A while ago I stayed with my boyfriend and his family in the 'burbs and I had some time to kill. Luckily, he lives on the perfect road:
I prefer foraging in the woods but there was something really methodic and relaxing about picking up piles of acorns from under the trees in the neighborhood. I probably got some funny looks from the neighbors but I didn't really notice if I did.
Acorns have been used for thousands of years as a food source and have gone from prized food to "poor man's bread" in that time. This is a great post about the history of acorn use, plus a recipe for acorn cake. The Native Americans in this country used acorns for flat cakes and breads and as a thickener for stews, among other uses. Today, the culture that seems to use the most acorn products is actually Korea. It makes sense, since oak trees can grow all over the world.
Another interesting thing about oak trees is that they don't have the same yields every year. They actually go through cycles every few years, so it's good to know where a few trees are to check each fall. Some of the trees I came across were pretty bare while others (like the branch pictured above) were practically dripping with acorns.
I harvested a bunch of acorns in Idaho but when I moved to Eugene, Oregon I decided I wanted more. Luckily there are plenty to go around in this town too!
But wait, you can eat acorns?
Yes, yes you can. But it takes some work. A LOT of work. Though it varies immensely depending on species, most acorns contain a fair amount of tannins. These aren't anything to be particularly afraid of- they're what give many wines some flavor, for example. But in large doses they aren't great for you and can cause some serious stomach upset. I think it'd be hard to eat that many, though, as tannins are bitter and astringent and make your mouth feel like cotton. Not the most appetizing. Acorns have to be leached in order to remove the tannins to make them both safe and palatable. See below.
I learned a lot of what I know about processing and harvesting acorns from this post. Don't pick acorns directly from the tree. Instead, pick up the ones on the ground below that have fallen off. Check them for holes and scratches and discard any that the squirrels or bugs have already gotten to. It's okay to harvest slightly-green acorns, as long as they separate easily from their caps. Once you've gathered as much as you want to, lay them out somewhere safe and sunny to dry for a few more days. The green acorns should ripen in this time. Beware of bugs, though, sometimes acorns are a home to insects that can emerge and get into your home. Many acorns contain small grubs. I'm not particularly concerned about this- I just figure it's extra protein. But if you are, you can fill a bowl of water and put your acorns in it. The ones that float are likely to have grubs in them, munching away at the nutmeats. The ones that sink should be more intact. You'll have to dry the acorns out again after using this method of testing, if you do.
As an extra precaution, I roasted my acorns at the lowest possible setting in my oven for a couple of hours, just to make sure they were totally dried out and wouldn't mold while I stored them for a few weeks. The smell they emitted while cooking in the oven was intoxicating- malty and roasty and delicious.
Once they were roasted and had cooled enough to handle, it was time to process. This is laborious and time-consuming, so it's best to have some friends over and drink some wine and make it into a party! I made my minions help with the tedious parts. We started by shelling the acorns. You can use pliers or nutcrackers to break them open, but we found that gently hitting them with a hammer and then doing the rest by hand was pretty easy. The shells aren't super thick.
As you shell the acorns, place the nutmeats into cool water. They oxidize quickly and will turn a darker brown if exposed to air for too long. It doesn't harm the acorns, but it makes them less pretty. (Think of browning apples, for example.)
The next step is to leach the tannins out. Since I'll be using this batch of acorns to make flour for baking with, I decided to use the cold-water leaching process because it leaves more of the starches intact and also supposedly preserves the flavor better. The downside is that it takes a LOT longer than the hot water method (see below.) I used a meat grinder to grind my acorns into fine chunks, then placed them into glass containers and topped with water. Then I stuck those in the fridge and let the tannins leach into the water overnight. I kept them in my fridge and changed out the water a couple of times a day (I just carefully poured it off the top and re-filled, then stirred.) After a week the nuts were much more palatable, though still noticeably bitter. It ended up taking about two and a half weeks before they were bland enough that I was satisfied. Whew! It was a LOT of work changing out that much water a couple times a day for weeks. The only way to know they are done is to sample them. Just chew a little piece and if it tastes bitter and astringent, you should keep going. Don't just let them sit in water in your fridge, though- it is important to change the water out often or else they will start fermenting or molding!
