Developing a process by which to turn the bitter nut of the oak tree into a viable and nutritious food staple was one of the greater innovations of mankind. Early Homo sapiens recognized the potential of a tree that produced nuts in massive quantities, were easy to crack and shell, and easily stored for long periods of time. Rendering acorns edible allowed humans to subsist over barren winters and conquer new lands where food sources would have otherwise been uncertain.
Long before the primitive grain that would one day be called maize made its way from South American tribes to the farms of indigenous North America, it was the simple yet ubiquitous fruit of the oak tree that provided the natives of this continent a staple food source from which to live and thrive. Before any European or African set foot on this continent, before America ever knew the likes of horses or metal, the inhabitants of this continent were “paleo” before paleo was cool.
Though there are some places in the world where the acorn is still eaten as a sort of novelty, it has all but fallen out of grace with the pallet of modern man.
Why so bitter?
For ancient humans, this seemingly perfect food had but one caveat — tannic acid. This substance is not only extremely bitter tasting to humans, but also toxic in high doses. Even in lesser amounts, it can cause nausea and digestive distress. This is the same substance found in many foods such as the skins of wine grapes and is referred to as tannin. If you follow the path of your ancestors and learn how to remove the tannins from acorns, you will find that this bitter little nut can become quite edible.
Here in Southern Indiana, acorns start falling in mid-late September and continue through early November, depending on species and environmental factors. I collect acorns from a variety of species, some large, some small, some red, some white. I rarely differentiate them in the field, as they will all require processing. I may separate red group and white group acorns if I have a substantial number of either or both. Mostly, if I separate acorns at all, I separate them by size. If you are getting your acorns from a few trees of the same variety, this is not an issue. However, if you are like me and gather acorns from a great variety of oaks from multiple locations, this can become important.
In North America there are roughly 60 species of oaks that are native to the United States and still many more that have been intentionally imported or accidentally naturalized from Europe and Asia. The specific identification of each of these individual species is far beyond the scope of this article, just note that all are edible after processing. Therefore, let us keep to the two main subgroups of oaks that are prevalent in North America, red oaks and white oaks.
All oak leaves are lobed, but the lobes of the red oak leaves tend to be much sharper and more pronounced. The margins of white oak leaves tend to be lobed in a much more rounded fashion, producing a bit of a scalloped appearance. Red oak leaf lobes also end in bristles, which can be inconspicuous at first glance. The acorns produced by each group have some distinctions as well. Acorns of the white oak produce caps that are bristled, while red oak caps have scales. Red oak acorns tend to be more round and squat, while white oak nuts are often oblong and somewhat football shaped. Both can vary in size from the size of a chickpea to a little less than a golf ball.
One particular reason you might want to differentiate the two groups is their seasonal viability. Both types produce acorns in the fall, but red oak acorns do not begin to sprout until the following spring and can be gathered late into winter if they have not already been taken by animals. White oak acorns, on the other hand, begin their life cycle as soon as they fall, sprouting and sending down roots within a week of falling from the tree, shortening the harvest season substantially.
Like all crops, acorns can succumb to pests. Now that you know how to differentiate oak groups, you will need to know how to differentiate viable acorns from bad ones. The most common infestation of the acorn crop is the acorn weevil. These little pests are the larvae of insects in the Conotrachelus and Curculio genera. The females of these insects bore small holes in the immature nuts where they lay their eggs. When the eggs hatch, the grublike larvae feed on the nut inside, which destroys it. Many of the acorns that you might gather will be infested with the weevils, so it is worthwhile to know how to tell if an acorn is affected before you collect it or start processing it, so that you don’t waste time and energy on worthless acorns. The process of segregating good and bad acorns is twofold.
In the field, you can tell if a nut is infested with a weevil by a few distinguishing features. First of all, if an acorn has fallen from a tree but is still attached to its cap, that acorn is probably infested with an acorn weevil. There will be exceptions to this, but so few that it is not worth gathering acorns with caps attached. Also, the round disclike section at the back of the acorn where the cap was previously attached should be perfectly intact with an uninterrupted margin. If the edge of it is damaged, broken, or discolored, the acorn will be bad. Any acorn with this section being convex, bulging out, or disrupted should also be discarded. Essentially, any acorn that is not perfectly intact will be, to some degree, infested. Any nut you find that has a visible hole in the hull will certainly be bad. This is where the weevil made its exit from the acorn and left behind only a shell full of its excrement.
So, all of the acorns you’ve gathered look good and fresh and the rear disks are complete and uninterrupted. Inevitably, some of these will still be bad. There is a quick and easy way to tell which acorns you’ve collected will be good and which ones will be bad. Place them in a bucket of water. Any acorn that floats is bad. Make sure you stir them around really well so that any would-be floaters that may be trapped under other nuts have a chance to get to the surface. Most of those that sink will be good, though you will certainly still find a few bad ones in the shelling process. Still, between examining them in the field and the float test, you will have eliminated nearly all of the bad ones.
