All acorns are edible, but high levels of tannin make them taste bitter. Of the two major groups of oak trees, acorns from the white oak group are less bitter than those from the red oaks.
Sweeter acorns may be eaten raw or roasted, but they still may be too bitter for some palates. Since tannin is water soluble, boiling acorns in water leaches out the bitterness. Replace the water when it turns yellow, and repeat the boiling process, using fresh water as needed, until the water remains clear. Once the acorns are tannin-free, dry them on a baking sheet in the oven before cracking the shells and picking out the nut meat or grinding the acorns into a meal and using it like flour.