The eastern oaks that yield sweet mast are the basket, black jack, bur, chestnut, overcup, post, rock chestnut, scrub chestnut, swamp white, and white oaks, the acorns of chestnut and post oaks being sweetest; those producing* bitter mast are the black, pin, red, scarlet, shingle, Spanish, water, and willow oaks; of which the black and water oak acorns are most astringent.
None of these can be used raw, as human food, without more or less ill effect from the tannin contained. But there are tribes of western Indian who extract the tannin from even the most astringent acorns and make bread out of their flour. The process varies somewhat among different tribes, but essentially it as as follows:
The acorns are collected when ripe, spread out to dry in the sun, cracked, and stored until the kernels are dry, care being taken that they do not mold. The kernels are then pulverized in a mortar to a fine meal, with frequent siftings to remove the coarser particles, until the whole is ground to a fine flour, this being essential. The tannin is then dissolved out by placing the flour in a filter and letting water percolate through it for about two hours, or until the water ceases to have a yellowish tinge. One form of filter is contrived by laying a coarse, flat basket or strainer on a pile of gravel with a drain underneath. Rather fine gravel is now scattered thickly over the bottom and up the sides of the strainer, and the meal laid thickly over the gravel. Water is added, little by little, to set free the tannin. The meal is removed by hand as much as possible, then water is poured over the remainder to get it together, and thus little is wasted. The meal by this time has the consistency of ordinary dough.
The dough is cooked is two ways: first, by boiling it in water as we do corn-meal mush, the resulting porridge being not unlike yellow corn-meal mush in appearance and taste; it is sweet and wholesome, but rather insipid. The second mode is to make the dough into small balls, which are wrapped in green corn leaves. These balls are then placed in hot ashes, some green leaves of corn are laid over them, and hot ashes are placed on the top, and the cakes are thus baked.
(Coville, Contrib. to U. S. Herbarium, VII. No. 3. Palmer, in Amer. Naturalist, XII, 597. Another method, used by the Porno Indians, who add 5 per cent, of red earth to the dough, is described by J. W. Hudson in the Amer. Anthropologist, 1900, PP. 775-6).