Acorns (Quercus spp.) have long been thought of as a last resort food, but these small parcels of goodness pack quite a nutritional punch when processed the right way. Processing them is important, as acorns (like tea, chocolate and red wine) are jam-packed full of tannins. So much tannic acid in fact that they’re toxic to many livestock and even humans in their natural form. Leaching them of their tannins takes a little time and dedication. You also have to wait for trees to produce a mast crop every four or so years, though for the enthusiastic forager this can involve many enjoyable months of scouting these beautiful trees in the lead up to autumn. Patience certainly is a virtue where acorns are concerned, as they can reward you with easy to store sweet and nutty flour, and a cheap, cheerful and fattening winter feed for chooks and pigs.
Oaks are a majestic long-lived tree, native to the Northern Hemisphere. There are incredibly beautiful and productive specimens in early European settlement areas, where colonists were keen to replicate scenes from home. Oaks grow well across south-eastern Australia—so well that they have naturalised in many areas. In their native habitat, oaks are found across the Northern Hemisphere from England to the Americas, and the story of their incredible migration across this hemisphere (via squirrel) is a fascinating botanical study.
The best eating acorns (which contain the least tannic acid) are those of the North American white oak section (e.g. Q. alba, Q. bicolor). They aren’t overly common in Australia, but certainly can be found, especially in older parks and botanical gardens. English Oaks (Q. robur) are generally lower in tannins and are far more ubiquitous in parks, streets, railway sidings and paddocks across South Eastern Australia. Holm Oaks (Q. ilex) are an evergreen species also known for having particularly good eating acorns. Oaks that may be found in Australia but are best avoided due to the bitterness of their acorns include Cork Oak (Q. suber), Turkey Oak (Q. cerris), Pin Oak (Q. palustris) and the Northern Red Oak (Q. rubra).
There are hundreds of other species of oak, which can make identifying the exact species of a wild specimen difficult, but sampling acorns from different wild stands will help you to work out which ones you prefer. In general when looking for eating acorns, look for lobe-edged leaves and large, robust acorns in tough shells under cup-shaped cupules.
Acorns may be hot or cold leached of their tannins with water through various methods. Hot leaching is done by boiling and draining the acorns repeatedly until your water runs clear. This can be done in an afternoon. Cold leaching is done with cold water and ground acorns over the course of several weeks.
The waste water from this process may be used in natural dyeing, as tannic acid is a common mordant, throwing variations of fawn. The processed nuts can be fed fresh to animals (chooks and pigs will tolerate far more bitterness than humans will) or dried, either for storing whole or grinding into acorn flour. You can make acorn flour by grinding it in a flour mill. Acorn flour is gluten-free and has a similar texture to almond meal. It has a naturally sweet, nutty flavor so it is well-suited for use in biscuits, cakes and other treats. Acorn coffee can also be made by roasting processed nuts, grinding and then roasting again.