炮制

Pao zhi is a discipline distinctive to Chinese materia medica: the systematic preparation of raw plant, mineral, and animal materials before they enter a prescription. Through cleaning, cutting, and various forms of processing — frying, steaming, calcining, soaking — the practitioner can alter an herb's properties, amplify or restrain its effects, reduce or eliminate its toxicity, and make it easier to store and to take. A single plant in raw, honey-fried, wine-fried, and charred forms is in clinical practice four different medicines, each with its own indications. This is one of the most distinctive techniques of the Chinese pharmacy.

The methods of pao zhi were refined across many centuries and reached classical maturity in the Ming and Qing dynasties. The earliest dedicated treatise — the Master Lei's Treatise on Processing (《雷公炮炙論》) — dates to the early medieval period, and many later monographs followed. The modern Chinese Pharmacopoeia codifies processing standards for common decoction pieces.

Dry-frying (炒, chǎo) — frying without liquid additives, sometimes with bran or earth as a heat buffer. Used to moderate harsh natures, strengthen Spleen-tonifying functions, or enhance the ability to stop bleeding.

Liquid-frying (炙, zhì) — frying with a liquid additive that imparts its own properties. Honey-frying (蜜炙) moistens the Lung, soothes cough, and strengthens supplementing actions (honey-fried astragalus, honey-fried licorice are the most common examples). Wine-frying (酒炙) invigorates blood, frees the channels, and lifts the action of the herb upward (wine-fried rhubarb is much milder and more upward-directed than the raw form). Vinegar-frying (醋炙) directs the herb into the Liver and astringes for pain relief (vinegar-fried bupleurum, vinegar-fried cyperus). Salt-frying (盐炙) directs the herb downward and into the Kidney (salt-fried eucommia, salt-fried morinda). Ginger-juice-frying (姜汁炙) warms the middle, restrains nausea, and reduces toxicity (ginger-prepared pinellia is the standard form because raw pinellia is too harsh and toxic to use directly).

Calcination (煅, duàn) — heating to high temperature so that the herb becomes brittle and easy to powder, and so that its properties are altered. Used chiefly for minerals and shells.

Steaming (蒸, zhēng) — steaming with water or with wine. Most famously used for prepared rehmannia (熟地黄, Shú Dì Huáng), which is steamed and sun-dried in repeated cycles (classically nine times each). The repeated processing transforms it from raw rehmannia, which cools the blood and generates fluids, into prepared rehmannia, which tonifies blood and nourishes yin — a different medicine for different purposes.

Charring (炒炭, chǎo tàn) — frying until the outside is black and the inside scorched brown, while the herb's essential nature is preserved ("retaining the nature" — 存性). Charred herbs gain the ability to stop bleeding. Charred rhubarb, for example, no longer purges aggressively but instead stops bleeding from heat.

These examples cover only the broad categories. The specific method appropriate to each herb, and the clinical purpose served by each version of it, represents centuries of accumulated experience.