I didn't know you could eat acorns until I read it in The Urban Homestead. They are edible but they need to be processed because they contain too much tannin to be eaten otherwise. They can make you quite sick in their unprocessed state, but they are so bitter from the tannins that you aren't likely to eat enough to be a problem.
Once I knew they were food, I was sort of floored looking around at all the acorns sitting around, crunching underfoot, going to waste. My environment seemed more productive, more fertile, more useful. I started to forage through the city for acorns when I was looking for apples and blackberries. I thought I would share the preparation method with you; I will post some recipes using the acorns in the next couple weeks. This a nice fall activity especially if you can rope in a few friends to help you work; have an acorn shucking bee.
Forage: locate and obtain a large quantity of acorns. Using acorns off the ground is fine, just make sure to take only perfect, intact acorns. No cracks or holes or soft acorns. Acorns with holes in them generally contain rather unpleasant little maggots that I prefer to avoid. Acorns with green shells are fine as long as their meat is not green.
Prep: put acorns in a sink or bucket full of water. Discard acorns that float.
Peel/smash/crack open the shells and remove the white meat. Discard acorn flesh that is discoloured or mealy, it may be spoiled.
Smash up the flesh with some water in a blender. Take resulting mush and drain it over a colander lined with cheesecloth or a tea towel.
Gather up the cloth around the mash and dip it into water until the water is cloudy. Discard water, repeat until water is clear. Your mash is now free from bitter tannins.
Eat locally, eat for free, eat like a squirrel.