Roots, barks and fruits being thicker and less permeable than the aerial parts of medicinal plants, do not liberate their active principles by simple infusion. It is necessary to simmer these parts in boiling water in order to extract their medicinal constituents. The material should be cut or broken into small pieces. In order to avoid loosing volatile constituents, use a lid over the simmering pan. After cooling down and separating the solid from the liquid, decoctions can be taken hot or cold.