In the Old World, acorns have been eaten by humans since Paleolithic times. They must have been an important food in pre-agricultural times, for as agriculture became more and more important in the Middle East and Europe, the practice of eating acorns declined and was even looked down upon by some cultures. The Arcadians of ancient Greece ate acorns, but the civilized Greeks considered the Arcadians to be rustic and primitive. In the Persian Empire, acorns might be eaten by mountain tribes or poor peasants, but they were not suitable for sophisticated city dwellers. The Romans knew that the Spanish ate acorns and this was proof to the Romans that the Spanish were barbarians, though some Italians had to resort to eating acorns during food shortages after the fall of the empire. In the American South, during the Civil War, acorns were used as a coffee substitute. They were also used this way in Germany during times of shortage. The report is that acorn "coffee" is nasty stuff.
Not all agricultural people forsook acorn. The Native Americans of what is now the eastern United States ate acorns to a limited degree. The Arizona Indians would eat naturally sweet acorns but did not bother with bitter acorns that needed to be leached to be made edible. In modern Korea, acorn starch is used to make a gelatin called dotori muk. This is used in salads. Acorn flour is used to make noodles called dotori gooksoo. Both acorn products can be purchased in Korean grocery stores in the United States.
Possibly the people to whom acorns were of most importance were the California Indians . The California Indians did not practice agriculture, but at least nineteen different species of oaks are found in California. Depending on the tribe and the acorn production of any given year, acorns could make up 60% of the diet. In many areas, more than one species of oak was present, and this lead to the development of favorite species for food. A species might be favored because of the taste or because it was easier to process. Some of the very favorites were California black oak (Quercus kelloggii), coast live oak (Quercus agrifolia), canyon live oak (Quercus chrysolepis), and valley oak (Quercus lobata). Scrub oak (Quercus berberidifolia) was a last resort.
Gathering acorns was not totally without risk. Grizzly bears once roamed over most of non-desert California and they were fond of acorns. However, acorn gathering by humans was a group activity and there would be many pairs of eyes to watch for danger. Also, bears would likely avoid a noisy group of humans. There also was some acorn gathering etiquette. Certain trees might be owned by certain families or certain groves might be owned by certain villages. Gathering from another village's grove could be grounds for war. These unwritten property laws were as binding as any modern deed in the county courthouse. If you wanted acorns, you traded for them. Thus, in times of surplus, the people who had acorns would trade them for things like pine nuts, obsidian, soapstone, and pigment minerals.
Obtaining the acorns was the easy part. The hard part was processing them. Women did the processing. It was so much work that the Cahuilla believed that bitter acorns were a curse from the Creator. Some acorns, including those of Californian species, contain tannin. Tannin serves the oak as a fire retardant, but it also makes the acorns bitter. Tannin is also poisonous to humans and too much of it causes kidney failure. However, ways were developed for removing the tannin. Imagine what great discoveries these were. An abundant but poisonous item could now become the basis of the entire diet. One method of removing the tannin would be to bury the shelled acorns in mud for several weeks. This was not terribly labor intensive, but it did mean that there was a waiting period before they acorns would be edible. The more common method for removing the tannin was to grind the acorns into flour and pour water over the flour until the tannin was gone.
Grinding was done using various mortar and pestle type devices. One was the bedrock mortar. Dried and shelled acorns were simply pounded into meal on a large, flat rock using a smaller rock. With time, the depressions created by this process could get several inches deep. This was good because then the meal wouldn't scatter as it was pounded. In shallower depression, the grinding may have been done with a smooth, palm-sized river rock, but with deeper depressions, a rock that had been deliberately shaped like a pestle would have to be used. If the mortar rock was large enough, there would often be multiple depressions. Making grinding a group activity probably made the work a little less tedious. Since bedrock mortars are impossibly heavy and very fire-resistant, they are one of the few tangible pieces of California Indian life that can still be seen in their original locations. Slightly more portable mortars were also made from rocks that could be carried. These rocks would be about the size of a bathroom sink and still would be quite heavy, so they probably were rarely moved. Some peoples would glue a bottomless basket around the depression to keep the meal from scattering. The third type of mortar was the most sophisticated. This would be a stone bowl, taller than it was wide, with walls an inch or so thick and holding approximately a gallon. These were made by hand, of course, but were as round and smooth as if they had been turned on a lathe.
Next came leaching out the tannin. Meal might be placed in a basket and water poured through until it was no longer brown. Another method was to leach the meal on the ground. A shallow pit was made and lined with sand. On top of the sand was placed leaves or pine needles and the meal was placed on top of that. Water was poured onto the meal until it was felt that it was sufficiently leached.
Grinding and leaching would have to have been done daily or nearly every day. Whole acorns could be stored for a year or more, but once the meal was wet from leaching, it would have to be used fairly soon before it could spoil. The mush might be baked or steamed in an oven or pit to make bread. It might be cooked on stone griddles to make a something like tortillas or pitas. It also might be made into a porridge or soup. This could be heated up in a stone bowl, but the most common method was to heat it up in a basket - yes, a basket. The vast majority of the California Indians did not make pottery but where very skilled at making baskets. To heat food in a basket, hot stones were taken out of the fire, cleaned, and placed in the basket with the food. The stones were stirred quickly to keep from burning the basket.
When the Spanish conquered coastal California, they wanted to turn the Natives into good Spanish citizens. That included teaching them "civilized" arts like agriculture and forcing them to abandon the hunter/gatherer lifestyle. Settlement and conflicting ways of land usage and ownership by "Anglos" and other non-Natives further disrupted the traditional practices. Modern California Indians live like most other Americans, but some like to connect with their history and heritage by harvesting, preparing, and eating acorn. They might gather the acorns in plastic bags, grind them in a food processor, leach the meal in a cloth-lined colander in the kitchen sink, store leached meal in the freezer, and cook it on an electric stove, but the spirit of the tradition lives on.
What does acorn taste like? I have tried valley oak. This is a species fairly low in tannin so I have tried a little bit raw and unleached. The texture is like a raw chestnut. (Oaks and chestnuts are related.) The taste is like a bland chestnut with no sweetness. I also made some meal by grinding acorns in the blender and leaching them in a cloth-lined colander. (The report is that acorns high in tannin will permanently stain the cloth, so if you are going to try this, don't use your best dish towels.) I ending up with about 3/4 cup of meal which a substituted for an equivalent amount of wheat flour and made vanilla chip cookies. It was a long time ago that I did this, but I don't recall the taste being any different from regular cookies. Acorn - or at least valley oak acorn - appears to be something that can be added to add substance to a food without changing the taste. I have not read any accounts of California Indians adding anything to their acorn foods, but I would imagine that at least some of the time they might add berries, aromatic leaves, meat, honey, or salt.
So, what are you going to do with all of those acorns that you have to pick up before you mow the lawn? How about some balanophagy? Take one of your favorite recipes that is heavy on starches like dried beans, wheat flour, or cornmeal, and substitute some of it with acorn meal. If you like the result, experiment with using all acorn meal. Invent your own recipes. There are recipes on the internet. Be adventurous. Have fun with it.
Photos property of Kelli Kallenborn. Photos from top to bottom:
Scrub jay with valley oak acorn;
Scrub oak acorns;
Valley oak acorns;
Chumash Indian bedrock mortar;
Coast live oak acorns;
Valley oak acorns from a well-watered tree.
 In this article, the term California Indians refers to the Natives of the California cultural province, which is the area of what is now California that is west of the deserts.