Collecting acorns to eat - how/when? Acorns of many oak species are edible.
They've been used as food in many traditions, but almost all need boiling and/or soaking to leach out the tannins.   I'm curious to try them, as nuts, a hot drink, or ground into flour for baking. I'm particularly interested in the European Oak (a.k.a Quercus robur, English or Common Oak) as I have several growing over my garden.
I've found plenty of sources on how to prepare them, but little on how to select them.  I assume they should be brown to be ripe, but do I need to get up and pick them as soon as they turn brown, or are fallen ones good?  Apart from obvious signs that something has started eating them, is there anything I should beware of?
Update:
Even after discarding the floaters I had to throw away quite a few.  they were quickest to shell by quartering them lengthways with a sharp knife.
Unroasted ground acorns worked well in place of ground almonds in a biscuit (cookie) recipe, but the coffee substitute has a flavour closer to malty than nutty and isn't great.  I may not have roasted the acorns enough, because despite leaching until they weren't bitter, they turned dark brown on drying so I couldn't see how roasted they were.
While I have never collected acorns to eat, only to feed to animals, I have foraged and served beechnuts and chestnuts, and the same principles apply.
Ripe acorns will fall - so picking them up from under the tree is perfectly fine, no need to climb and risk anything.
As for most nuts, fallen acorns are protected by the outer shell and can withstand being on the ground for a bit. As they need a cold phase to germinate, they will remain mostly unchanged during the autumn, giving you a generous window to go out and forage.
You want to pick large and plump acorns, leave small, cracked, soft or otherwise damaged ones to the wild animals. You should wash them when you bring them home1 or before processing them. This is also a good occasion to sort out the random hollow acorn, because they will float.
Then proceed as per your chosen recipe.
1 If you don’t process them immediately after foraging, make sure they are dry on the surface to prevent mold.