Did someone dare you to eat an acorn when you were a kid? Yeah? Me, too. And I'm sure you spat it out in disgust, as well. It might have been your first strong experience of astringency, the quality in food that makes you pucker and your tongue feel fuzzy with near-electric bitterness. Astringency likely has a lot to do with why acorns have fallen out of favor as a food for humans. That hasn't always been the case. Many cultures have utilized acorns throughout the ages, including some of the first people to inhabit California. Even today, circular depressions can be found in the rocks there, evidence of acorn processing.
Here's the thing you need to know as a modern forager - processing acorns takes time. But it is dead simple, and you need only let your taste buds guide the process. Astringency in acorns is caused by the same compound that makes tea pleasantly astringent, tannins. Tannins are water-soluble, so they are easily removed from acorns by a process of exposing the nuts to water, letting it sit, dumping it out, then repeating as necessary until the acorns no longer taste astringent. This process is called leaching.
You can leach acorns with either hot or cold water. Using the hot water method, you simmer acorns on the stovetop in a good amount of water, change the water, boil again, and keep up the water changes until the acorns are left without astringency. The main objection I have to using this method is that it has been my experience that it leaves the acorns less flavorful. The acorns smell really delicious while they are boiling, but that aroma/taste seems to get dumped away with each successive change of the water. The second problem I have with hot water leaching is that I find it tedious to babysit boiling water. However, many people use and enjoy this method, so don't let my objections stop you. Apparently, if you are hot leaching your acorns, you can keep them whole. I've not tried this, but it could certainly be nice if you wanted to use them as bigger pieces when cooking.
After many years of experimentation, I now leach acorns with cold water all the time. Let me back up, though, by saying that whether you hot or cold-leach your acorns, you must first crack them. Once the thin shells have dried enough to become brittle (you can do this in a cool room in an arid environment, or with a very low oven or dehydrator), this is fairly easy compared to picking something like black walnut meats. You can use a nutcracker, or you can place them between two towels and whack them with something solid.
Once your acorns are free of their shells, they need to be evenly ground before they can be cold-leached. I use a grain mill for this purpose, first running them through the burs to get chunks, then processing them a second time to get meal. Some people also use their Vitamix. If acorns get completely dried before they are ground, they can be hard as rocks, so be careful with whatever equipment you use for grinding them up. I tend to grind mine when they are relatively fresh, in part to avoid the crazy-hardness problem.
The next step is to put your ground acorns into a vessel with cold water. Traditionally, this was done in a cold running river. I don't have access to a clean one of those, and I'm too leery of the oft-recommended method of putting them in your toilet tank. So, I use gallon jars. I fill the jars between 1/6 - 1/5 full with ground acorns, then fill them to the top with cold water. You can use larger containers, but they get heavy, and if the acorns start to ferment (you should be changing the water often enough that this doesn't happen) and you need to get them into the fridge, larger leaching containers can be inconvenient. Once the acorn and water are in the jar, I usually use a chopstick to stir them up. Then, I just leave them sitting in a cool place until I'm ready to change the water. The water should be changed at least twice per day. But if I'm home and I see that the acorns have settled into a layer of sandy-looking meal and a layer of starch on top so that the water above is no longer cloudy, I go ahead and change the water. Just decant the water straight off the top, being careful not to pour out the layer of starch, because that is what adds a stickiness to your acorn flour that makes it more versatile in baking. Keep changing and refilling the water until your acorn meal no longer tastes astringent. How long this takes varies greatly. I've had a few batches that have taken weeks. Most of the time, it takes at least four days. Just let your tongue tell you when the acorns are ready.
Once the acorn meal has been leached of astringency, it's time to drain and squeeze out the water. I may be the only one, but I find cheesecloth to be useless for this sort of thing. Instead, I've become quite fond of using cotton flour-sack towels, the kind you can get in a 5-pack for $5 at Target, for any project that requires draining or straining. The towels end up getting really stained, but I've yet to wear one out. Line a colander or large sieve with a towel, then pour the acorns and the last of the water into the towel. Pick up the corners of the towel and gather them in your hand. Start to twist the excess towel so that it forces out the water and makes the remaining acorn meal into a ball. Use your hand to squeeze out as much excess water as you can. I find this is easiest if I crank on the excess towel with one hand, keep the acorn mash in more of a bun-shape than a ball-shape, and squeeze around the edges of the "bun" with my other hand. This is the part of acorn processing that always leaves me sore. It takes some muscle power. When you get down to the last bits of water, save what you are squeezing out. This water contains acorn starch, and can be lightly sweetened and heated and enjoyed as nut milk (thanks to Sam Thayer for that tip).
