Acorns are divided into two main types for consumption: sweet and bitter. Acorns are the nut of the oak tree, and each type of oak has its own unique acorn.
There are over 400 species of oak trees native to the northern hemisphere, including over two dozen species in the United States. The acorns of the white oak are sweeter than the bitter black and red oak acorns. White oaks can be identified by the rounded lobes of their leaves, while black and red oaks have an identifiable point at the end of their leaves.
Acorns range in size from three-quarters of an inch to as large as four inches in diameter. Acorns mature in one to two years, dependent on the species. Nutritionally, acorns are comprised of about 50 percent carbohydrates, 35 percent water, and 5 percent each of fat, protein and fiber. These numbers are approximate because nutrient breakdowns vary by species as well.
Acorns contain a large amount of tannic acid that is damaging to the kidneys. Prior to consuming, acorns are leached to remove the tannins. This can be done by burying the acorns near a river bank, soaking the acorns in a rotating water bath for weeks or boiling. After leaching acorns are processed into flours and oils or roasted whole.