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Cultivation and Processing of Chinese Herbs

Information about the cultivation and processing of Chinese herbs and the manufacturing of Chinese herbal products

Processing Herbs for Herbal Products

How Clean and Pure Are Chinese Herbs?

Impurities in All Herbal Products

Processing Herbs for Herbal Products

(source: U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition)

Dietary supplements from plant sources are sometimes referred to as "phytopharmaceuticals." They are produced from fresh, dried or otherwise preserved plants or parts of plants.

The active ingredients are usually not completely isolated but rather are obtained along with other naturally occurring components of the plant. (These other components are often believed to influence the efficacy of the active ingredient.)

Sometimes the active ingredients are concentrated, and undesirable substances such as chlorophyll, tannins, or resins, are removed (List and Schmidt, 1989). The following sections discuss the various stages of production of dietary supplements of plant origin.

Cultivation and Collection of Plant Materials:
Most of the plants used for dietary supplements or medicinal purposes are cultivated, that is, grown on farms. Some, however, may be collected from the wild (Wijesekera, 1991). The following section discusses both methods for obtaining botanicals or herbals.

Cultivation allows producers to have more control over quality and purity than does collecting plants from the wild. Cultivars (cultivated varieties) of a number of medicinal plant species have been developed to produce high yields of the desired constituents. Some plants that are grown commercially for medicinal purposes are propagated vegetatively. (This means that new plants are grown from cuttings of old plants. Plants grown in this way are genetically identical to the parent plant.) Some medicinal plants are grown from selectively bred hybrid seeds, while others are varieties of plants that are unchanged from their natural form (Wijesekera, 1991).

A number of medicinal plants are cultivated for use by the pharmaceutical industry. Some examples include yams, which are used in the production of steroids; foxglove, which is used for digitalis; belladona, which is used for atropine; and opium, which is used to make morphine. The following is a list of major, commercially cultivated medicinal plants, many of which are used in dietary supplements (Wijesekera, 1991):

Aconites Costus Ipecac Rauvolfia Aloe Datura Lemon grass Senna Anise Dill Liquorice Smilax Artemisia Dioscorea Male fern Squill Basil Duboisia Mints Strophanthus Belladonna Ephedra Opium poppy Sweet flag Buchu Ergot Papain Thyme Casara bark Foxglove Periwinkle Valerian Celery Gentians Podophyllum Vinca Chamomilla Ginseng Polygala Withania Cinchona Henbane Psyllium Colchicum Hydrastis Pyrethrum

A number of countries commercially cultivate and export substantial quantities of medicinal plants. These countries include China, India, Thailand, South Korea, Brazil, Mexico, Egypt, Indonesia, Nepal, the Philippines, and Kenya. Eastern European countries cultivate medicinal plants as well, but mostly for their own consumption (Wijesekera, 1991).

As for any agricultural crop, producers of medicinal plants must provide plants with adequate moisture and nutrients and must control pests and diseases. Pesticides must be used cautiously to reduce the risk of harmful residues on plants (List and Schmidt, 1989). Production of medicinal plants is generally labor intensive. In many cases, only the portions of the plant that contain the active ingredients -not the whole plant- are used. Sometimes harvesting involves picking leaves and flowers by hand (Hornok, 1992). In the future, tissue culture may be used for producing plant material (List and Schmidt, 1989).

Collection from the Wild:
Tropical forests are the source of a number of plants used for medicinal purposes. There are several disadvantages to collecting wild plants, however. This practice, along with deforestation, has caused some wild plant species to become endangered (Wijesekera, 1991).

Also, when plants are collected from the wild, there is a risk that they have been incorrectly identified (List and Schmidt, 1989). One advantage to using wild plants, however, is that they are unlikely to contain any pesticide residues (Wijesekera, 1991).

After the plants are harvested or gathered, they must be cleaned. Cleaning may involve screening, washing, peeling, or stripping leaves from stems. Any unnecessary parts are removed prior to drying to avoid wasting time and energy. Cleaning is often done by hand (Hornok, 1992).