When I can squeeze no more, I unwrap the acorn bun/ball from the towel and dump it onto a silicone or parchment-lined dehydrator tray. I used to do with on baking sheets, and let the meal sit around for a few days to dry, but I live in an arid environment where it's hard to make anything mold, so I imagine most will have to use a dehydrator or oven (I've no experience with the oven method). This is the part of the process where I find a butter knife to be really useful. I use the butter knife to scrape all the excess acorn from the inside of the towel. Then, I use the butter knife to chop and fluff the acorn meal as it spreads out on the tray. The acorn gets really compacted in the process of being squeezed dry of water, so chopping at it helps to create non-squished sandy acorn, which dries more evenly. I've found that the amount of acorn I leach in a gallon jar fits nicely onto one square Excalibur tray. I dry the acorn meal for about 24 hours at 125˚.
The final step I take is to run the dried acorn meal through an electric food mill to make it as fine as flour. This isn't totally necessary, and it will depend upon how you intend to use it. If you are making a cookie-style pie crust or acorn polenta, the slightly courser texture is nice. But for baking breads and cakes, I like the acorn flour to be fine. If you are lucky enough to have processed large quantities of acorn flour to this point, it should be stored in the freezer.
Here's where I'm going to throw in one confusing bone. This year, I've been roasting all of my acorns in the shell as soon as they are harvested. I roast them in a single layer on a baking sheet for an hour at 250˚ (F). I then shell, grind, and leach them. I like the rich flavor this adds to my acorns. Also, I suspect, but don't have any solid proof, that it decreases the time that acorns need to be leached.
Sounds all good, right? For the most part, yes. But if you were to make acorns the staple of your diet, this might be a bad idea. There's a lot of debate about the subject of tannins in acorns and whether or not they should be leached (no joke, this is a push-button topic in the world or foraging). There are some people out there who have access to "sweet" acorns that don't taste tannic, and they enjoy them without leaching. It wold seem, though, that all acorns contain tannins, whether or not they can be tasted (Thayer, Wild Food Notebook, Nov. 2013).
Regardless of how you fall on the tannin-leaching fence, according to to Arthur Haines, there is another reason to leach your acorns. Leaching also breaks down phytic acid, which is a sort of anti-nutrient that can steal minerals from your body. In traditional cultures, grains, beans, and nuts were leached in this manner to make them more digestible. This brings me back to my pre-roasted acorns. According to Haines, roasting reduces the enzyme phytase, which is what breaks down the nutrient-stealer phytic acid when you are leaching acorns. So, if you decided that you wanted to make acorns a cornerstone of your diet, pre-roasted the acorns would probably be ill-advised. I harvested a lot of acorns this year, but I still don't eat enough of them for this to be a big worry for me.
If you have more questions about harvesting or processing acorns, I would recommend that you read Sam Thayer's chapter about acorns in Nature's Garden. It is a very thorough chapter, and where I first learned about dealing with acorns. This article by Green Deane also has a lot of interesting tidbits.
So, after some work, you've got acorn flour on your hands. Whatcha gonna cook? An easy place to start is to substitute acorn flour for 1/4- 1/3 of the normal flour in some of your favorite baking recipes like cornbread or cookies. You might also want to make Hank Shaw's tortilla-like acorn flatbreads. I've made all sorts of goofy things with acorns in the past, including acorn frangipane (it's like the famous almond paste). This year, with a real abundance of acorns on hand for the first time, I've had enough to flour to play with some more unusual recipes, especially savory ones. I've got acorn polenta and acorn tamales coming up in future posts. For now, I want to show you the easiest and tastiest thing I've made with acorns so far this year. I've happily served it in my house more than half a dozen times so far this fall.
1 c. acorn flour
1 c. old-fashioned oatmeal
1 tsp. salt
2 tsp. ground cumin
1/2 tsp. ground coriander
1 tsp. baking powder
1 tsp. onion powder
2 cloves garlic, minced
1/2 c. loosely packed parsley, chopped
2 Tbsp. olive oil
1 c. warm water
1. Mix all of the dry ingredients together in a medium bowl, then stir in the garlic and parsley.
2. Make a well in the center of the dry ingredients, pour the olive oil and eggs into the well, then gently whisk them with a fork before stirring them into the dry ingredients.
3. Stir in the water. Make certain all of the ingredients are thoroughly combined. Cover, and let sit for 30 min.
4. Break off a tiny ball of the dough, roll it into a ball, then squeeze it with your fingers. It should stick together quite well without being wet. If the ball crumbles when you squeeze it, add more water a tablespoon at a time until it will hold together. If the ball seems sticky, stir in a bit more acorn flour.
5. Form the dough into tiny patties like hamburgers.
6. Cover the bottom of a medium skillet with cooking fat or oil. You want enough oil so that the acorn falafel patties will brown on the bottom and a little bit up the sides. Bring the skillet up to medium heat.
7. Cook the acorn falafel patties in the hot pan on each side until they are brown. This should take about 5 minutes per side. You want the egg to cook through, and for the patties to get crispy, but you don't want them to dry out or burn.
8. Serve the acorn falafel stuffed into pita bread, along with some cucumber-yogurt or tahini sauce, as well as some extra lettuce or cucumbers.