How to Make Acorn Flour

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Acorn flour is one of the most practical (and versatile) wild foraged flours available.  Processing acorns into flour takes patience and work, but it’s downright delicious.

This past fall I set out to harvest as many acorns as possible, with the goal of making at least a dozen different acorn based recipes.  Almost all of those recipes start with grinding and leaching the acorns into acorn flour.

Acorns contain natural tannins that must be leached from the nutmeats before they can be eaten, and the fastest way to remove the tannins is to create as much surface area as possible. 

That means grinding the acorns into flour first, even if you’re not planning on making baked goods or acorn bread.

There are a number of ways to make acorn flour, and many different methods were used historically.  Some involved using wood ash to bind the tannins, others leached the acorns whole in water-filled pits for months at a time, and still, other methods boil the acorns for hours on end.

Each of these methods has it’s pros and cons, and some manage to alter the flavor of the acorns and/or the structure of the starch within the nut (for better or worse).

Coldwater leaching is my preferred method, and it’s incredibly simple.  It leaves you with the most versatile end product, with all the natural binding starches intact (for better bread) as well as the best flavor.

With the cold leach method, the starches within the acorn maintain their binding properties, and while there’s no gluten, it’ll still hold together well enough for pancakes, cookies, cakes, and even acorn pasta…

The cold leach method also happens to be the least labor-intensive method, requiring minimal work beyond patience (and acorn cracking). 

(The only catch is, this method assumes you have plenty of fresh water available.  In Vermont, we’re rather water-rich, but this may not be the best method for arid climates.)

How to Make Acorn Flour

The whole process starts with gathering the acorns.  On a small scale, you can simply pick up acorns off the forest floor in the autumn.  In urban and suburban environments, city parks are a good source, and you’d be amazed at how many public buildings landscape with oak trees.

Out here in the woods, it’s easy enough to rake them up by the bucketload.  

(There is one commercial acorn flour manufacturer in Greece, and their founder wrote a book about their process titled Eating Acorns: A Field Guide.  They place nets under the trees to gather the acorns more efficiently, and to prevent acorn weevils from infesting them before they’re gathered.)

Choosing Acorns to Harvest

There’s a myth that white acorns contain fewer tannins, which isn’t universally true.  Some studies even show that some species of white acorns may have more tannins, but they’re just more tightly bound within the nutmeat and harder to leach properly. 

White or red, it really doesn’t matter. 

The best acorns to harvest are those that you can gather in quantity because you’re going to need at least a few gallons of nuts to make a meaningful amount of flour.

Cracking Acorns for Flour

Cracking acorns is where the real work starts.  While you can rake up a bucket load of acorns in a few minutes, plan on spending hours cracking them.  (If you’re doing it by hand.)

Historically, this would have been done by placing the acorn on a hard surface (like a rock) and then hammering it with another rock.

Setup at my kitchen table on a rainy fall evening, a cutting board and hammer works pretty well.

Through a lot of experimentation, I found that placing the acorn right side up (pointy end down) allows the point to dig into the cutting board when struck.  That prevents the acorn from skidding out to the side, and ensure’s it cracks with one sharp blow.

(It’ll make a divot in your cutting board, so use one you don’t mind marking, and then that divot conveniently holds each of the rest as you crack them.)

Figure out what works best for you, as you’re going to be here a while.

As you work, watch out for acorns with a hole in them.  These acorns are no good, and have already been consumed by acorn weevils.

If you’re really adventurous, Pascal Baudar has recipes for protein-rich acorn weevils in his foraging book New Wildcrafted Cuisine.

So if your goal is “survival protein,” you can process these, otherwise, toss to the chickens and keep looking for clean acorns for flour.

Once cracked, the nuts are a lot more compact than they were in the shell.

I kept careful notes on yields…which I’ve since managed to lose.  So a rough estimate, they’ll lose about 1/3 of their total volume in the cracking process.

Grinding Acorns for Flour

Once you’re done cracking, it’s time to grind the nutmeats into flour.

This is a lot easier than cracking, especially if you’re willing to use a food processor or blender for the job.  (Lacking that, you can pound them with rocks.)

Regardless of your grinding method, sift the flour out periodically as you work.  You’ll be left with fine flour, as well as some larger “acorn grits” that you can either continue grinding or leach as is.