In some cases, botanicals are used for extraction while fresh, but generally, they are dried first. The purpose of drying is to reduce the water content so that the plant can be stored. Most plants contain 60 to 80 percent moisture when harvested and must be dried to within 10 to 14 percent moisture before storage. Plants must be dried or processed as soon as possible after harvest because they begin to deteriorate immediately. Processing up to this point is generally done by the producer of the plants (Hornok, 1992). Plants can be dried naturally or by a number of artificial methods. The type of plant or plant part being used will determine the appropriate drying technique (List and Schmidt, 1989).

Natural Drying: A practice that has been used since ancient times is sun-drying in the field. Although this method requires no drying equipment and uses solar energy, it requires large amounts of space, and plants can be damaged by the weather. Sometimes plants are placed by hand on drying frames or stands, to be air-dried in barns or sheds. This method of drying is labor-intensive and can take several weeks. The exact length of time for adequate drying depends on temperature and humidity (Hornok, 1992).

Artificial Drying:
With the use of artificial dryers, drying time can be reduced to hours or minutes, and labor can also be greatly reduced. Fans that blow unheated air (cold-air drying) can reduce drying time to several days. Warm-air drying, which is the most widely used method for medicinal plants, uses a counter-current flow of warm air. There are several different types of systems for warm-air drying. One type is the plate chamber dryer, which blows warm air across plates on which plants have been placed. This method is useful for fragile flowers and leaves but requires large amounts of labor. Workers must load and unload the plants from the plates manually. The capacity of these dryers is relatively low, as well. Conveyor dryers are a commonly used type of warm-air dryer. Fresh plants travel on a conveyor belt through a counter-current flow of warm air. These dryers can operate continuously, require relatively little labor, and have high throughput. However, they require a large capital investment and have high energy requirements. The drying time required for conveyor dryers ranges from 2.5 to 6 hours, and the temperature of the drying air ranges from 40 to 80°C. Hot air dryers, which use very high temperatures (200 to 1,000°C) for very short periods (2 to 5 minutes) are not commonly used for drying medicinal plants (Hornok, 1992).

Packaging of Dried Plants: Once drying is complete, plants are packaged in preparation for shipping and further processing. Dried herbaceous plants are generally compressed into bales weighing from 60 to 100 kg (13 to 220 pounds), which are then sewn into fabric bags or wrapped in plastic. Materials that cannot be baled, such as roots and bark, are placed in sacks. Smaller bags may be used for dense materials such as dried fruits or seeds. Very fragile materials, such as flowers, are packaged in crates. Dried plant materials tend to be hygroscopic (readily absorbing moisture) and must be stored under controlled humidity. Highly hygroscopic materials are generally packed in plastic (Hornok, 1992).

Cleaning and Sorting: When the sacks or bales arrive at the processing facility, processors open the packages and clean the dried plants to remove as many impurities as possible. Sand is removed pneumatically and iron-containing metals are removed magnetically. Next, processors sort the plant pieces by size, since different end-uses require different particle sizes. For example, finely shredded material may be used for tea bags and somewhat less finely shredded material for loose teas or infusions, while coarsely shredded material may be sold directly to consumers or used for extraction. Particles that are already the desired size can go directly into storage to await further processing. Particles that are too big undergo additional grinding, cutting or shredding, and sieving. Various methods are used to reduce particle size including hammer action, pressure, friction, impact cutting, and shredding (List and Schmidt, 1989). Some plant materials are packaged and sold at this point without any additional processing. Some proceed through an extraction process, which the following section describes. Extraction: Extraction is a process whereby the desired constituents of a plant are removed using a solvent. The following section describes several methods used for preparing extracts, including organic solvent extraction, supercritical gas extraction, and steam distillation.

Organic Solvent Extraction: Organic solvent extraction is one process for separating the desired substance from plant material. As was previously mentioned, dried plants are usually used for extraction, although fresh plants are sometimes used. The plants are first ground and then thoroughly mixed with a solvent such as hexane, benzene, or toluene inside a tank. The choice of solvent depends on several factors including the characteristics of the constituents being extracted, cost, and environmental issues. If the end product will contain trace amounts of residual solvent, a nontoxic solvent must be used. Once the solvent dissolves the desired substances of the plant, it is called "miscella." The miscella is then separated from the plant material (Hornok, 1992). There are a number of techniques for solvent extraction, which include maceration, percolation, and countercurrent extraction. The following is a brief description of each.