The nutmeats of fresh acorns are affixed to the flexible hull by a thin membrane. When acorns dry, the shell becomes more brittle and the nutmeat shrinks slightly, detaching it from the hull and making it easier to crack. They can be dried by spreading them one acorn deep on baking sheets or other containers, and storing them for a few weeks in a warm place. The amount of time required will change depending on the size and species of your acorns and the temperature of the space. Setting them near your furnace or woodstove will speed the process. You could also employ a food dehydrator and cut the dry time significantly. Fully drying the nuts will allow them to be stored for long periods of time, months, or even years at room temperature. By drying, you can gather large quantities of acorns in the fall and process them throughout the winter months when not much else is in season. It is my personal preference to shell them somewhat fresh, when possible. I will bring home a couple gallons of acorns every few days and — after the float test — store them in the refrigerator for 24 to 48 hours. The nutmeats will just start to detach from the hulls and can be easily cracked with a mortar and pestle.
Acorn shells are thin and easy to remove compared to other nuts like black walnuts or hickory nuts. If you’re gathering for fun and don’t have a large amount of acorns to shell, a mortar and pestle works quite well for cracking. Give each nut a good whack with the pestle, and they’ll usually crack on the first impact. If the nut is standing upright so that the pestle hits it directly on the nipple, it will usually crack right down the center, allowing you to extract the nut whole or in uniform halves in most cases. If you’re harvesting acorns on a larger scale, you’ll have to speed up the process. Unless you want to invest some money in a commercial-grade nutcracker, spread fully dried nuts out onto an old towel and stomp them with your shoes. My kids and I have a lot of fun with this part of the process, for obvious reasons. You can also use a length of lumber such as a 2-by-4 as your cracking instrument. Once the shells are cracked the nutmeats will then typically come right out of the shells with minimal effort. A nutpick will easily separate what your fingers cannot. My daughters and I will sit around a bucket of acorns cracking and shelling them together, chatting the way my mom and my aunties would do while sitting around snapping green beans and shucking corn. It takes time, but it’s worth it and great memories are made in the process.
As previously mentioned, the tannic acid content of acorns is the only thing standing in the way of them being edible. Fortunately, the tannic acid that causes the bitter flavor is water soluble, which means that they can be removed by water through a process called leaching, of which there are two methods: hot leaching and cold leaching.
Hot leaching is substantially easier and much faster. This method is basically just boiling the shelled acorns in several changes of water until the bitterness is gone. How long they will need to be boiled and the number of water changes required will depend on the species, size and number of acorns in your batch. You’ll just have to keep tasting them until the bitterness is gone, usually a couple of hours with three to six water changes. Once you are satisfied with the flavor, air-dry the nuts in a warm place or in a dehydrator and then grind them into flour. A coffee grinder works excellently for this. Though the hot leach method is quick and easy, it comes at a price. The boiling process not only extracts the tannic acid, but also a lot of the starches. The result is that the flour will not bind to itself when cooking so it must be mixed with other types of flour. Hot leaching also diminishes the nutritive qualities of the acorn substantially.
Cold leaching, on the other hand, will retain both the nutrients and the starches, but it does require more work. Start this process by filling a blender about half full with your shelled nutmeats and filling it nearly the rest of the way with water. Puree in a blender until the mixture is about the consistency of a gritty milkshake. Then pour the mixture into a container with as much water as it can hold, cover, and place in the fridge. The acorn nutmeat will settle to the bottom, and the water soluble tannins will leach out into the water and rise to the top. Pour off the water and refill twice a day for one to two weeks. Then taste a teaspoonful to gauge the bitterness. If they are still bitter, refill the water and let them continue leaching, tasting them every few days. Due to the variations in species, climate and other factors, this is the only way to tell if they are properly leeched.
You can reduce the time needed to leach by increasing the volume of water while maintaining the volume of acorn meal. For example, if I leach 3 cups of red acorn meal in 1 gallon of water, it will take a month and over 25 water changes to properly leach. Whereas 3 cups of acorn meal in a 10-gallon cooler will leach in one week with half the water changes.
Once the bitterness is gone, you can squeeze out the water through a cheesecloth or old T-shirt material, and you'll have a starchy, sticky dough ball you can use to cook right away like course, wet flour that doesn't rise. I prefer to dry it in my dehydrator and grind it finely in a coffee grinder and store the flour in the pantry. The drying process will darken it to a rich brown color that will lend an earthy color to your recipes.
Cold leached acorn flour can be used in just about any recipe that calls for nut flour, so even if you’re not a paleo dieter, having a paleo cookbook or two on hand is a good idea. I urge you to think both inside and outside of the box of Western cuisine when preparing your acorns for meals. Experiment with tried and true recipes, incorporate acorn flour in your pancakes or catfish breading and homemade pasta. Roast large pieces of hot leached acorns and add them to stew or gumbo. Get creative and use cold leached acorn flour for Indian naan, pizza crusts, or wherever else your imagination takes you.
Seven nut recipes for every country kitchen.
Clyde Myers lives in southern Indiana with his wife, Amy. He is a foraging instructor and enjoys writing about wild foods.