So, this thread is coming up to more than 3 years old. The acorns are starting to ripen on the Oaks, here in Hamburg, Germany and for the first time I thought to explore the idea of an Acorn Beer. Thanks for the thread, it's been good to read through others thoughts on the subject, unfortunate to find few that have given feedback based on real-world experience.
I know acorns from their use for making a coffee substitute. To process them, they need to be: peeled of the hard outer skin and the inner dark membrane leaving the creamish nut; leached in water (although some swear by milk, and from previous posts above, it is recommended to freeze them as well); roughly crushed; roasted - either lightly or dark depending on the strength of "coffeeness" desired; cooled; crushed; and, brewed.
So, this gives us several directions to explore: Obviously, a coffee stout using roasted acorns as the coffee substitute; another option is to lightly toast the acorns and then to cold press them to remove the oils, soak them in a food grade solvent to remove surface oil after pressing, wash the solvent away with hot water, ad then to dry the resultant meal which could then be used as part of a cereal mash. Again given that it might add murkiness, dark beers or ales may be preferable.
If the oil can be successfully removed and/or minimised, then it might be possible to mash (step mash) the resultant meal with some pale malt, or with the addition of amylase enzymes, sous vide, to convert the available starches, wash the meal and centrifuge/vacuum filter/filter under pressure through a membrane/crash chill and freeze filter, the liquid in order to clear it. This will definitely have an impact on the flavour profile of the final liquid, but then is should be easily addable to the end of the boil or post-boil directly into the fermenter.
Personally, I think a dark ale would be the best target style, combined with some filtration post-fermentation and judicious use of gelatine and carrageenan to help clear the resultant ale.
The acorns here are still some time away from being ripe and ready for use so, I still have time to research and think this through. If you have any input, thoughts or experience worth sharing, please do so.
Cheers.