Processing of Herbal raw material

Processing of Herbal raw material

Processing of Herbal raw material

       Primary  processing

       Secondary Processing


At the end of this lecture, student will be able to

       Discuss the processing of herbal raw material

Primary processing:

     Harvested/collected medicinal plants and/or their parts undergo a series of good practice post-harvest (and post-collection) processing procedures

Ø  Garbling

Ø  Washing

Ø  Blanching

Ø   Drying


Ø  Garbling serves as the first step to ensure the purity and cleanness of the medicinal plant materials.

Ø  All extraneous and unwanted matters including dirt (e.g. soil, dust, mud,), impurities (e.g. insects, rotten tissues), and residual non-medicinal parts must be separated from the medicinal part(s).

Ø  The process may involve, depending on the plant material, procedures such as removing dirt and foreign substances, discarding damaged parts, peeling(to separate unwanted plant parts from the medicinal plant parts such as removing unwanted root bark from the roots or collecting stem bark from the stem)


Ø  After sorting, the medicinal plant materials should be cleaned well to remove remaining soil, dirt, dust, and other unwanted matters from the surface, especially roots, rhizomes and tubers, are commonly washed with clean water, dried soon after harvest/collection

Ø  During the washing process, scraping and brushing may be necessary. It is generally recommended not to soak the medicinal plant materials in water for an unnecessarily long period of time

Ø  Change water frequently as required


Ø  Blanching process in which they are put into boiling water for a brief period of time without being fully cooked

Ø  Which improves storage life of the processed materials by gelatinizing the starch and preventing mould/insect contamination, and facilitating further processing


Ø  Unless used in the fresh state, the raw medicinal plant materials are to be dried after being sorted and washed

Ø  In general, they must be dried as soon as possible to remove as much moisture as possible in order to ensure good keeping qualities and to reduce damage from mould and other microbial infestation

Ø  Drying will also avoid tissue deterioration and phytochemical alteration caused by the actions of enzymes and microbial organisms; and will also facilitate grinding and milling


Ø  Most medicinal plant materials can be dried in open-air under direct sunshine, provided the climate is suitable for such a practice

Ø  The duration of the drying process depends largely on the physical structure of the medicinal plant material and the weather condition

Ø  In the case of natural drying in the open air, medicinal plant materials should be spread out in thin layers on drying frames and kept away from possible contaminations such as vehicle exhaust, heavy dusts, and rain, as well as protected from insects, rodents, birds and other pests

Shade Drying:

Ø  Some medicinal plant materials can be dried in the shade with or without artificial air flow to avoid direct exposure to strong sunlight

Ø  Drying process is slow, but it is preferred to maintain (or minimize loss of) colour of leaves and flowers

Ø   Low temperatures will also preserve most of the volatile and aromatic components from being evaporated

Artificial Drying:

Ø  Drying by artificial heat is more rapid than open-air drying and is often necessary on rainy days or in regions where the humidity is high.

Ø  For artificial-heat drying, the temperature, humidity and other conditions should be governed by the physical nature of the drug and the physical/chemical properties of its active ingredients.

Ø  Over-heating may lead to an excessive loss of the volatile components and/or decomposition of chemical ingredients. As much as possible, the temperature should be kept below 60°C.

Tray dryer

       Shelf dryer/cabinet or compartment dryer

       Essentially hot air oven

       Material spread in thin layer in trays

       Number of trays depends on the size of the oven

       Hot air of desired temperature is circulated

       Dried material is taken out, cooled and pulverized

Secondary Processing

Cutting, sectioning, and communition: When thoroughly dried, the herbal materials are processed by cutting and sectioning into convenient sizes and shapes for storage,

Ø  Where applicable, the herbal materials should be cut or sectioned into specific shapes or forms, or comminuted/pulverized into powder form according to common practice found in herbal medicines

Ageing/Sweating:  The aging process refers to storing the herbal materials for a period of time after being harvested or collected from the field prior to use.

Ø  It is generally done under the sun or in the shade for up to a year, depending on the specific herbal material. During the process of aging, excessive water is evaporated and enzymatic reactions may occur to alter the chemical composition of the herbal material.

Ø  For example, cascara sagrada bark should be aged for at least one year prior to use

Ø  A similar process known as sweating involves keeping the herbal materials at a temperature of 45-65°C with high humidity for an extended period of time, from one week to a couple of months, depending on the plant species

Baking/Roasting: It is a dry-heating procedure using indirect, diffused heat, where the herbal materials are put in a heating device, often embedded in bran or magnesium silicate (talc) powder to ensure even heating on the entire surface at an elevated temperature for a period of time.

Ø  Some herbal materials are wrapped in moistened papers during the roasting process. The exact temperature used and duration of baking/roasting vary from one herbal material to another.

Ø  Some are baked or roasted until the surface colour turns yellowish brown; some may be further heated until charred.


Ø  Fumigation by sulphur dioxide has been employed in post-harvest handling of some medicinal herbs for the purpose of preserving colour, improving fresh-looking appearance, bleaching, preventing the growth of insect and overcoming decays caused by moulds


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