Kashaya
The Ayurvedic decoction: herbs boiled down in water — the most direct extraction method in the traditional pharmacopoeia.
Kashaya (or kwatha) means decoction: herbs — most often hard parts such as roots, barks and seeds — boiled in water until the volume reduces, classically to a quarter or an eighth. The word also names the astringent taste when used as a rasa; the pharmaceutical sense is the more common one. It is the reference extraction method of the classical texts: simple, quick to prepare, immediately assimilable.
The traditional rule: one part of coarsely crushed herb to sixteen parts of water, simmered gently uncovered until reduced to a quarter, strained, and taken warm — often 30 to 60 ml before meals, as an indicative dose. A decoction is made fresh for the day and does not keep: it ferments quickly. Many other preparations derive from it: arishtas start from a kashaya, and medicated oils and ghees incorporate one during cooking.
Without knowing it, you may already practise kashaya: a cumin-coriander-fennel tea simmered for a few minutes, or a decoction of fresh ginger, are domestic versions of it. The principle is worth remembering: for the hard parts of a plant, a true decoction extracts far more than a simple infusion. To go further on what Ayurveda recommends drinking day to day, see our article on what to drink according to Ayurveda.