Saturday, December 14, 2013

Percolation leaching Red Oak acorns

Just a few of these hefty acorns make a handful
It has been several years since I collected Red Oak (Quercus rubra) acorns, and never in the Pacific Northwest. This year they masted heavily near my house and my Garry Oak supply just ran out, so I figured it was time to reconnect with the first acorn I ever ate. Last month I collected 5 gallons of large acorns in just a few hours, and have recently just finished drying and shelling them. This post includes a detailed description of Red Oak along with some ethnobotanical notes, and my experiment with a new (to me) method of leaching acorns.

Red Oak in its native range along the Wisconsin River
Wild Red Oak populations range from Minnesota eastward to Nova Scotia and southward from eastern Oklahoma through most of Alabama, and the northern half of Georgia, South Carolina and North Carolina. Two varieties are currently recognized by botanists: Q. rubra var rubra has a more southerly distribution and larger, rounder acorns, and Q rubra var borealis has a more northerly distribution and smaller, more oblong acorns. Though not native to the Pacific Northwest, Red Oak are frequently planted at college campuses, cemeteries, and along streets. They are actually far more common near my house than our native Garry Oak (Quercus garryana).

Brilliant foliage on a fine fall day
In our region, Red Oaks trees generally have straight trunks with spreading to upright branches and a rounded crown. They mature to 60-90 feet tall and can grow 4-6 feet in diameter, but as most of those in the Pacific Northwest are less than 100 years old, trees greater than 3 feet in diameter are rare, despite rapid growth rates.

Red Oak bark
Bark is grey and cracks into relatively smooth plates separated by long, shallow, vertical fissures.
Twigs are reddish brown and smooth. Buds are reddish brown, egg shaped, and ¼ inch long. 

The deciduous leaves arise alternately on the branch and range in size from 3-12 (15) inches long and a little more than half as wide. Margins have pointed tips (like all oaks in the red oak group) with 1-5 sharp teeth on each of the 5-9 (usually 7) evenly space lobes with u-shaped troughs that extend a third to half the distance towards the midvein. Leaf bases taper abruptly to a ¾-1.5 inch long petioles. Fall foliage ranges from yellow to scarlet to bronze and some trees will hold dead leaves into the winter. Upper leaf surfaces are smooth and slightly glossy, and lower surfaces are smooth with conspicuous veins that are sometimes hairy.

A lineup of leaves

Red Oak acorns are the quintessential North American acorn with a fairly round shape and shallow saucer to cup shaped cap. Shells range in size from 5/8- 1 1/8 inch wide and 1-1.5 times as long. Shell color ranges from yellowish brown to green to purplish red, and the shells are sometimes covered with very fine silver hairs. Caps only cover 1/3-1/4 of the shell or less, and have a scaly top.

Size gradation of two Red Oak acorn varieties

The US Forest Service Fire Effects database reports that Red Oak acorns contain 1300 calories per pound with roughly 5 percent protein. Kuhnlein and Turner (1991) found 7.2 g of protein, 14.5 g of fat and 65.7 g of carbohydrate per 100 grams of fresh acorn. However, acorns are high in tannins with levels ranging from 4-16 percent.
Eaten as a staple food by the Anishinabe (Ojibwa), Dakota, Haudenosaunee (Iroquois), Omaha, Pawnee, Ponca, Potawatomi (see Native American Ethnobotany) and likely all the Indigenous Peoples living within the plants range. The bitter tannins are traditionally leached with the aid of wood ash or lye and cooked into gruel.

Smith's image of edible acorns species
Early ethnobotanist Huron Smith (1923, pg 66) documented the Menominee method of processing various oak species: "The hulls were flailed off after parching, and the acorn was boiled till almost cooked. The water was then thrown away. Then to fresh water, two cups of wood ash were added. The acorns were put into a net and were pulled out of the water after boiling in this. The third time, they were simmered to clear them of lye water. Then they are ground into meal with mortar and pestle, then sifted in a birch-bark sifter. The fourth time, the meal is cooked in soup stock of deer meat until finished and ready to eat, or made into mush with bear oil seasoning. The old Indians never made pie, but the Menomini now make pie of them."

