Thursday, November 1, 2012

How to Eat an Acorn

Oak Harbor's crop of acorns
Cool weather and wind have driven most of the Garry Oak (Quercus garryana) acorns from the  trees. Time to pick them up and make food! I recently went down to Oak Harbor to gather acorns, and in the time since then, the pleasant aroma of drying acorns has inspired me to write a more comprehensive post about our native acorns.

A venerable specimen next to Sauvie Island (Oregon)
Also called Oregon White Oak, Garry Oaks are the only oak tree native to Washington and British Columbia. Oak woodlands and oak savannas are found in lowland valleys, gravely slopes, rocky outcrops, and dry plateaus from southern Vancouver Island southward, through western Washington and Oregon, and down to central California. At the northern end of the their range they are only found below about 2,000 feet, but as you move southward their range extends up to about 4,000 feet above sea level. Garry Oaks begin to mingle with Black Oaks (Quercus kelloggii) and Canyon Live Oaks (Quercus chrysolepis) at the south end of the Willamette Valley, and Blue Oaks (Quercus douglasii) and Valley Oaks (Quercus lobata) in Northern California, and then finally, Coast Live Oaks (Quercus agrifolia) near the Bay Area. You may also find Northern Red Oaks (Quercus rubra), Pin Oaks (Quercus palustris) and English Oaks (Quercus rubor) planted as street trees throughout the Pacific Northwest.

Blocky bark on an old Garry Oak
Garry oaks can reach great proportions when they grow in deep soils that are free from competing Douglas Firs. Of our western oaks, they are second in size only to Valley Oaks and occasionally reach 90 feet in height. However, on dry rocky soils and in areas with little precipitation, they take on a low scrubby form. Most commonly they are between 50 to 60 feet tall and 6 to 24 inches in diameter (See Sudworth’s “Forest Trees of the Pacific Northwest”). Garry Oak branches are often twisted and gnarled and their trunks can sprawl wildly. The mature bark is light grey with deep blocky fissures. Twigs are hairy when young. The leaves are 3.5 to 6.5 inches long, deeply lobed, and are shiny green on top and pale green below with somewhat of a leathery texture. They begin to fall around the end of September but take several months to drop all of their leaves.

The upper (left) and lower (right) surfaces of a Garry Oak leaf
Garry Oak acorns mature in one season. Acorns arise in groups of 1-3 and are relatively round, with the widest part at or slightly above the middle of the acorn. They are usually 1-1.25 inches long and 0.625-1 inch wide. Freshly fallen acorns will often still be green, but mature to a reddish brown. Caps are warty and only cover the upper 20% or less of the acorn.
A spectrum of Garry Oak acorn sizes (with a ruler showing cm)

Yikes, this acorn had a wriggly passenger!
The first wave of acorns begins to fall in early September, but these should be ignored by harvesters as they are almost always infected by acorn weevils. Ideally, the ground would then be burned or raked to clear away the diseased acorns in order to disrupt the acorn weevil reproductive cycle and facilitate faster picking when the mature acorns begin to drop. Typically healthy acorns fall from from late September to early November. Burning isn’t usually possible, so acorn harvesters need to know how to distinguish good acorns from bad. Sam Thayer devotes considerable attention to this topic in his book “Nature’s Garden”. To summarize, here are a few things to avoid: (1) acorns that still have caps, (2) acorns with small pin sized weevil exit holes in them, (3) acorns with shells that are separating from the disc at the top (where it attaches to the cap), (4) acorns with damaged vascular bundles in the disc (acorn weevils often enter the acorn through these soft vascular bundles), (5) acorns with dark spots, and (6) acorns that have sprouted but the sprout is dead.

I like to collect acorns with two different sized containers: a 3-4 quart basket that I keep with me (see Blog header photo), and a larger 4-5 gallon sized bucket that I keep in a central location. This allows me to devote more time to picking up acorns, and less time to traveling back and forth to my bucket.

A properly dried acorn (left) and rapidly dried acorn (right)
Once the acorns are collected, it is important to dry them at a slow but deliberate rate. Drying acorns too quickly causes the nutmeat to turn black. While the black color of the heated acorns doesn’t initially cause any problems, my suspicion is that the heat drives the oil to the surface of the nutmeat where it may go rancid more quickly. Additionally, the thin brown covering between the acorn and the shell tends to stick to the acorn when they have been dried too quickly, whereas ordinarily, it sticks to the shell. At the opposite extreme, drying acorns too slowly is also detrimental. This is because acorns contain a lot of moisture when they are still alive. As they acorns begin to dry, they also die. If the remaining moisture lingers too long, the nuts will mold. Some species of acorns in some climates only require occasionally stirring in ambient conditions to dry properly, but our species and humid climate are not so forgiving. Until Garry Oak acorns are completely dry, they should never be left in a bag.

