Herbal medicine is part of human civilization. It has
been used in China for nearly 5000 y. One of the oldest
and most important documents is the Egyptian Ebers
papyrus (ca. 1550

), which includes more than 700

prescriptions using natural products such as caraway,
coriander, garlic, linseed, peppermint, figs, fennel, anise,
poppy, and castor oil [1]. Shen Nong’s Materia Medica
was compiled by ancient Chinese in about 200

, which

described the properties and usages of 365 types of
Chinese medicines in three categories. In ancient Greece
there was a guild of rhizomatists or root collectors, who
gathered, prepared, and sold medicinal plants. The
Greek botanist and physician, Dioscorides (

40–90),

compiled the first systematic description of 579 plants
and their 4700 medicinal uses and modes of action. His
work titled De Materia Medica was of central import-
ance to European medicine until the 17th century [1].
Ayurveda is the principal traditional medical system of

India, Pakistan, Nepal, and Sri Lanka, which has also
influenced medicine in Tibet, Burma, and Malaysia.

No doubt that synthetic drugs have played a vital

role in the enhancement of human living standards
during the past century; herbal medicine has regained
its momentum once again in recent years. Long-term
ailments cannot typically be cured by injection or
consumption of a single medicine. Instead of focusing
only on curing an illness, people are paying more
attention nowadays to improve the whole body im-
mune system so as to prevent the attack of diseases.
Besides their traditional pharmaceutical usage, herbs
have also become one of the important sources for
drug discovery and production. Herbal medicine
plays an important role in healthcare in many regions
of the world. The combined sales of herbal medicine
products in major markets around the world exceeded
US$12 bill ion in 1994,

Table 26.1

[2]. Accor ding to

the report from Herbal Medical Database Ltd., the
US market for herbal medicines has been estimated to

2006 by Taylor & Francis Group, LLC.

be worth US$ 58 billion in 1999 with an annu al
growth rate of 25%.

Ther e are more than 1000 types of herbs in use

around the world as medic ines, spices, flavors, etc. On
the basis of their biologi cal complex ity, they can be
classified as algae, fun gi, liverw orts and mosses, ferns
and fern allies, seed -bearing plants , and higher flower -
ing plan ts [3]. Dep ending on their physica l prop erties,
one can further classif y them as follows: sticky, aro-
matic, powder y, oily, and lust rous. This latter classi-
ficatio n determines the way the herb s are hand led.
The stick y he rbs usu ally contai n significa nt amou nt
of suga r, e.g., Radix Asparagi , Rhizoma Polygonati .
The a romatic herbs are known by their sp ecial scents .
Typical aromat ic herbs are: Herba Schizonepetae ,
Herba Menthae (also known as mint), Herba Elsholt-
ziae , and Rosae banksiae , etc. The powder y herbs
contai n large amo unts of star ch such as Rhizoma
Dioscoreae or rhizom e of c ommon yam. Radix Angel-
icae sinensis and Rhizoma Ligustici chuanxiong are two
oily herbs. For lust rous herbs, such as Radix Platycodi ,
Rhizoma Alismatis , and Astragalus membranaceus the
brightn ess of their surfaces is quite impor tant [4].

The quality of the he rbs depe nds very much on the

content s of active ingredi ents. It is known that heat-
ing or thermal drying, if not carried out prop erly, can
cause a signifi cant loss of the acti ve ingredi ents. The
drying methods describ ed below theref ore should be
adopted with care. For a specific herb sp ecies, its
traditi onal way of dr ying shou ld be analyze d caref ully
before any alternati ve methods are employ ed. The
compari son of diffe rent dr ying methods on the qual-
ity of herbs has to be carri ed out ba sed on physica l
and chemica l analyses. Var ious cou ntries hav e estab-
lished standar d testing methods for herb examin ation
with known indica tors for given specie s, for exampl e,
Species Systematization and Quality Evaluation of
Commonly Used Chinese Traditional Drugs [5] and
Handbook of Composition and Pharmacological Ac-
tion of Commonly Used Traditional Chinese Medicine
[6] are available in Chi na.

A large assort ment of drye rs can be used for dry-

ing herbs and medicinal plants. The reader is referred
to

Chapt er 1

of this handb ook for infor mation on

selection criteria for dryers.

26.2 DRYING OF HERBS AFTER

HARVESTING

26.2.1 H

ERBS IN

MALL

UANTITY

Herbs are very delicate plants. Their efficacy depends
on species, parts, planting location, harvest time, dry-
ing method, and storage. For a specific species, the
medicinal effect may derive from seeds, flowers, leaves,
stems, or roots, or all of these. Herbs were traditionally
harvested in small quantities from the mountains or
fields by individuals. Besides the active ingredients,
fresh plant material contains a high portion of water.
Leaves and flowers usually lose up to 85% of their
weight on drying. The fresh plant material is spread
out in thin layers (or in certain cases hung up in
bunches) and kept in a dry, well-ventilated place.
Tubers and roots take longer to dry than flowers
and leaves even though the former are often cut
up into pieces. The selection of proper drying tempera-
ture is vital. Too high a temperature may cause loss of
active ingredients. On the other hand, too low a tem-
perature may actually accelerate decomposition by
promoting enzyme activity within the plant itself
or even microbial attack, particularly for sugar-con-
taining substances.