Leaching Acorn Tannins

Once ground, leaching acorn flour takes days of patience.  It’s hands-off time, for the most part, all you’ll need to do is change the water every 12 hours or so.

Fill a container about 1/3 to 1/2 way with ground acorn flour.  Fill the rest of the way with cool water, give it a shake, and then set it in some out of the way place (pantry, etc).

After about 6-12 hours, carefully pour the water off without disturbing the acorn flour settled at the bottom.  Refill the container with clean water again and wait.

After about 2-3 days, you can begin tasting pinches of the acorn flour.  When it’d ready, it’ll taste ever so slightly sweet with no hint of tannins.

If there’s even the tiniest taste of tannins in the flour, allow it to leach for more time.  A hint in a tiny pinch means an inedible baked good once you’ve used cups of the stuff.  This is important, make sure it doesn’t have any tannin taste.

Depending on the acorns, this process can take as long as 7-10 days with water changes every 12 hours.

Drying Acorn Flour

Once you’ve leached the tannins from the acorn flour, it needs to be dried for storage and most uses.

Pour the flour through a piece of very fine mesh cheesecloth (90 grade) or something similar like an old (but clean) cotton t-shirt.

The resulting wet mass of “flour” can be used as-is in recipes, provided you reduce the rest of the liquid in the recipe slightly.  It won’t keep long this way though and needs to be stored in the refrigerator.

Wet acorn flour has plenty of starch, and will bind together quite well after the cold process.  

Storing Acorn Flour

Wet acorn flour will only last a week at best in the refrigerator, but it can be dried for long term storage.

I spread it on silicone sheets in my dehydrator, but you can also spread it out on trays in the sun for a more passive method.  It’ll need to be stirred/turned every few hours to ensure it dries completely.

Once it’s completely dry, acorn flour will store a few months in the pantry (or a bit longer sealed in the fridge).

Keep in mind that acorn flour is a nut flour, similar to almond flour in some ways.  It has healthy fats that add to its nutritional value, but can also go rancid over time.

It’s best for work in small batches, only processing as many acorns as you’ll eat in a month or two, and storing the rest of your harvest in the shell.  As with most nuts, in the shell will keep quite well, and last much longer than processed acorn flour. 

Cooking with Acorn Flour

Adapting white flour recipes to acorn flour can be a bit tricky, as it’s gluten-free flour.  Instead, I’d suggest looking for recipes that include almond flour and make a 1:1 substitution.  

Acorn flour also substitutes well for cornmeal.

It works wonderfully in cakes, pancakes, cookies, and quick bread (like banana bread). 

The one thing it won’t do?  Make a fluffy yeast-risen sandwich bread.  Without gluten for structure, acorn flour just can’t hold up to yeast leavening. 

(That said, if you’re desperate for an acorn flour sandwich bread, it’s technically possible.  If you’re willing to add xantham gum and all manner of other stuff that’s put in gluten-free bread, you might get something that’s almost fluffy and technically edible.  It’d be a crime against the acorns in my book, but it’s your choice.)     

We’ve used acorns to make all manner of things, from acorn pasta and cake, to acorn nut butter, ice cream, coffee, and more.  I’m slowly getting the recipes for all that tastiness posted.

In the meantime, check out this article for more than 60 Acorn Recipes from around the world, with traditional preparations from Asia to Spain, the Middle East, and the Americas.

Other Acorn Flour By-Products

As a side note, this process yields more than just acorn flour.  If you separate out the coarse ground acorn bits, you’ll end up with tasty acorn grits.

They still need to be leached, just like the fully ground flour, so follow the same process.

Acorn grits cook up just like oatmeal, with just a quick simmer in water, and they make a delicious hot breakfast cereal with a bit of maple syrup.

Beyond that, if you choose, you can separate out the very fine acorn starch.  It’s the last to settle when you shake the water filled jars, so it’s easy to find at the top of a jar during the leaching process. 

I leave it in the finished flour, but it’s traditionally used in Asian cooking.  There are actually commercial acorn processing plants in Korea that make and package acorn starch for sale.

It’s used to make an acorn jelly known as dotori-muk, which is then cooked like tofu.

Acorn starch is also made into traditional noodles in place of other gluten-free starches, like rice starch.

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