My homemade nut dehydrator
I think the easiest way to dry Garry Oak acorns is to spread them out one layer deep on baking sheets and place them next to a fireplace or forced air heat register. Rotate your trays occasionally and the acorns will dry in a couple weeks. My balanophagous friend Melissa from Oak Harbor recently told me about her success drying acorns in a food dehydrator. If possible, set the temperature of your food dehydrator to a low setting. With a little elbow grease and inexpensive materials you can manufacture your very own nut dehydrator out of a box, some hardware cloth or metal grating, and a small fan. Simply cut a hole in the side of your box near the bottom, suspend the hardware cloth horizontally above the hole, and dump your acorns into the box. The hardware cloth keeps the acorns from interfering with the fan as it forces air through the acorns. I got fancy and riveted together a box from sheet metal and used a partially disassembled thrift store hairdryer for my fan. The hairdryer is nice because I have the ability to blow hot air on the acorns. However, this particular hairdryer is a little too hot and blackens my acorns if left on “hot” for too long. I wish I had used one with variable temperature settings. The hair dryer is also noisy. CAUTION: If you make your own nut dehydrator with a hair dryer, I strongly recommend using fireproof materials and a GFCI outlet to power the hairdryer. It is probably also best to only use a home-made dehydrator in a fire safe area (like a concrete patio).

A Davebilt in action
Once dry the acorns shrink considerably in the shell and have a very hard texture, making them easy to shell. The best tool for shelling acorns is a Davebilt Nutcracker. These run about $150 and can be mail ordered from the small town manufacturer in California. If you are a serious acorn harvester, they are definitely worth every penny. The beauty of a Davebilt is that it operates on a continuous process (rather than a batch process) so you don’t have to stop until you are out of acorns. They work by squeezing the acorn between a wheel and a solid plate. You can adjust the distance between the wheel and the plate to accommodate different sized acorns (or other nuts). I have easily cracked 40 pounds of acorns in an hour! And most of the nutmeats come out as wholes or halves, which makes separating the shells from the nutmeats much easier. Other shelling methods (in ascending order of effectiveness) include the use of your jaws, conventional nutcrackers, and hammers, or better yet, Sam Thayer’s “towel method," which involves using a large piece of wood to crack rows of clustered acorns placed under a towel. Special mention will go to any 2 people that can pitch acorns at each other and get them to crack against each other mid-flight....

Separating the shells from the acorns is a time consuming process. There are many methods to speed up the chore including winnowing, floating, sieving, and shaking, which all rely on the fact that acorn nutmeat is more dense than the shells. Currently, my favorite method is to put the mixture of acorns and shells in a bucket (without water) and shake it back and forth vigorously. The lightweight shells slowly rise to the top and can be scooped off. I then sieve everything through ¼ hardware cloth in order to create two size categories that can be further winnowed and hand-sorted. The fines (which pass through the hardware cloth) are the most tedious to sort. If I have done a good job with the Davebilt, the bulk of the nutmeat will not pass through the sieve and the remaining large shell fragments are easily removed by hand. Though tedious for the eyes and hands, my nose gets a great deal of pleasure from separating acorns. They smell fantastic!

In order to enjoy acorns as food, they must first be leached to eliminate the bitter tannins. Tannins can be removed with hot water, cold water, or chemically (with wood ash, lye, or possibly ammonia). I will write about cold leaching, since that is how I process my acorns. Tannins are water soluble and relatively easy to remove with a little patience. The time it takes to leach tannins with cold water depends on the size of the acorn pieces. The Chinook living on the lower Columbia River buried whole acorns in artesian springs and left them to leach for an entire winter (for more information, read Bethany Mathews fantastic paper on the archaeology of acorn leaching pits on Sauvie Island published in Northwest Anthropologist 2009: Traditional Resources- Terrestrial). Native Americans in California take the opposite approach and pound their acorns into a very fine flour that leaches in less than an hour (albeit a different species). Someday I would like to try and leach whole acorns in an underground spring, but for now, I leach pulverized acorns. I put about 2 cups of acorns into a Vitamix Blender, add another 2 cups of water and then grind them (with earplugs on) for several minutes until I get a fine flour solution. I pour this slurry of acorn flour and water into a gallon sized glass jar, fill it the rest of the way with water, and then put the jar in the refrigerator or outside (if the weather is cool).

Acorn water after the first (left) and fifth (right) day leaching
Over the course of several hours, the acorn flour settles to the bottom and the tannins slowly dissolve into the water. Once a day I decant the tannin laden water (carefully pour it off the top of the settled acorns). Then I add fresh water and stir up the flour, and let it sit for another day. I repeat this process for 3-5 days, until the water nolonger has a reddish brown color and the acorn slurry doesn’t taste bitter. When it is done leaching, I pour off as much water as possible, and then use the product immediately, or store it damp in the refrigerator for up to 10 days.

