Decoction is a method of extraction by boiling of dissolved chemicals, or herbal or plant material, which may include stems, roots, bark and rhizomes. Decoction involves first mashing, and then boiling in water to extract oils, volatile organic compounds, and other chemical substances. The process can also be applied to meats and vegetables to prepare bouillon or stock.
A decoction is also the name for the resulting fluid. Decoctions differ from most teas, infusions, or tisanes, in that they are usually boiled. The term is used colloquially in South India to refer to black coffee prepared by the traditional method.
[from wikipedia] Use
In brewing decoction mashing is the traditional method where a portion of the mash is removed to a separate vessel, boiled for a time and then returned to the main mash, raising the mash to the next temperature step.
In herbalism, decoctions are usually made to extract fluids from hard plant materials such as roots and bark. To achieve this, the plant material is usually boiled for 8–10 minutes in water. It is then strained.