Drying of Crude Plant drugs

Freshly collected plant drugs contain as much as 55 to 82 percent of water. Since the drugs are not used immediately after collection, this high percentage of water encourages enzymatic and other chemical reactions and growth of moulds and bacteria in them, which bring about many undesirable changes in their constituents. In order to prevent these changes and to ensure good keeping quality of the drugs in transport and storage, they are dried to remove most of their water content. Drying stabilizes the drugs by fixing their constituents and facilities grinding and milling as well as render the drug into a more convenient from for commercial handling.

Methods of drying:

Depending on the type of the drugs and their chemical constituents, plant drugs may be dried by any of the following two methods: (a) Drying in open air by natural heat, and (b) Drying ip.door by artificial heat.

(a) Open air dryirig by natural heat may. be done either in the sun or in the shade, depending on the material to be dried. Sun drying is l,}sed for those drugs whose constituents are not unfavourbale affected by the direct action of sunlight, Shade drying is employed for those drugs in which retention of the natural colour is desirable and whose constituents are adversely affected on exposure to direct sunlight.

In this method, the drug material is exposed to the atmosphere under direct sunlight or under natural or artificially erected· sheds. The material is spread in thin layers, and turned over occasionally to expose fresh surfaces to the natural heat and air movements. As mentioned above, it is preferable to dry drugs in the shade in order to maintain colour and prevent undue shrivelling and distortion. Evidently, the destruction of the active con$tituents is less jn shade drying than in drying by direct sunlight.

(b) Indoor drying by artificial heat is the most· commonly used method a drying plant drugs, particularly the fleshy ones. The obvious reason is that this method has the following two advantages over the open air. drying method; (i) it stops enzymatic action more rapidly, and (ii) it is less time consuming as the desired heat and air flow can be effectively controlled and manipulated. Drying by artificial heat is most useful for drying drugs like Digitalis in which the cardiac glycosides undergo rapid enzymatic hydrolysis as soon as the leaves are harvested. Thus this method is generally the most acceptable method when skillfully operated. It involves the use of various mechanical drying devices, similar to heating ovens. Generally, such a device or heating chamber consists of a closed space provided with a number of movable screen trays to hold the drug material. The trays are arranged in such a way that free circulation of the heated air can take place inside· the chamber. The source of heat is usually placed at the bottom of the device and is effectively controlled to maintain an efficient temperature for vapourising the moisture. The device is also provided with a proper ventilation system to remove the moisture-laden air at the time of saturation. If heat and ventilation are properly controlled, the .material dries to produce a thoroughly dried drug of maximum quality. In drying drugs by this method, the following general rules are followed:

Leaves, barks and woods are pread in thin layers in the screen trays and dried at a temperature of about 40° to 6Qo C. They are thoroughly exposed to the heated air by occasional stirring. Leaves and barks containing volatile principles are also dried by this method, but a much lower temperature is used to protect the volatile constituents.

Roots and rhizomes are first thoroughly washed and then spread on the screen trays after removing the excess water. Large fleshy roots (e.g. Belladonna) or rhizomes (e.g. Ginger, Rhuqarb) or corms (e.g;, Colchicum) arc usually split or sliced to facilitate drying. They are then dried in the same way as the leaves and barks.

Flowers require greater care when drying by artificial heat as they contain less thermostable constituents. They are usually dried at a very low heat and the exposure time for their drying is usually much less than that of other plant parts.

Dried plants drugs often re-absorb moisture quickly when exposed to air. They should therefore be properly stored to maintain the moisture content to the desired level so that they are not spoiled by absorbing excessive moisture from the atmosphere.


Garbling is an important process in the preparation of drugs for commercial market and should be carefully done for producing a quality drug. Garbling of a crude drug sample involves the removal of extraneous matters and added adulterants from it by suitable means to produce a clean and pure drug. The common extraneous matters in crude plant drugs include other parts of the same plant, same parts of other plants, same parts of other plants growing together, rotten, discoloured or dried plant parts, dirts, soil particles and accidental or added adulterants. Partial garbling can be done during or after collection, but a thorough garbling should be done after the drying process and before it is baled or packed. Garbling can be done manually by simple hand picking or by the use of some simple devices like bars of magnet for removing adhering iron particles, sieves for separating dirts and small pieces of the same or other parts of the plant, or by using currents of air to remove chuffy and other lighter substances present in the drug material. In garbling a leaf drug the excess amounts of stems, flowers or fruits and any dry or rotten leaf present should be removed by hand. A process of sifting may be utilized to remove the broken pieces of leaves from an entire leaf drug sample before baling. Excessive quantities of overground stems or stem bases and roots should be removed from rhizomes and tubers before or after drying. Adhering dirts and soil particles in underground drugs may be removed by washing the fresh simples or by sieving, sifting, brushing or shaking the dried material. Drugs, in which admixture of iron particles are suspected, may be garbled by passing magnet bars several times through the sample. All particles of iron will thus be removed. Garbling is absolutely essential for producing a clean drug sample and to minimize damage to the grinding machine and to the dies and punches of the tablet machine by which some of the powdered crude drugs may be compressed into tablets.


Some preliminary quality control measures should be adopted to most crude drugs before they are packed and sent to the commercial market. These measures ensure marketing of a good quality product to the advantage of the prospective buyers, who may also adopt some other quality control measures before or after buying the material. This preliminary evaluation also helps to elevate or maintain the good reputation of a crude drug selling company.

Quality control tests or evaluatory tests are applied to small samples of large consignments of drugs. However, the samples taken must be representative of the whole consignment. During the preparation o( a crude drug for commercial market the following simp~e tests may be employed: (i) Preliminary examination for the general appearance of the sample by using macroscopical and sensory characters: (ii) Determination of foreign organic matters by manually picking out the extraneous matters from the sample and finding out their proportional quantity; (iii) Determination of the amount of moisture present in the dried drug by a simple “loss on drying” method to ensure that the sample does not contain too much of moisture, and (iv) some quantitative chemical tests to determine the amount of the active principles in the sample.

This type of information supplied by the seller about a drug not only attracts more customers for the drug but also fetch good price. Thus it is desirable that some quality control measures are adopted in preparing drugs for the commercial market preferably before packaging.


In order to send the prepared crude drug to the commercial market it must be put in some convenient containers or packages. The principal aim of packaging should be to provide ample protection to the drug as well as to give economy of space. However, the choice or the type of package to be used depends on the nature of the crude drug, the extent of handling it may undergo and its final disposition. Drugs, which are traded in nearby markets and which do not involve transportation or much handling or storage, may be packaged loosely in temporary ordinary packages. But the drugs that undergo transportation, much handling and storage should be packed in waterproof and strong containers or packages in a very compact way. If this involves a leaf or herb material it should be baled with power balers into a solid com pact mass and covered by suitable strong waterproof covers. This type of packaging is ideal for drugs like Senna, Strarnonium and Belladonna.· Drugs susceptible to deterioration by re-absorption of moisture (e.g.,. Digitalis, Ergot) should be packed into moisture proof cans. Extracts, gums and resins should be shipped in barrels, tin lined boxes and tin cans or metallic containers. Cowhides and skins of other animals, waterproof or waxed papers, leather bags or even wooden and hardboard boxes may be used as packaging materials for crude drugs as long as the protection of the quality of the drug is guaranteed. The outfit of the packages should be convenient for easy handling in transportation and stacking in storehouses.

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