Maceration: This method involves soaking and agitating the solvent and plant materials together. The solvent is then drained off. Remaining miscella is removed from the plant material through pressing or centrifuging. This method does not totally extract the active ingredients from the plant materials.

Percolation: With this method, the plant material is moistened with solvent and allowed to swell before being placed in one of a series of percolation chambers. The material is repeatedly rinsed with solvent until all the active ingredient has been removed. Solvent is reused until it is saturated. New solvent is used on plant material that is almost completely exhausted, and then re-used on subsequently less exhausted batches. This method is more effective at removing active ingredients than the maceration technique.

Countercurrent extraction: This is a highly effective process whereby solvent flows in the opposite direction to plant material. Unlike maceration and percolation, which are batch processes, this method is continuous. Screw extractors and carousel extractors are two types of equipment used for countercurrent extraction (Wijesekera, 1991).

Purification and Concentration of Miscella: Miscella that has been separated from the plant material generally contains some unwanted substances such as tannins, pigments, microbial contaminants, or residual solvent. Methods such as decanting, filtration, sedimentation, centrifuging, heating, adsorption, precipitation, and ion exchange are used to separate impurities from the miscella. Sometimes the miscella resulting from solvent extraction is used as the final dosage form. This is known as a "fluid extract" (List and Schmidt, 1989). The miscella is sometimes concentrated in order to increase the proportion of the desired substance. This is done through evaporation or vaporization. Solvent is generally recovered and reused (List and Schmidt, 1989). The degree of concentration depends on the desired end product. Equipment for concentrating the miscella may include descending film, thin layer or plate concentrators. Any method used to concentrate the miscella must avoid excessive heat because the active compounds may be subject to degradation (Wijesekera, 1991). Sometimes extracts are dried completely using vacuum freeze dryers, cabinet vacuum dryers, continuously operating drum or belt dryers, microwave ovens, or atomizers. The technique for drying depends on the stability of the product and the amount of moisture that must be removed. The resulting powdered extract is less subject to microbial contamination than are liquid extracts (Hornok, 1992).

Extraction with Supercritical Gases: This is a method for extracting active ingredients using gases. The plant material is placed in a vessel that is filled with a gas under controlled temperature and high pressure. The gas dissolves the active ingredients within the plant material, then passes into a separating chamber where both pressure and temperature are lower. The extract precipitates out and is removed through a valve at the bottom of the chamber. The gas is then reused. Gases suitable for supercritical extraction include carbon dioxide, nitrogen, methane, ethane, ethylene, nitrous oxide, sulfur dioxide, propane, propylene, ammonia, and sulfur hexafluoride. An advantage of supercritical extraction is that it can take place at low temperature, thus preserving the quality of temperature-sensitive components (List and Schmidt, 1989).

Steam Distillation: Steam distillation is another method for extracting active ingredients from medicinal plants. The plant material is loaded onto perforated plates inside a cylindrical tank or still, and steam is injected from below. The steam dissolves the desired substances in the plant, then enters a condenser where it is condensed back into a liquid. This condensate then passes into a flask, where the extract either rises to the top or settles to the bottom and is separated from the water. Distillation is complete when there is no more extract present in the condensate. The water may be reused, and the extract is purified through centrifuging and filtering (Hornok, 1992).

Other Minor Extraction Methods. Other minor methods for making extracts include cold pressing and the enfleurage process. Cold Pressing: Cold pressing is a process used to extract essential oils from citrus plants through pressing (Hornok, 1992). The enfleurage process is the same as the technique used to make perfume from flowers: purified fats are used to extract essential oils from plant parts. Plant material is spread onto sheets of purified fat, which dissolve the essential oils (List and Schmidt, 1989). Sometimes practitioners of herbal medicine prepare extracts for immediate use. These include aqueous extracts known as decoctions, infusions, or macerations. Plant material is mixed, agitated, and soaked in water to dissolve the active ingredients. Controlling microbial contamination can be difficult in aqueous extracts. Oily drug extracts, also called "medicinal oils," may be prepared by soaking or macerating the plant material in an oil such as almond, peanut, olive, poppy seed, apricot kernel, or peach kernel oil. Vinegar is sometimes used to extract active ingredients as well. Plant materials are soaked in acetic acid, and the vinegar is consumed as the final dosage form (List and Schmidt, 1989).

