Acorn Processing
Acorn processing — the collection, drying, shelling, grinding, and leaching of acorns to remove bitter tannins, producing a flour or paste used for porridge, bread, and soup — was the foundational food technology of the Indigenous peoples of California, the Eastern Woodlands, and anywhere oak trees grew in abundance. Acorns were the most important plant food for California's Indigenous nations (*Miwok*, *Pomo*, *Ohlone*, *Yokuts*, and many others) — the oak forests were managed through controlled burning to maximise acorn production, and the processing of acorns into food was a multi-day, multi-step technique that represents one of the most sophisticated food-processing traditions in pre-contact North America. The technique has been largely lost but is being revived through Indigenous food sovereignty efforts.
The complete acorn processing chain: 1) **Harvest** — collect mature acorns that have fallen naturally (late September-November). Select heavy, un-wormed nuts. 2) **Dry** — spread in a single layer and air-dry for 1-4 weeks until the shells become brittle. 3) **Shell** — crack shells with a stone or nutcracker and remove the nut meats. 4) **Grind** — pound the dried nut meats to a fine flour using a stone mortar and pestle (*bedrock mortar* — the grinding depressions visible in granite outcrops across California are the physical evidence of millennia of acorn processing). 5) **Leach** — the critical step. Acorn flour contains bitter tannins (tannic acid) that must be removed by running water through the flour repeatedly. Traditional method: the flour is placed in a sandy basin by a stream and water is poured through it for hours until the bitterness is gone. Modern method: place flour in a mesh bag and soak in multiple changes of water (6-12 hours, changing water every 2 hours) until a taste test reveals no bitterness. 6) **Use** — the leached flour is used wet (as a porridge or added to soups) or dried and stored as flour for bread and cakes.