It's that time of year! We've collected a lot of acorns, mostly from the Tanbark Oak (Lithocarpus densiflorus), time to make flour!
If these were their close relatives, chestnuts, the process would be simple: shell, dry, grind. These acorns are full of tannins (the stuff that makes tea brown usually), so a few additional steps are involved.
Key things to keep in mind:
1. Dry the acorns as quickly as easily possible without heating them - we spread them in layers an inch or two deep on screens where there is good dry air circulation for a month or two. Acorns are susceptible to mold if stored moist for very long.
2. Do not heat acorns until you are completely finished with preparation of the edible flour and are preparing the final food item - heating these nuts or their flour early ruins the texture and prevents their "gluten-like" materials from showing their amazing properties.
Here are the steps we follow, in order:
Step 1 - Start with shelling the acorns. I have built power machines for doing this, which are messy and I am still unconvinced they saved any time, net. What I do these days for small batches is simply sit at the table while chatting, watching programs, or sitting by the fireplace, and simply shell them by hand using a basic nut cracker. There are several approaches, cracking at the cap end (the white oval is at this end) seems to work best for me, though others have good success putting the nut longwise into the nut cracker. Experiment and find what works for you. Discard any nuts that are moldy, darkened, contain bugs, or otherwise look "off". The shells and discarded nuts we use as mulch in the garden, they do compost given a bit of time.
Shelled acorns for Tanoak acorns look like this, note that not all acorns will have the papery husks.
Step 2 - Remove the husks. Not all acorns have these, so if you have exposed nut meats right after shelling, skip this part. This step is optional - it doesn't seem to be too much of a problem (or even frankly detectable) if the husks are ground with the nuts, I just do this because if the nuts are dry the husks generally fall off easily and it makes examination of the nuts to see if there are hidden bad spots much easier. If the nuts are dry, the husks are just going to fall off by rubbing handfulls of acorns between your hands. The chaff can then be blown off gently or the nuts picked out of the chaff. Discard any acorns with unusual coloration.
Step 3 - Grind the acorns. We put them in a kitchen blender and cover them with tap water until they are covered. Using a medium speed at first, and a high speed later, we grind the acorns into something with the consistency of a "smoothie".
Step 4 - Leach the acorns. We lay out a set of old towels on a screen (lots of ways to do this), with a relatively smooth and fine weave kitchen towel as the top layer. By using some rolling of the edges of the towels a raised rim can be made that helps keep the acorn paste in the center of the towel. Use a spatula to spread the paste out so it is fairly uniformly thick. This is the acorn cake you will leach. Acorn meal exposed to air will darken slightly, which is not a problem. Shown below is an improvised leaching stack on a plastic garden chair. Note - the towels will be permanently stained by this process.
Step 5 - Dry the acorn cake. We allow the wet cake to drip for half an hour, then carefully fold the towel corners over the cake. We take this and compress it between layers of dry, clean, rag towels. You can put a cinder block atop the stack or other weight that doesn't care about getting moist. Let it dewater for an hour or so. If you can still squeeze water out by pinching some between your fingers, it needs another pressing with dry rag towels.
Once this initial dewatering is done, we place it on a warm, dry (not hot!) place and set up a slow fan near it. Leave it on the towel - it will continue to wick water out of the cake and help the drying. When the surface of the cake is dry, fold the towel ontop of it and crush the cake into lumps. The middle should be moist still. Allow the lumps (break into half inch or smaller clumps) to dry to the touch, then crumble them up and repeat until the crumbles are dry. Continue the drying for another few hours just to be certain.
Step 6 - Make "flour". In our case, we just put the dry acorn meal back into the blender and pulse it a few times to make a flour-like powder. This is now ready for use. Store in an airtight container in the freezer until ready to use.
Asking my son what he would like people to know about the process, he replied "when do we get to make acorn chocolate chip cookies?".
Up soon, Acorn Chocolate Chip Cookies!