Few people today know the delight of gathering wild mushrooms, greens, tubers, rhizomes, flowers, stems, buds, seeds, and acorns or other nuts for their own sustenance.
One example I collected this year is the acorn of the Burr Oak, a variety of White Oak common to Missouri and many other states. This year I gathered more than 60 pounds of these acorns for processing into something edible, as well as 15 pounds of the "common" White Oak acorns. While most of the latter were gathered a bit too late due to worm holes in about 50% of them, the Burr Oak acorns were a bumper crop I gathered first thing every morning.
The secret to finding intact acorns seems to relate to the time before they fall. Begin observing your favorite trees some weeks before acorns begin to drop. I did this and noticed fat, green acorns up among the leaves and grossly underestimated the number present. Then I started harvesting when they began falling, but eventually stopped collecting before they stopped falling. Waiting till they are all over the ground is a sure way to gather many which have been there for days or even weeks and are riddled with worm holes.
There are five main activities in processing acorns: gathering; removing outer coverings; grinding; removing tannins by repeated waterbath leachings until water clears; and drying. The internet, as well as books, are good resources for learning the details and it is best to read a number of different sources, as they usually differ, and as you try methods you will discover what works best for you. Some suggest leaching the acorns before grinding; others grind first, then leach. Your own time, physical ability, household infrastructure, and other factors will help determine which methods you prefer.
These Burr Oak acorns seem to have more tannin than I recall from several years ago. Or, there is the possibility that I did not spend enough time leaching previous batches, leaving more residual tannins. Two main reasons to my knowledge for removing tannins is that 1) the human kidney cannot handle tannins in the amount they are found in acorns, even from the white oaks which are known to produce a lower amount of tannin than do red oak acorns; and 2) the presence of tannins in food leads to insomnia in some.
I have attached a photo showing four sample Burr Oak acorns from this year, each in a different stage of processing. There are actually four layers that must be removed before reaching that beautiful, off-white nut inside, which resembles a chestnut in color and size (after it has also been dehulled). The most prominent layer is the characteristic outer "burr" after which the tree is named. The next three layers can sometimes be removed as two layers, depending on how much drying the nuts do after the burrs have been removed. After removing the burr, and then the next, semi-rigid layer, one can remove the next two layers together if the nut has dried a day or so first. If the nut is totally fresh, removing the final layer involves much fingernail scraping.
After all leaching and grinding is done, then the pulp can be oven-dried (not too hot), or dehydrated slightly slower on top of a carefully watched wood stove. If the pulp is not dried, but is immediately frozen, the entire mass must be thawed as a unit unless you plan on using some heavy duty tools (? small mattock?) to break it into parts.
The dried, ground pulp or meal is your acorn flour and can be mixed with other flours for a variety of products including crackers, flatbreads, cookies, cakes, and breads. Experiment and remember that when you ingest tree nuts of any kind, you are ingesting a mix of minerals you will not find in shallow rooted garden plants. And also ponder that Native Americans were first, and best, at this practice and we still have much to learn from them.
Experiment and enjoy!