English word acorn comes from Old English æcern, with relatives across Germanic languages, and was reshaped by folk etymology into oak and corn. The genus name Quercus is the Latin word for oak.

Acorns fed people across the world for thousands of years. In California, many Indigenous nations built whole economies on acorns, pounding the kernels into meal in stone mortars, leaching the meal with water to remove tannin, and cooking it as mush, soup or bread. Comparable traditions existed in eastern North America, Japan, Korea, China and the Mediterranean. Jomon-period sites in Japan hold evidence of acorn storage pits and processing.

In Europe, acorns served as famine food and animal feed. The classical world praised the sweet acorns of certain Mediterranean oaks, and in Iberia the dehesa system, an open woodland of holm and cork oaks, has long supported pigs that fatten on acorns, producing the cured ham known as jamón ibérico de bellota.

As wheat and later potatoes became staples, acorns declined as a mainstream food but never disappeared. During wartime shortages, acorns were roasted and ground as a substitute for coffee in parts of Europe. Korea still makes dotori-muk, a set acorn starch jelly. Interest in wild and Indigenous foods has also led to renewed attention to acorn flour among foragers, chefs and Native American food sovereignty projects.

Leached acorn meal is used as flour in breads, pancakes, porridge and gruel. Cold-leached or boiled acorns are roasted and eaten as a snack, ground as a caffeine-free coffee substitute, or processed into starch for jelly, noodles and tofu-like cakes in East Asia. In Spain and Portugal, acorns are the key feed for free-range Iberian pigs.

Traditionally, acorn cups and bark were used for tanning leather, and acorns have served as livestock feed across Europe and North America. In Korea and parts of Japan, acorn starch is also set into jellies, noodles and savoury cakes served cold with soy-based sauces.

Acorns are an energy-dense nut with starch and unsaturated fat, and they have long supported populations when other foods were scarce. Their notable feature is tannin, which is removed by repeated leaching in water; properly prepared acorn meal is a historically safe staple. Modern health claims for acorn flour are not well documented in clinical trials, so it is best treated as a traditional, nutritious wild food rather than a medicine.