Frying my Totally Tree Bread
A-Corn Bread ready to be eaten
Once my acorns are leached, I usually make one of two kinds of acorn bread. Totally Tree Bread is made with about 2 cups of wet acorn flour mixed with 1/4 cup maple syrup, spread out on a frying pan with some olive oil. Simply fry it on low heat for 30 minutes, flip it over, and fry it on the other side for another 30 minutes. You can make a savory version without maple syrup and a pinch of salt. Serve with mustard. Currently, my favorite is A-Corn Bread, which is basically a corn bread recipe that substitutes acorns for corn meal. I usually use about half wheat flour and half acorns. However you decide to cook acorns, be aware that the flavor of your dish is primarily determined by the thoroughness with which you have leached your acorns. Garry Oak acorns will always have a hint of bitterness, but properly leached acorns should primarily have a nice nutty flavor with a hint of molasses. Yum! I have some leaching now and I can't wait to eat them!

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  1. Do you have to dry the acorns while they are still in the shells? What would happen if you tried to dry them after removing them from the shell first?

    1. House Drying at Normal Room Temperatures: Allow the acorns to dry gradually inside your home at normal room temperatures. The acorns should only be one layer thick on the drying trays. If the acorns are relatively green, this drying method normally takes between two to four weeks.

  2. I have limited experience shelling and drying fresh acorns. The few times I have tried, I observed the nutmeat oxidizing to a light brown color and getting a fuzzy texture. I don't really know how bad the oxidation is for the acorn. Perhaps the nutmeat would dry more quickly out of the shell. My friend Melissa from Oak Harbor, WA shells her acorns fresh. Instead of drying them out of the shell, she goes on to leach them right away, and then dries out the leached acorn flour. I'd like to give her method a try one of these days.

    The main reason that I dry my acorns first is because they are easier to shell once they are dry. Fresh acorns have flexible shells and nutmeats that fill the shell up completely. As the acorns dry, the nutmeats shrink and the shells get more brittle, which makes them easier to remove.

    1. Hi Abe: Great blog! Melissa here! I use a traditional acorn stone mortar with a beach stone pestle which works great to smash the shells. (You can use a rounded depression in a big rock etc. I immediately dunk the shelled acorns in water which mostly prevents oxidation. I scrape off the thin, papery brown covering over the shells for that contains bitter tannins. Next I add a cup of water to my blender and then put 1-2 cups of acorns into my blender. The finer I blend them, the more surface area is available to leach out the bitter tannins quicker. I figured out a way to simulate a stream (one of the traditional leaching methods) by getting a large pot, put a mesh strainer with a handle that hangs over the edge of the pot into this...filling water until just the lowest portion of the strainer gets wet. I remove the strainer, put in a piece of muslin cloth and return this to the pot. Next I add 1-2 cups of finely chopped acorns carefully. Next, turn the faucet on to a very small, gentle flow, so that when the water hits the acorns, it doesn't disperse them out of the pot. The action of the fresh water on top encourages the acorns to release tannins faster and that water then flows over the edges of the pot, so the acorns are being 'flushed' continuously. (Since this does use a lot of water even if you do this for a short time you'll get a better release of tannins then just lest the acorns sit in water. When I let them sit in water (ONLY COLD WATER!) I pick a day that I will be home and then change the water throughout the day whenever I see it getting brown. I do this by pouring the acorns and water through the strainer with the muslin and then rinsing them with fresh water and returning them to a large Pyrex glass container with fresh water. The quart size canning jars also are nice to use also.

      When the water is almost clear to clear and the acorns no longer taste bitter I proceed I rinse them for another five minutes or so using my 'homemade stream' method. After this I dry these a bit using a flat dish cloth and spread them onto my food dehydrator non-stick sheets. (You can also use an oven at very low temp as you don't want to 'cook' them but simply 'dry' them. I monitor the drying process every hours or so and rotate trays to keep things more uniform re. drying. Once dry, I put the nutmeats into my larger food processor to grind into finer acorn flour. I freeze this in triple bagged freezer bags. This way, they keep their freshness longer. I tried boiling acorns and do NOT recommend this. The full, rich, "Grape Nutty' flavor is lost through boiling. The flour keeps in my freezer for a year. I make acorn cookies using the Quaker Oats 'oatmeal cookie' recipe and just substitute 1/2 of regular flour for acorn flour. Beware, when I have used whole wheat flour, and gluten free flour there is a lot of crumbling that has happened in my baked goods. I like making a bread that has walnut oil, maple syrup and is my three tree bread secret recipe!

