To Process Acorns:
Pick acorns. Just ripened is ideal, but in New Mexico I have often picked them while still a bit green. Be sure there are no holes on the surface of the acorn shell, which indicates worms. Once you get them home, the sooner you can roast them in the oven the better. If you can’t do this right away, stick them in containers in the freezer, and roast them as soon as you get time. Roast them (with the shells on) at 300 degrees until the nuts inside the shells darken and become fairly hard, if you’re using them for cooking after roasting. The length of roasting time will differ according to the size of the acorns. If roasting for storage not in a freezer, cook them until the nuts inside the shells are very dark brown and your fingernail will not make even a tiny dent in a nut, but take them out before they blacken. Then you can store them in glass jars or, preferably, food grade plastic containers with some holes punched into the tops of the containers, for some air ventilation to prevent mold. After shelling, in my experience, the hard nuts can be kept in glass jars for at least a year, although this may be different in damper climates, I’m not sure.
To make Acorn Meal for baking and cooking, cover the roasted acorns with water and cook for 30 minutes at a time. After 30 minutes, taste the acorns and change the water if they seem too astringent. Cook for another 30 minutes, then check them again. Change the water and repeat as long as needed. Keep in mind that some of the acorn flavor is also lost with each leaching round, so a little bit of astringency might be preferable to none at all. go by your own taste. Keep the water from the last leaching round to use for flavoring soups, baked goods, and more.
After the acorns are leached, drain them, and then grind them up with a mortar and pestle or in a food processor, scraping down the sides of the work bowl a few times as you grind them up, if using the machine.