Habitat
Type: woods, hedges
Distribution: throughout northern hemisphere

General
Growth type: tree
Cycle: deciduous
Height: up to 35 meters
Other:

Leaf
Shape: oblong
Edge: rounded lobes
Other: base lobes overlap stalk

Trunk
Colour: grey-brown
Texture: rugged

Flower
Shape: catkin
When: April to May with leaves
Other:
Colour:

Seed
Shape: oval
Colour: mid brown when ripe
Size: 20mm
Casing: hard, smooth, with scaly cap

Contains tannin in high concentrations, especially in the acorns of Red Oak species. Tannin binds with protein, can interfere with iron absorption and can cause gastric pain, irritation to organs and liver damage. It is bitter and astringent and colours water dark. It may be reduced or removed by leaching in several changes of water, until it runs clear (not brown). Baking soda added to the water may speed up the process. Tannin breaks down with time.

May and June
all year
September to February

Parts with black and white icons are for non-culinary use

Flavour
Rating and Description:
bitter

How to Consume
fermented
cooked, roasted, flour

Special preparation
Grind for flour, or roast for coffee substitute. Grinding up the acorns will speed leaching.

To remove the bitter and toxic tannin pre-boil to soften shell, remove shell and boil in several changes of water. Alternatively, steep ground acorns in running water (like a stream) for 2-4 days, wrapped in cheesecloth or similar fabric.

Untested method with theoretical potential: Sprouting supposedly destroys some or all of the tannin, however, it also makes the acorn woody through lignin formation. A possible way to break down the tannin and lignin is to ferment the acorns with Lactobacillus plantarum using the same process as making sauerkraut. L. plantarum has the relatively unique ability to break down these substances. Fortunately, L. plantarum is ubiquitous and is likely to be one of the lactic bacteria to quickly colonise the brined acorns. It is also present in kefir culture (both milk and water kefir).

For more information on lactic fermentation see the Storage and Preparation page.

Nutrition
carbohydrates, fat, protein, ellagic acid

Used as ...
beverage
food, beverage (coffee substitute)

Action:
All used parts (including galls) anti-inflammatory, antiseptic, astringent, decongestant, haemostatic, tonic

May treat:
All used parts: chronic diarrhoea, dysentery, fevers, haemorrhages; external: wounds, skin eruptions, sweaty feet, piles, vaginal inflammation/discharge; mouth wash: mouth and throat infections

(bark): tannin
(galls): tannin, dye; ink: black (plus iron salt), brown (plus alum), yellow (plus tin salt)
(trunk): timber

Collection
(galls): after insects hatch
(bark): from 5-12 year old branches
collect brown acorns from ground; tree does not produce seed every year

Drying
(bark) dry to store

Note
A very valuable wildlife tree.

Plant parts:
leaf
stem or trunk
sap
root, bulb, tuber and other below ground parts
flower
fruit
seed

Parts with black and white icons in the availability section are for non-culinary use

Use:
culinary use
medicinal use
household use

Other:
caution

General Glossary

• lignin: substance forming woody cell walls

Glossary of Medicinal Terms and Nutritive Substances

• anti-inflammatory: reduces inflammation of joints, injuries etc. (see also demulcent, emollient)
• antiseptic: prevents putrefaction (applied to wounds)
• astringent: causes localised contraction of blood vessels and tissue, reducing the flow of blood, mucus, diarrhoea etc.
• decongestant: relieves congestion (see also expectorant and antitussive)
• ellagic acid: an antioxidant which may be beneficial against cancer, heart disease and other medical problems
• haemostatic: controls bleeding (see astringent)
• tonic: improves general health, bringing steady improvement