Acorns

As I am out walking at this time of year, whether in the woods or around the neighborhood, there is lots of crunching underfoot.  Acorns are one of the larger seeds littering the paths.  There are about 450 species of oak trees worldwide and almost 90 in the United States with 17 native to Illinois.

An acorn is a fruit and a nut and a seed.  Among Illinois species of oak trees, acorns grow between 5/16″ and 1-1/8″ in diameter, although many larger ones up to 3″ in diameter can be found in other parts of the world.  One quarter of the seed is covered in a cupule, a saucer shaped cup that may or may not be fringed around the edges.  The leathery shell, called a nut, is a hard, dry pod that surrounds a fruit with a single seed inside.  Oak trees are in the genus Quercus in the beech family, Fagaceae, and are split into two sub-genera, white oaks and red oaks.  White oak acorns grow to maturity each autumn when they fall off the trees.  Red oak acorns are produced yearly, but have a two year growth cycle before maturing and falling off the tree.

Mast is the accumulated fruit of trees and shrubs in forests, and acorns play an important part in oak-hickory dominated woods.  They are large, easy to find and eat, and are rich in nutrients including protein, fats, and carbohydrates, plus the minerals calcium, phosphate and potassium and the vitamin niacin.  White oak acorns are relatively sweet compared to the bitterness of red oak acorns.  Both contain tannins, a compound that makes food taste bitter and may be toxic in large quantities.  Animal species that eat red oak acorns typically cache them until water running over the cached nuts has leached out most of the tannin.  Acorns in the Midwest are a favorite food for duck, turkey, quail, pheasant, squirrels, chipmunks, deer and bear.

Acorns have never been used for human food on a scale reaching other nut varieties, but can be used for a variety of recipes.  In times of famine, they were a staple for Greek and Japanese cultures.  Korean noodles have been made from acorn flour since the early 1600s, while Ersatz coffee was made from large quantities of acorns during the Civil War.  Acorns, which contain starch, can be ground into flour for bread, pastries and pasta.  But all acorns require some leaching, involving soaking in several baths of clean water, to remove the tannins.  Hot-water leaching or boiling acorns can accomplish this in three to four passes, but it also removes the starch necessary to hold the resulting flour together.  Cold-water leaching takes a few days, but yields a better flour for baking.

Acorns are large and oak trees must rely on animals to move their seed around.  Scatter-hoarding is a behavior used by jays and squirrels that gather acorns and cache them for later consumption.  If the animal does not remember where all of its caches are, or it should perish before consuming all of the stored food, the remaining acorns have a chance to sprout and grow.  Every six to seven years, often referred to as mast years, oak trees will produce many times more than the usual number of acorns.  Current theory suggests that this is an attempt by the trees to overwhelm the consumers and increase the acorns chances of sprouting.  Take your favorite tree field guide and get out to a forest near you to see what acorns you can find and identify the trees that are nearby.