Acorn

• 1. Introduction

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  The acorn, the nut of the oak, takes anywhere from 5 to 24 months to ripen, depending on the species. That is a long wait for a seed that so many hungry creatures are ready to eat. Yet the wait is part of a bargain between a tree and everything that lives beneath it.

  The bargain raises odd questions. Why does a nut this bitter feed so many mouths? How does a tree with such heavy seed ever spread beyond its own shade? How did people learn to turn it into bread? And why does this small object appear on cutlery, on soldiers' hats, and on footpath signs?

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• 2. Name and Anatomy

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  Chaucer, writing in the 14th century, spoke of the "achornes of okes". His spelling hints at how restless the word has been.

  Earlier forms of the word included akerne and acharn. They are related to the Gothic akran, which meant "fruit of the unenclosed land". Over time the word settled on the most important thing the forest produced, the fruit of the oak.

  Speakers then bent the word toward things they already knew, linking it to corn and to oak-horn. The spelling shifted to match, and the modern form emerged around the 15th or 16th century. It joins ac, the Old English word for oak, with corn.

  Another name for the acorn is glans, a Latin word that originally applied to any nut. That root gave French gland, Catalan gla, and Italian ghianda. All are cousins of the Greek balanos.

  Botanically, the acorn belongs to the oaks and their close relatives in three genera: Quercus, Notholithocarpus, and Lithocarpus. All three sit in the family Fagaceae. Inside is usually a seedling wrapped in two cotyledons, which are seedling leaves. A tough shell called the pericarp encloses it, and a cup-shaped cupule holds the whole package.

  Shape and ripening time are among the clues botanists use to tell oak species apart.

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• 3. A Feast for Animals

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  In Spain, Portugal, and the New Forest region of southern England, pigs are still turned loose each autumn in large oak groves. In Spain and Portugal these groves are called dehesas. The pigs fill and fatten themselves on fallen acorns.

  Deer take part in the same harvest. In autumn, acorns can make up as much as 25% of what a deer eats. Bears and pigs also consume large quantities.

  Birds join in too, including jays, pigeons, some ducks, and several species of woodpecker. Mice, squirrels, and other rodents feed on the crop as well. One beetle, Thorectes lusitanicus, eats acorns too.

  Some feeders never touch the fallen nut. The larvae of certain moths and weevils live inside young acorns and eat the kernels as they develop.

  The size of the crop swings widely from year to year. Acorns and other nuts of this kind are known as mast. A bumper year brings abundance, and a poor one brings real stress for the animals that depend on them and for the predators that hunt those animals. Large yields also help small rodent populations grow.

  Animals value acorns because they are big enough to be eaten or stored efficiently. They are also nourishing. Every species of acorn holds plenty of protein, carbohydrate, and fat, along with calcium, phosphorus, potassium, and the vitamin niacin. Their energy content compares well with other wild foods and other nuts.

  But the same nut carries a chemical defense, and not every animal can cope with it.

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• 4. The Tannin Problem

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  Horses and cattle can be made ill by eating too many acorns, because they cannot detoxify the bitter tannins inside. When cattle metabolize those tannins, the resulting tannic acid can cause ulceration and kidney failure.

  Tannins are plant polyphenols, and they interfere with an animal's ability to metabolize protein. The amount varies from one oak species to another. Some animals cope by choosing acorns with fewer tannins, and others buffer their diet with different foods.

  Jays and squirrels that cache acorns may wait before eating them. Once enough groundwater has percolated through the buried nuts, much of the tannin washes out. Many insects, birds, and mammals handle tannins with fewer ill effects than humans do.

  People notice the difference at the first bite. The acorns of American red oaks and English oaks are very bitter, astringent, and potentially irritating when raw. White oak acorns carry far less tannin and taste nutty, and a light roast before grinding brings out that flavor.

  The cure for bitterness is water. Chopped acorns can be soaked through several changes of water until the water stops turning brown. With cold water this takes several days. Three to four changes of boiling water can do it in under an hour.

