How were acorns prepared for food by Native Americans in North America?

Native American tribes, particularly in California, developed specific procedures to make acorns edible for human consumption.1

While acorns are a natural food source provided by the oak tree, they contain bitter tannic acid that must be removed before they can be safely eaten. To process them, these tribes developed techniques to leach out the toxins, rendering the nuts palatable. Once the bitterness was removed, the acorns could be used in various ways, including being ground into a flour.213