Processing of Chinese Herbs
Dr. Wu Boping
One of the unique characteristics of Traditional Chinese Medicine (TCM) is that the herbs must be processed before use. The processing of herbs is called "pao zhi" in Chinese. Since most Chinese herbs are from raw plant materials, processing is required to meet therapeutic requirements, ensure safety and produce satisfactory medicinal effect in clinical practice.
Purposes of Processing
Briefly, the purposes of pao zhi are as follows:
Removing or reducing the toxicity, and side effects of some raw herbs. For example, Chuan Wu (Radix Aconiti) and Cao Wu (Radix Aconiti Kusnezoffi) are good for relieving pain, but they must be processed to reduce their toxicity before they are used clinically.
Promoting therapeutic effects. For instance, the analgesic effect of Yan Hu Sou (Rhizoma Corydalis) is strengthened when it is processed with vinegar; and the effect of Kuan Dong Hua (Flos Farfarae) in ventilating the lung to stop cough is enhanced when this herb is stir-fried with honey.
Modifying its nature and action. Sheng Di, or raw Radix Rehmanniae, is cold in nature and has the effect of eliminating blood-heat, but, when this raw herb is processed, it becomes slightly warm in nature and is called Shu Di or steamed Radix Rehmanniae, and has the effect of nourishing blood and kidney's Yin. As another example, Da Huang (raw Radix et Rhizoma Rhei) often has the drastic effect of causing diarrhea, but the processed version of this herb which is steamed nine times, Shu Da Huang (also called steamed Rodix et Rhizoma Rhei), will only produce a mild relaxation of the bowels.
Facilitating the preparation and storage of herbs. Some processing is necessary to change the whole plant parts to a form that can be consumed and stored effectively. Most botanical herbs are immersed in water and softened, to make them easy to cut into segments or pieces. And most mineral and shell herbs, when heated to high temperatures and quenched, can then easily be ground to powder to be put into medicinal formulas.
Correcting the unpleasant flavor or tastes. As an example, rinsing with water eliminates the salty taste of Hai Zao (Sargassum) and Kun Bu (Thallus Laminariae).
Cleansing and purification. Some processing is needed to remove the non-pharmaceutical substances and other miscellaneous parts. Appropriate processing improves the herb's quality by making it clean, pure, and more convenient for patients to take. Examples of processing for cleansing and purification include: the brushing away of the hair of pi pa ye (Folium Eriobotryae) and the removal of the little thin green part at the center of the seed of Lian Zi (Lotus Seeds) before they can be used for medicinal purposes.
Methods of processing herbs
As you can see from the examples listed above there are a lot of methods for processing herbs. These methods include but are not limited to: discarding miscellaneous substances to make the herbs clean: cutting and /or breaking into small pieces, dissolving the effective components into a liquid substance, stir-frying, steaming, quenching, fermenting, etc. In addition to these relatively self-explanatory processing methods there are a few special methods that deserve explanation.
An introduction to some special methods
Stir-fried with liquid adjuvants. During stir-frying, the herbs gradually fully permeate into the liquid adjuvants. When Zi Yuan (Rodix Asteris) or Kuan Dong Hua (Radix Farfarae) are stir-fried with liquid honey the result formula is more effective at soothing the lung and relieving coughs. Wine-fried Chuan Xiong (Rhizoma Ligustici Chuanxiong) has a significant effect on activating the blood circulation and vinegar-fried Yan Hu Sou (Rhizoma Corydalis) exerts more remarkable effect for relieving pain than this herb in its unprocessed form.
Steaming. Steaming is a method of processing raw herbs by putting them in a steamer to heat them suspended over boiling water. He Shou Wu (Radix Polygoni Multiflori) originally, in its unsteamed form, is used to relax the bowels. When it has been steamed repeatedly the herbs property changes and it is used to invigorate the liver and kidney and replenish vital essence and blood. Sometimes multiple processing methods are used to achieve specific therapeutic effects. For example, the purging effect of Da Huang (Radix et Rhizoma Rhei) is reduced by steaming, after the herb has been stir-fried and mixed with wine.
Parching. In parching the herb is heated until the surface becomes burnt, like charcoal. Some herbs like Da Huang (Radix et Rhizoma Rhei), Zhong Lu (Petiolus Trachycarpi), Ou Jie (Lotus Root), Pu Huang (Typha angustifolia), Xie Yu (Human Hair), Ai Ye (Artemisia argyi) etc. could be parched or stir-fried together until charcoal they are like charcoal for the medicinal purpose of stopping bleeding.
Germinating or sprouting. Dao Ya (rice sprouts) and Gu Ya (millet sprouts) are germinated from rice or millet, and used for improving digestion.
Fermenting. Dan Dou Chi (Fermented soya bean) is used for treating the flu or common cold.
Frosting or chilling until frosted. Watermelon frost is the best product for treating throat infection.
Herb processing is an ancient technology of TCM in China with almost 2000 years of history. Modern research has shown that the properties of herbal ingredients are changed after processing, some are lost while some emerge. With the knowledge accumulated over centuries and present day technologies, it is possible to use various processing methods to make the best quality medicinal herbs.