Controlling the Quality of Extracts: Once an extract has been produced by one of the methods mentioned above, producers can use a number of tests to evaluate the quality and purity of their product. First, they may examine the physical characteristics of the extract. This may include evaluating its appearance, pH, solubility, total solids content, ash content, and in the case of dried extracts, particle size. Next, they may analyze the components of the extract to be certain it contains the appropriate quantities of desired ingredients. Chromatography (including thin layer, column, high pressure liquid, and gas chromatography) may be used for this. Finally, they may test the extract for impurities such as residual solvents, herbicides, and pesticides and for microbial contamination (Wijesekera, 1991). Some extracts are labeled and sold as standardized extracts. According to industry sources, the desired constituents in standardized extracts are measured and are listed as a percentage of the total weight of the extract. For example, echinacosides are the desired compounds present in echinacea extract. A capsule containing 250 mg of echinacea extract standardized to 4 percent would contain 10 mg of echinacosides. In some cases, the desired constituent is a known active ingredient. In cases where the active ingredient has not been identified, another "marker " compound, or substance that is known to be present in the plant, may be measured for the purpose of standardization. Spectrophotometric testing and high pressure liquid chromatography may be used to measure standardized constituents (Standardized Extract Product Guide, 1997).


By Subhuti Dharmananda, Ph.D., Director, Institute for Traditional Medicine, Portland, Oregon

During the past few years, a number of disturbing reports have appeared that describe contamination of Chinese herbs and herb products. In some cases, the situation is incorrectly reported or exaggerated, but in others there are cautions that practitioners should take seriously.

Pesticides (Applied During the Cultivation of Herbs)

A large number of Chinese herbs are collected wild, and therefore, are not subjected to any pesticides. Some cultivated plants do not require the use of pesticides because they have natural resistance to pathogenic organisms and insects. However, some Chinese herbs are grown with pesticides. Most herb growers are sensitive to the issue of pesticide use and take adequate precautions to avoid contamination of the harvested materials.

Many herb cultivators in China cannot afford to purchase modern chemical fertilizers and pesticides and rely, instead, on natural materials and careful cultivation techniques.

Regulations have been published in China requiring cultivators to follow certain practices that minimize pesticide use and residues.

Still, some of the specific restrictions on pesticide use that are imposed in America. . .are not present in China. This means that some of the pesticides that are used in China on herbs are not permitted in the U.S. for those crops (even if permitted for other crops). A particular problem has been noted with ginseng cultivation. Fungicide materials are used at times, because the ginseng plant is highly susceptible to fungal rot, especially during its early growth period. Care is taken to avoid applying any chemicals close to time of harvest so that natural processes (e.g., heavy rains) have time to eliminate most of the fungicides prior to harvesting.

Nonetheless, fungicides and pesticides have been detected in some samples of ginseng and notoginseng (tien-chi ginseng).

Fumigants (Applied after the Harvest of Herbs)

Many people apparently believe that Chinese herbs are fumigated at the ports when they arrive in America. I have never been able to find any substantiation for this claim; all authorities (including U.S. Department of Agriculture and Food and Drug Administration) have thus far denied any such general action and there are no reported mechanisms for initiating such action. Evidence of live organisms, beyond anything normally expected, can result in rejection of the shipment. Chinese herbs imported into the U.S. generally have a very clean appearance, as anyone who has seen Chinese pharmacy materials may note. Sometimes, when large batches of herbs are stored in warehouses in China prior to being distributed to their final markets, if there is a delay in distributing them, fumigants might be used to assure that the entire supply is not endangered by a rapidly-multiplying insect pest.