Shelled Red Oak acorns

Cracked acorns
I’ve written previously about how I dry, crack, and winnow my acorns (see How to Eat an Acorn), but I thought I would pass on another leaching method that Sam Thayer recently told me about called percolation leaching. The technique is modeled after California Native American acorn leaching whereby finely pounded acorn flour is placed on a shallow depression in the sand that is repeatedly filled with water. 

Cracking acorns with a Davebilt Nutcracker

Hupa woman leaching acorns in sand. Photo from Goddard 1903
I have read reports that this technique was capable of leaching tannins from the California acorn species in a matter of hours, but had assumed that such short leaching times had more to do with how the tannins were bound in the California acorns than the leaching method. However, Sam informed me that he was able to leach acorns that normally took the better part of a weak using the decanting method in less than a day with the percolation technique.

My new percolation leaching device
Grinding Red Oak acorns
Percolation leached acorn flour
My first attempt proved equally successful so I constructed my own acorn percolator with a two plastic buckets and a flannel sack. I sliced the bottom off a 2 gallon bucket and cut a hole in the lid of a 5 gallon bucket just large enough for the bottom of the 2 gallon bucket to fit inside. Then I fitted the flannel sack to the lip of the two gallon bucket and filled the sack with acorn flour and water. In the time in took to percolate about 5 gallons of water, I leached half a gallon of acorn flour. There is no going back now. Percolation leaching outperforms decanting hands down.

Drying acorn flour
This new method allows me to leach more acorn flour than I can use immediately, so I have been drying it in a food dehydrator and regrinding the clumps that form to make a soft, very fine flour that is ready to use at a moments notice. Because it is higher in oil than most other flours, I store my acorn flour in the freezer so it doesn't spoil.

Finished Red Oak acorn flour

Native American Ethnobotany

Smith, Huron 1923. Ethnobotany of the Menomini Indians, Bulletin of the public museum of Milwaukee 4(1):1-174. Photo plates can be seen here.

Dunham, Sean B. 2009. Nuts about Acorns: A Pilot Study on Acorn Use in Woodland Period Subsistence in the Eastern Upper Peninsula of Michigan. The Wisconsin Archeologist 90(1&2):113-130

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  1. I'm looking forward to some fresh red oak bread soon! Also, I think the leaves make wonderful leaf mold compost. I usually have a pile going all the time, finished leaf mold in 2 years when I start the leaves the first year in heavy duty black plastic trash bags. I do the city a favor and rake some of their leaves into my bags...

  2. This is incredible! In the tropics there has been a push to make flour from abundant wild fruits and my favorite is the peach palm flour, although the taste is a little strong and overpowering. What does this acorn flour taste like?

  3. Acorn flour has a pleasantly sweet and nutty flavor. It smells very much like molasses or caramel.

    Peach palm flour sounds scrumdiddlyumptious!

  4. Nice percolator! Where did you get the flannel sack?

  5. I purchased it from a maple syrup supply store online. Search "Flannel Filter." You could easily make your own, which is what I will do if I need any more.

    1. Hi Abe, I read your article with eager interest from the other side of the Atlantic (the Netherlands) I have recently been more seriously occupied in processing, eating acorns. I was wondering what is the best way to make such a filter yourself. Did you have any findings recently? thanks for the nice blog

  6. Thank you! Great demo it will be very helpful for me to leach my tanoak acorns

  7. Interesting.... will give this a go this week. I have lots of dried acorns I store throughout the year.

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  10. I am very interested in trying this method, but have a question for you:
    Does the starch wash out? I currently cold leach by decanting, and that pale starch layer is like gold to me. It really helps to bind flour for tamales, polenta, etc. We gathered a huge glut of acorns this past season, and really are curious about a more time/bulk efficient leaching method.

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