Well, I've heard about this for years and being into bushcrafting I've always fancied trying it out for myself.
Earlier this year when I noticed a good acorn crop from several mighty oaks, I thought I'd give it a go.
* Just a note though: Thanks to some great responses by my viewers I would like to add Acorns contain a lot of tannin and need to be prepared to remove the excess before using.
On the good side though tannin gives them a tea and coffee-like quality and they were much used to make drinks in the past. Traditionally the acorns would have been shelled and soaked in a river for several days to leach out the tannins before being roasted.
Here's a wiki link to tell you more about it "http://en.m.wikipedia.org/wiki/Acorn"
Now, this acorn coffee doesn't actually dissolve like normal instant coffee so it does need to either go through a cafetiere or a coffee machine. Or even put it in a cut off section of tights, wrap a string round the top and use that as an infuser.
Step 1: COLLECT THE ACORNS
It's best to wait for the acorns to drop from the tree when they're brown, but you have to be quick as the cheeky squirrels are ready to gobble them up. Also if they've been lying on the ground too long you get little holes and maggots in them.
Gather them up and pop them in a bowl when you get back home. Clear away any cups or leaves etc and just have a closer look to see if they're ok. Any split, soft damaged or holy ones just discard, we threw them back in the woods for the squirrels.
Put a large pan on the stove, put the acorns in and fill it with water so it covers them. * Bring to boil and boil for 15mins, topping up the water if you need to. This will kill any maggots in them that you've missed and also soften the shell for easier shelling. Also this will remove the tannin in the acorns making them good to go.