A decoction is made by boiling water either fresh or dehydrated herbal substances with water or other fluids. A decoction is a chief method used to extract herbal constituents for use as fomentations, syrups, and enemas. We use the decoction for herbs that will not yield their active virtues at a lower temperature. Decoctions secure the soluble active principles of herbs that are hard or have a dense texture. This method is good for the roots, barks, and some seeds.
Some herbs should never be subjected to decoction. These herbs contain volatile principles (valerian root, peppermint), depends on resinous constituents (gumweed), or contain substances liable to be changed into insoluble and inert materials under boiling heat (marshmallow and slippery elm).
A decoction that includes aromatic herbs should be kept closely covered until it has cooled down. The herb to be decocted should be cut or ground. Some woody herbs could be reduced to a moderately fine powder, and soaked in cold water for 12 hours before bringing the water to boil. If fresh herbs are used in a decoction, the roots should be cut into very thin slices, leaves and whole herbs only moderately cut and woods should be cut in small pieces.
Glazed earthenwater, porcelain, or glass vessels should be used for preparing decoctions. The water used for the decoction should be clear water, rainwater, or distilled water.
Decoctions are intended for immediate use within 48 hours period. Preserving the decoction is difficult because of the decomposition of the starches and the mucilaginous principles. For these reasons, decoctions are made in small quantities.
The proper dosage of a decoction depends on the age, body, weight, and temperament f the individual. In general, give a cup of herbal tea three times a day.
Recipe : Place 1 ounce of the herb into a vessel with a cover. Pour upon it 500 ml of cold water. Cover the container and bring it slowly to a boil. Decrease the heat and simmer for 15 minutes. After decoction, press the herb hard to make sure all the solution is removed from the marc. Allow the decoction to cool and strain the liquid. Pour enough water through the marc to return the volume of water to 500 ml.
Herb that are well prepared by decoction: burdock seeds, dandelion root, echinacea root, ginger fresh, reishi, Chaga, willow, comfrey.
Reference: James Green, The herbal medicine–maker’s handbook: a home manual