Mix with boiling water and press out liquid through a cheesecloth. With very bitter acorns, repeat this process several times. This meal will cake during the drying process. Regrind using a food chopper. Then, seal in containers, preferably glass jars.
All acorns contain tannic acid or tannin.
This is what causes the bitter taste, the same as the soft brown lining in pecans that we have all tasted if we have cracked open pecans and eaten them raw. The white oak family has less tannin than the black oak family. THe white oak family acorns I have tried are White Oak, Burr Oak, and Club Oak. There are many varieties. White oaks have rounded leaves.