However, China has effective herbal fumigants as well as chemical ones available for use. The majority of Western herbs, just like all Chinese herbs, are imported; they frequently come from South or Central America and Eastern Europe, and are subject to the same rules and regulations as Chinese herbs; these Western herbs might also be fumigated in their home country during storage. Fortunately, the high quality Chinese herbs destined for foreign markets, such as the U.S. and Europe, are items that are in high demand and thus have a high turn-over, with less likelihood of needing any such long-term storage.


It was reported, by Frontier Herbs Company, that several Chinese herbs have relatively high levels of sulfur. This is the result of a processing method whereby herbs are spread on screens, underneath which is some heated sulfur. The sulfur fumes waft through the herb material and leave some residue (which is intentional). These sulfur residues are sometimes referred to as sulfites, bringing images of sulfiting agents sprinkled on restaurant lettuce or added to finished wines. However, the sulfur compounds resulting from this method of preserving the herb quality are not known to cause reactions in sulfite-sensitive individuals (sulfur is one of the most prevalent elements in the human body, and is essential to all life). Treatment with sulfur is mostly carried out on those herbs that are moist (e.g., ophiopogon) or those that discolor significantly over time (e.g., atractylodes). Some importers specifically obtain herbs that have not been sulfur treated and will mention that in their literature. There may not be any health problems that can be associated with the sulfur processing as carried out in China, but those who are concerned now have a choice, at least for crude herb materials.

Irradiation (after Import)

Today, many of the herbs and spices sold in grocery stores are treated by ionizing radiation as a means of sterilization. Crude Chinese herbs are not subjected to this procedure, with one exception: certain animal materials, mainly deer antlers, are irradiated under direction of the U.S. Department of Agriculture, to assure that organisms that cause disease in animals are not carried into this country (the same requirements exist in other countries). This type of irradiation does not leave radioactive contaminants. Some manufacturers of finished products (e.g., extract powders or granules) may utilize gamma irradiation as a means of reducing bacteria counts on the finished products; this procedure does not result in any radioactive contamination.

Sterilizing Gases (Applied after Powdering)

Some Western herb companies routinely "sterilize" their herbs before putting them into capsules (the treatment substantially reduces the bacteria count to a level deemed acceptable). The treatment involves putting the herbs into an airtight chamber, introducing a gas, such as ethylene oxide, heating the chamber to about 180 degrees Fahrenheit for several hours, and then evacuating the gas and allowing the herbs to de-gas for another twenty-four hours. The same procedure is applied to Chinese herbs that are distributed by these companies. When herbs are so treated, there may be a small amount of ethylene-derived residue which arises mainly from interaction of the sterilizing gas with water in the herb materials. There is no evidence that such treatment of the herbs is necessary for any health purpose (see below). The crude Chinese herbs used for making most Chinese herb formulas for health professionals are not treated by this method.

Bacteria, Mold and Yeast

Herbs are generally free of harmful bacteria, but they do contain naturally occurring microorganisms... The bacteria that can cause food poisoning in relative small amounts, Salmonella, is not found in Chinese herb formulas; for example, in one series of tests, no Salmonella contamination was discovered in more than 25 random samples. Recent testing of oyster shells similarly showed freedom from this bacteria (oyster meat is frequently a source of it). Salmonella is found in certain animals, such as lizards, but the gecko lizard used in making certain Chinese herb formulas is baked to destroy any of this organism that might be present. E. coli, an indicator of animal fecal contamination, is rarely found in Chinese herbs, and in those rare cases the counts have been very low. Total coliform counts (which include several harmless organisms) in the Chinese herb tablets are generally less than 500 per gram; counts below 1,000 are considered low for natural materials.

Viruses (that May Be Present in Animal Products)

Assays have not been carried out to determine the presence of viruses in animal materials from China. A concern was raised by some American practitioners about the possibility of human viruses in placental material from China. The processing of human placenta before it is shipped to the West includes boiling followed by baking, and the material that arrives is very dry, making it highly unlikely to contain any organisms that might have been originally present. The materials are further heated and dried by the grinding process used for making powders (for pills); alternatively, it is sterilized by boiling when the material is used in making a decoction. Small amounts of any residual viable virus would be very unlikely to cause disease when consumed orally. Nonetheless, the FDA has recently restricted use of human placenta because of their general rules-regarding potential contamination-for use of human substances in medicine.

