Acorns are mentioned as an ingredient added along with herbs in 16th century Germany. “Ginger, anise, and cumin were used in beer in Germany and various other things including laurel, marjoram, mint, sage, and acorns were used at one time or another in addition to gruit.”
The Discovery Channel did a documentary entitled “How Beer Saved the World.” A snippet of transcript describes what is the first use of acorns to make beer in the new world, giving us a gray-area reference circa 1622:
“Beer was an absolute essential item for their survival.” [Dr. Greg Smith, Historian]
Narrator: When the beer supply ran out, the colony hung in the balance. The settlers had to find a way of making beer. But they had no barley or hops until squirrels came to the rescue. Sounds nuts, but they gave settlers the idea of using acorns, and it worked. Acorn beer kept Plymouth alive.
As stated earlier, acorns can be mashed. However, there are some pre-brewing actions that must occur in order to prepare acorns for brewing. First of all, acorns are very high in tannin. The choice of which species of oak to harvest can assist with the reduction in tannins. In general, acorns from the red and black oak families have more tannins, while those from the white oak family have less. If you are unsure of whether the acorns you are harvesting are from the white, red, or black oak families, a simple way to judge is by the size of the acorn cap. The larger the cap, the more tannins contained in the acorn. If one is concerned about the authenticity of the specific species of oak, a good choice is the cork oak – a low tannin option that was cultivated throughout southern Europe in the middle ages, and which has migrated to North America. The cork oak produces acorns that are long and slender, shaped similar to a football when the cap is removed.
To harvest the acorns, pick them directly from the tree or soon enough after they fall that they have not yet fallen prey to rodents or insects. They should still be greenish in color, as that ensures they are fresh. In order to ensure that the acorns are suitable for consumption, remove the caps and drop the nut into a bowl of water. If it floats, this is evidence that the core has been hollowed out – generally by a type of larva called an acorn grub or oak weevil. You can also do a visual check for small holes, caused by the grub gnawing its way out of the husk.
Once the acorns are harvested, decide whether you want to convert them directly into an adjunct or if you want to mash them as a principle fermentable. If you decide you want to mash them, treat them the same way as raw barley. Allow them to sprout – a sprout of less than an inch is sufficient to indicate that the acorn has begun transforming its starches into convertible sugars. “What I do to prep acorns for consumption is let them germinate, so the starches turn into malt sugar.” Once they have sprouted, you can continue on with the next steps. If you are planning to use them only as an adjunct, you can proceed directly from harvesting to the next step.
Shell them. Once the cap is removed, set the acorn in a hard surface and crack it with a hammer. Once the shell is cracked, it should peel away fairly easily. It will be even easier if the acorn is soaked through. If the acorns were harvested green, they can be shelled with a paring knife. Once you have collected the nut meats, choose the leeching method best suited for your final purposes. For making bread or mashing, use the cold water method. For use as an adjunct, you can use the faster boiling method.
To use the boiling method, use two pots of water. Boil the acorn meats in one pot while the second pot heats to boil. The water in the first pot will darken. When it turns brown, pour off the water and immediately place the acorn meats in the second pot. Do not allow them to cool in between, or you risk binding the tannins to the starches. Once the meats are in the second pot, fill the first pot with fresh water and begin heating it back to a boil. Repeat this process until the water no longer changes color. It should take between 2 and 4 hours, depending on the tannin content of the acorns.
To use the cold water method, crush the shelled acorns, place the ground pieces in cool water and leave sit until the water turns brown. Pour off the water and replace it with clear water. Repeat this process until the water no longer changes color. This could take anywhere from 3 or 4 days to more than a week depending on the level of tannin in the acorns. Bear in mind that Shaw is discussing cold leeching from the perspective of making flour for bread… not adjuncts for beer. You do not want to use cheesecloth to strain the water (since you do not want to preserve the oils or proteins), and you do not want to grind your acorns to flour (as the glutens remaining from cold leeching will cause your mash to gum up and you will be unable to properly sparge.)
Once the leeching produces no change in water color, dry out the nut meat by placing it in the sun, or by placing it in the oven with a heat setting of 200 degrees Fahrenheit for two hours. You don’t want to roast the acorns… you just want to dry them out so they do not mold. At this point, you should have some rather bland-tasting acorn bits. From this point on, if you allowed your acorns to sprout, you can treat the acorn meal just as you would treat malted barley. You can also change out barley pound-for-pound in your beer recipes, although you may find that leaving some barley in the mix will improve the overall flavor. If you used the boiling method of leeching, or you did not allow your acorns to sprout, you can still use the acorns in your brew; but they will not significantly contribute to fermentation. Treat them as you would rice syrup solids or unmalted barley when formulating your recipe. In this case, if you want a nuttier flavor from the acorns, it is okay to roast them at 350 degrees Fahrenheit for enough time to achieve a desired color.
 Unger, pg. 32; referencing A. Hallema and J.A. Emems, Het bier en zijn brouwers. Die geschiendenis van onze oudste volksdrank (Amsterdam, J.H. deBussy, 1968), 29; Moulin, “Biere houblonet cervoise” 117; Schulte, “Vom Grutbiere, 130; Nordlund, Brewing and Beer Tradtions in Norway, 126, 132-34, 144, 158-59, 173-93, 217-19, 225-26.
 Discovery Communications, Inc.
 Shaw, 2013.
 Ocean, pg. 2
 Deane, a quote from biologist and nutritionist Peter Becker regarding acorns.
 Shaw, 2013
Alden, Lori (2005). “Nuts”. The Cook’s Thesaurus. Retrieved 25 June 2016, from http://www.foodsubs.com/Nuts.html.
Deane, Green (2014). “Acorns: The Inside Story”. Eat the Weeds and Other Things Too. Retrieved 23 June 2016, from http://www.eattheweeds.com/acorns-the-inside-story.
Discovery Communications, Inc. (2011). How Beer Saved the World. Produced for the Discovery Channel by Beyond Productions, PTY LTD. Narrated by Henry Strozier. Transcript by Daniel J. Leonard. Retrieved 23 June 2016, from http://www.beersyndicate.com/blog/how-beer-saved-the-world-transcript.
Ocean, Suellen (1993). Acorns and Eat ‘Em: A How-To Vegetarian Cookbook, Complete Directions for Harvesting, Preparing, Cooking Acorns. Grass Valley: Ocean-Hose Publishing.
Shaw, Hank (26 September 2013). “The Best Way to Make Acorn Flour”. Hunter, Angler, Gardener, Cook. Retrieved 24 June 2016, from http://honest-food.net/2013/09/26/acorn-flour-recipe-cold-process.
Unger, Richard W. (2004). Beer in the Middle Ages and Renaissance. Philadelphia: University of Pennsylvania Press.
Whistler, Randy (November 1997). “The Adjuncts: Malt Madness”. Brew Your Own. Retrieved 23 June 2016, from https://byo.com/hops/item/1463-the-adjuncts-malt-madness.