Once they are properly leached, I placed the soggy meal into a fabric bag to strain, and then dehydrated it overnight at a low heat to dry it out. Then we used my coffee/herb grinder to grind the meal into flour and sifted it to be sure we had a consistent flour.
Since I had a lot of leftover acorns I decided to have another minion night to try the hot-leaching method which is a lot faster. It takes a little more of the flavor out and removes the starches that make acorns good to bake with, so it's more appropriate for uses that keep the nuts more-or-less whole, like making these delicious-looking pickled acorns. To do the hot-leach method, place your acorns into a pot and cover with a few inches of fresh water. Bring to a boil and boil for 5-10 minutes, then strain the water out. Repeat the process until the acorns are no longer bitter. It took me about 30 changes of water to leach the tannins out of this batch (I saved the water from the first few strains to use as a fabric mordant, see below.) *Note: I have read on other instructions that the acorns should not be temperature-shocked because it makes the tannins permanently bind with the proteins. They say you should have two pots of water going at once and switch the acorns back and forth between them. While they are boiling in one pot, bring another pot up to a boil and then transfer them. Then dump the water out of the first pot and add new water and bring to a boil and transfer them into it. And so on... I tried both the "hot to hot" method and the first one mentioned above and couldn't tell much of a difference, but it is worth mentioning.
So what did I do with my acorn bounty? Well I tried that recipe for spiced pickled acorns above, and they tasted amazing! I was really happy with the flavors- you could still taste the flavor of the acorns through the tasty spices.
Then I did a quick test-run of the flour by making myself some pancakes. I didn't have super high hopes because the flour no longer smelled warm and maple-ey, but oh my goodness those pancakes were good! I just substituted half of the flour in my normal recipe for acorn flour. They were nutty and rich and a lovely brown color. They tasted amazing with some maple syrup.
I have some more recipes I want to try with this interesting ingredient. I wanted to make acorn flour profiteroles with maple cream filling (flavored with pine-nut infused whiskey) but alas, I had a terrible recipe for the cream puffs and they kept failing. I have since found a good recipe and plan to complete my testing as soon as I can. I was inspired by this recipe for boozy acorn macarons. Something about acorns, cream, and booze sounded so comforting that I had to try it out! Even though my cream puffs didn't turn out, I still made the whipped cream and the minions informed me that it was divine. I can't wait to put the pieces together finally. ;)
I also intend to make some adorable little acorn meringue cookies. I saw this adorable post from Sprinklebakes for acorn-shaped meringue treats and I thought "how cool would that be made with real acorns?" Her recipe is here, and I'm definitely going to return to it.
Want more? Here's a delicious-looking recipe for acorn gnocchi from one of my favorite bloggers. And here is a round-up of many acorn recipes, from sweet to savory and everything in-between. If you make something with acorns, I'd love to hear about it. Feel free to share in the comments below!
Other uses: Acorns make a fabulous fabric mordant to prepare fabric for dyeing, because they contain both tannins and proteins. I won't go into the nitty-gritty of this too much right now, but if you like dyeing fabrics then by all means save the water your acorns were leached in! You can also make a mordant by boiling the leftover shells and then letting them sit in the water overnight before straining and using as a mordant. When combined with iron, tannin mordants can produce very dark colors.
I'm going to be honest with you guys, processing acorns is A LOT OF WORK. Especially if you stubbornly choose acorns that are very high in tannins, which I did. I suppose if you found a nice white oak with low tannin acorns it would be totally worth it. But I had a hard time with this experiment because processing the acorns used a lot of my time and a lot of resources. So many pots of water to boil! So much good stuff down the sink! The acorns are delicious and I love using the flour, but honestly I don't think I will do this again unless I find acorns that are much lower in tannins naturally. If you still want to try some of the recipes, you can often find acorn flour at Asian markets.