  Boiling has a side effect. It cooks the starch, and that starch would otherwise act like gluten in flour, helping the meal bind to itself. So a cook who wants flour should leach with cold water instead.

  The finished flour is rich in fat, so it can spoil or turn moldy easily and needs careful storage. Acorns are also sometimes prepared as a massage oil.

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• 5. Planting by Forgetting

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  Jays and squirrels do the oak's traveling for it. Acorns are too heavy to ride the wind, so oaks depend on animals to carry them beyond the mother tree to a spot with enough water, sunlight, and soil nutrients.

  Most animals that eat acorns, whether unripe on the branch or ripe on the ground, give the oak nothing in return. Jays and squirrels are different. They scatter-hoard, burying caches in many separate places, and in doing so they effectively plant acorns where seedlings can germinate and thrive.

  Both animals keep remarkably large mental maps of where their caches lie. Even so, the odd acorn is lost, or a jay or squirrel dies before eating its whole store. A small number of those acorns germinate and survive to become the next generation of oaks.

  The arrangement has limits. Scatter-hoarding works because the nut is valuable food but not too big for the animal to handle. For jays, beak size decides how large an acorn can get before the birds ignore it.

  Timing matters too. Acorns of the white oak group, Leucobalanus, begin rooting as soon as they touch soil in the fall and send up a leaf shoot in spring. Other acorns follow different schedules, depending on their place in the oak family.

  Once an acorn sprouts, it becomes a poorer meal, because its seed tissue converts into the indigestible lignins that form the root.

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• 6. An Old Staple

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  Dental microwear suggests that Neanderthals in Belgium ate acorns among other hard foods. Later cultures leaned on them too, including the lower classes of Ancient Greece and the Japanese of the Jōmon period. The Roman writer Pliny the Elder noted that acorn flour could be used to make bread.

  Today acorns rarely form a large part of any diet, and they are not cultivated on a scale anywhere near that of many other nuts. Grains have largely replaced them, except in some Native American and Korean communities. Properly prepared acorn meal can still stand in for grain flour in some recipes, if cooks pick good specimens and leach out the tannins.

  Oak varieties differ in how much tannin their acorns hold. Quercus kelloggii, the California black oak, was preferred by Native Americans and may be easier to prepare or more pleasant to eat. In Kurdish areas of Iran and Iraq, roasted acorn flour is a main ingredient in special sweet cakes.

  The numbers are plain. Raw acorns are 28% water, 41% carbohydrate, 24% fat, and 6% protein. A 100 gram portion supplies 387 calories, and it is a rich source of vitamin B6, folate, copper, and manganese.

  Acorns are a traditional food of many indigenous peoples of North America. They long mattered most to Native Americans in California, where the ranges of several oak species overlap and make the harvest more dependable. Several cultures developed their own leaching methods, sometimes with specialized tools, and passed them to their children by word of mouth.

  An ecology researcher of Yurok and Karuk heritage reports that "his traditional acorn preparation is a simple soup, cooked with hot stones directly in a basket." He enjoys acorns eaten with "grilled salmon, huckleberries or seaweed."

  In the San Francisco Bay Area, acorns found at sites were often associated with grinding tools. A hammerstone and anvil could crack the shell, and millingstones or a mortar and pestle could grind the kernel into dust.

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• 7. Symbol of the Oak

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  Classical writers linked acorn-eating, known as balanophagy, with primitive life and with Arcadia, and the association outlasted antiquity.

  The acorn itself became an ornament. It is a motif in Roman architecture and was also popular in Celtic and Scandinavian art. Craftspeople have placed it on cutlery, furniture, and jewelry, and it appears on finials at Westminster Abbey.

  During the American Civil War, both Union and Confederate forces used the acorn frequently as a symbol. Traces of it survive today on the campaign hats of US Army Cavalry Scouts.

  Heralds have long used acorns as charges in heraldry. The University of Connecticut also carries an acorn in its symbol, specifically that of the white oak.

  On the National Trails of England and Wales, walkers still find their way by following acorn waymarks.

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