Heavy Metals

Reports that Chinese herb products were contaminated by heavy metals emerged in the late 1990s and included an extensive testing of patent remedies by the California Health Department, Food and Drug Branch, published in 1998. Two metals detected in several products, mercury and arsenic, are the result of intentional addition to herb formulas, following the belief that these compounds improve the effects of the formulas. The primary additives are cinnabar (contains mercury) and realgar (contains arsenic). Western manufacturers of Chinese herb formulas never add these compounds, so mercury and arsenic are not present in amounts higher than normally found in plants (below 3 parts per million). Lead contamination of Chinese herb formulas may occur either from intentional addition of lead compounds (rare, but sometimes done in Hong Kong) or by unintentional contamination (environmental contamination of the herb materials or factory contamination). Chinese herb formulas manufactured in the U.S. and other Western countries never have added lead compounds. The level of lead found in the imported herb materials used for manufacturing formulas is generally quite low, almost always meeting the World Health Organization standard of not more than 3 parts per million.

Western Drugs in Patent Herbs

Western drugs are present in some patent formulas made in China, and this is not always indicated on the label. A well-known case is a variety of Yin Chiao tablet ("superior quality-sugar coated") from Tianjin, which includes an analgesic and an antihistamine (it also has caffeine added). Many practitioners and consumers are not familiar with the ingredient labeling of herbs and drug ingredients, and therefore may not realize that a drug is present in a Chinese product sold in a Chinese herb shop. Although it is illegal to import such materials for sale in the U.S., they have found their way into several Chinatown shops.

Typical drug additives were antipyretics (e.g., aspirin and acetaminophen), antihistamines, and antibiotics. The products were not labeled to indicate that they contain drugs

Additives in Manufacturing

Many people prescribe Chinese herbs that have been processed to some extent beyond the minimal processing to produce "crude" pharmacy materials. Chinese pills may be made with honey or other binders, as well as have a coating of vegetable oil. Most cough syrups and herb extracts in liquid form (in vials) are made with sugar, honey, or both. Tablets are made with flow agents, binders, and coatings. Sugar-coated tablets and capsules made in China may have synthetic colors as aids to identification. Capsulated herbs contain flow agents and the capsule is made from animal gelatin (vegetarian capsules are rarely used and are made of the same materials used to coat tablets). Dried decoctions are often produced with a starch carrier (such as potato starch) or from the powdered herb dregs left over from the extraction procedure. For products made in the U.S., most manufacturers provide a list of items that are not used in the product which consumers may be concerned about (e.g., corn, soy, wheat, animal materials, etc.). Some manufacturers provide disclosure of all additives used in manufacturing. Typically, these involve various cellulose materials (fillers, disintegration aids, binders, coatings), magnesium stearate (flow agent), and various types of gums (binding agents). In most cases, all the additions to the basic herb material constitute less than 10% of the weight of the finished product (with the exception of products comprised of isolated active components, which may have a larger proportion of filler to control the dosage amount).

Incorrect Herb Material Provided

Another type of "contamination" is receiving an incorrect herb material; thus, the one that is not actually desired contaminates the finished product. In the case of Chinese medicine, herb substitution is a common practice, and whether or not an herb is "correct" or not may depend on certain expectations. When ordering Chinese herbs, there is a possibility that the material obtained will not be the one requested, and if the recipient is not familiar with the appearance of the proper material, then a wrong item may be used.

Labels on some packages of imported Chinese patents are sometimes deceptive. In some formulas, aconite is labeled as cyperus, and in a number of products, "ginseng" appears in the name of the product but not among the ingredients (it is substituted by codonopsis); a recent label for Wuchi Paifeng Wan does not show that black chicken is present, even though it is a major ingredient. Items said to contain musk, ox gallstone, rhino horn, pearl, or other expensive items may contain various substitutes; in the case of musk, the substitute may be a synthetic chemical (muscone). None of the Chinese patents tested by the U.S. Fish and Wildlife Department showed evidence of containing the endangered animal species, such as rhino horn or tiger bone, that were listed on their labels.

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