  3. How often do you eat acorns? They seem to have great potential as a staple food...

  4. I leach about 2-3 batches of acorns a month, which usually yields enough leached acorn flour for us to include acorns in 6-10 meals a month.

    I just shelled 2 gallons of Canyon Live Oak acorns and I can' wait to have my first taste of this species.

  5. Nice website!

    I love acorns and recently found out of a great and super fast way to cold leach acorns.

    After using your Vita-Mix or blender to pulverize into flour, add the wet mixture to a women's stocking with one end tied. Rinse under the kitchen faucet with cold water until you start noticing the color change and then begin taste testing until the tannin has been fully leached. Within a few minutes, you can get rid of most, if not all, of the tannin astringent taste. Quite an efficient method and it sure beats the waiting for your glass jars to do the work for you or even Sam Thayer's homemade leaching contraption.

    For more info and a video of the process, you can check out a youtube video on the method:


  6. Hey there fellow Acorn Eaters!
    I like the leaching jar method since you can also collect the starch and the oil and it uses much less water. When I'm in a hurry I do use the knee-high method.

    Has anyone tried letting their acorns sprout before processing. I've heard the end product is sweeter.
    Best wishes,

  7. I just bought this acorn gatherer tool.

    We've used it already and it works great. However the acorns are in their 1st phase and are no good so we're picking them up and burning them in the fire. Looking forward to oct/nov to get the better batches and see how it goes. Thanks for this article!

  8. I have just started the jar leaching process today with my Valley Oak acorns and would like to dry my flour and store it to make a pie crust for thanksgiving. What would be the best method for drying out my flour? And also for storing it once it's dried?

    1. Hi Jessica,
      I spread my wet acorn flour on a baking sheet and put it in a food dehydrator. You can use an oven on the lowest heat setting possible. After it is totally dry and crumbly, put it in a blender to break up the chunks and make a nice flour that stores well at room temperature in a sealed container.

  9. That's awesome!
    Can't wait to try it out myself.

    Regards Julius

  10. Hi glad everyone is interested in our own westcoast oak, Quercus garryana.
    Before you harvest for your personal consumption, remember the future of our oak lineage.
    Those acorns you are now harvesting, are a legacy from the past.
    Plant as you reap,so more oak habitat is shared.
    I love oaks, they have shared with us and supported our civilizations.
    Where oaks have grown,man has harvested, farmed, and developed.
    Now, globally, little remains of the great oak savannahs, woodlands, and forests.
    The goldrush is over. Now, is the century to love the earth.
    Restore what man has taken, replant the oaks.

    1. Well said! Here is Oak Harbor there is about a 95% natural germination rate. Oaks here literally 're-seed themselves' every opportunity they get. It's very easy to grow local oaks. If you want to 'grow your own' I suggest a long, narrow 'tree pot' to allow the taproot to grow nice and long the first year.

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  13. Great information -- thank you! Do you know if I can harvest acorns off the tree while still green but almost mature? And then let them finish ripening at home? The pressure from the animals where we live means no acorns for us if we wait until they have fallen...

    1. If the animals are eating acorns, that means they are staying out of your garbage cans. Let the animals eat.

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  14. I have picked acorns from English Oak with good success. They likely have more moisture so be sure not to let them mold. What species are you after?

  15. I am new to Vancouver Island, is there a place near Nanaimo to gather acorns?

  16. I am new to Vancouver Island, is there a place near Nanaimo to gather acorns?

  17. If I'm able to shell my acorns easily without drying them (Tanoak), then can I just leach them even though the nutmeat still has moisture and then cook with them right away without ever drying them? Thanks!

    1. Hi Julie, a friend of mine commonly cracks and leaches fresh Garry Oak acorns, so I think it is reasonable to expect that this would work for Tanoak as well. However, I find that fresh acorns oxidize quickly when they nut meat is broken during the shelling process. It probably isn't a big deal, but I don't like the way the oxidized nutmeat looks.
      Best of luck!

    2. Abe, just have a dish of water to immediately dunk them into after you shell them and this mostly prevents oxidation if you do it within a minute or two of shelling.

  18. Interesting stuff. I am going to try the "cornbread", but actually prepare it more like polenta with a sauce.

  19. I'm in So. Cal and we are on our first batch of acorn flour....I've been cold leaching them overnight for a week and it seems like they are STILL a bit tannic! Have also saved the acorn fat/protein to re-incorporate back in with them. Any suggestions on how long this may take? I believe the tree is a Quercus agrifolia variety - that is the one that is most like ours (pointy acorns, thorny leaves in a smaller size, etc) and it seems like they are BITTER!! Hopeful, but ....this is taking forever!

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  21. Much appreciated! I am going to try this with English Oak Q.robus and see how well the end product turns out. I have lots of English Oak so I hope that they are usable.