Herbs are usually harvested when the flowers are

just coming into bloom, as they are then richest in
aromatic oils. As a guideline, one should pick herbs
just after the dew has gone and discard any yellow or
damaged herbs. Herbs should be handled with care
and only rinsed to remove obvious dust or soil. Herbs
may be dried in a ventilated room or in a barely warm
oven, leaving the oven door open. The temperature
should not exceed 348C. The following procedure is
suggested: lay the herbs on wire cooling racks covered
with muslin, cheesecloth, or nylon net. When dry, the
herbs are brittle and crumbly. Put the dried herbs
into storage jars, preferably of tinted glass, and
cover with a plastic screw cap. Appearance of signs
of condensation inside the jar, which implies that the
herbs are incompletely dried and hence should be
returned to the drying cupboard or oven. Long-
stemmed herbs may be dried by hanging them in a
warm, dry, airy place for a few days. They may be tied
in small bunches in a loose fashion. Cover the
bunches with dark paper if direct exposure to sunlight
may occur [3]. It should be pointed out that some
herbs are dried under direct sunshine, for example,

TABLE 26.1
Global Market for Herbal Medicine Products in 1994

Region

Annual Herbal Product Sales,

in Millions US$

European Union

6000

Rest of Europe

500

Asia

2300

Japan

2100

N. America

1500

2006 by Taylor & Francis Group, LLC.

Caulis Ephedrae, Radix Polygalae, Radix Astragali,
Radix Glycyrrhizae, Shiitake mushrooms, etc. Micro-
wave oven has been used recently for drying garden
herbs. For microwave drying, place a single layer of
herb leaves between double thickness of paper towels.
Dry them for 1–2 min on a medium to high setting (or
half of the power), depending on the thickness of the
leaves. Flip over and repeat for one more minute [7].
Pretests with grass are suggested if one is not familiar
with the microwave oven drying practice.

Catalytic Drying Technologies has introduced a

technology capable of significantly reducing the mois-
ture content of a wide range of agricultural products,
quickly and without causing product damage or gen-
erating regulated emissions. Tests have proven this
technology capable of reducing moisture content
from as high as 60% to levels between 3.4 and 4.4%.
The catalytic infrared system (burning gas without
flame) dries rice quickly and uniformly in a continu-
ous 3-h cycle. Low operating temperatures minimize
energy consumption; patented material handling and
agitation technology maximize efficient and uniform
drying [8]. The heat pump dryer has been investigated
and found to be useful in herb drying. It dehumidifies
the drying air, heats it, and leads it back for recir-
culation. This type of dryer can work at low air
temperature; thus color and active substances remain
intact. Another feature of the heat pump dryer is
its characteristic low energy consumption [9,10]. Sil-
ica sand drying can be used when the herbs are not
used as cooking recipes. Freeze drying can also
be used if it is important to retain the color of the
herbs and the active ingredients are highly heat-sen-
sitive. For a small quantity, simply place the fresh
herbs inside the freezer, which allows dehydration to
take place via sublimation. Freeze drying is an ex-
pensive process recommended only for high-value,
low-volume products.

26.2.2 D

RYING OF

EAVES

Tea is an ancient crop that has been cultivated for
thousands of years. Its exact origins have not been
confirmed by historians. There are many theories
about the discovery of tea. According to tradition,
tea was discovered by the Chinese Emperor, Shen
Nong in 3000

. The first records of tea date from

the 4th century

in China. Tea leaves are probably

one of the earliest and most consumed herbs. They
were initially found to have the property to counter-
act the poisonous effects derived from other herbs.
Nowadays, tea has become one of the everyday
drinks next to coffee and cocoa. The main tea produ-
cers are India, China, Sri Lanka, Kenya, Malawi, and
Indonesia. There are more than 1500 teas to choose
from, originating from more than 29 different coun-
tries [11]. The majority of the teas can be classified as
green tea, oolong tea, and black tea. Each requires
a different process and hence a different drying sys-
tem is required. The quality of dried tea depends to
a great extent on the drying system and operating
conditions used.

26.2.2.1 Green Tea

Green tea is drunk mainly in China, Japan, and some
parts of South America. Figure 26.1 shows the pro-
cess of a typical green tea production before final
sorting and packaging [12]. The initial water content
of fresh tea leaves after plucking is around 75–78%
(wet basis) in spring and 65–70% (wet basis) in au-
tumn [13]. The withering process is accomplished by
laying the tea leaves on trays or racks in the shade at
25–308C for a few hours depending on how wet the
leaf is. This process prepares the tea leaves for rolling
without losing juice. Meanwhile, the water content
falls to about 50% (wet basis). The kill out process
can be achieved by pan frying, steaming, or baking.
This process is designed to arrest the enzymatic reac-
tion, oxidation in particular. Pan drying usually em-
ploys a wok at a surface temperature of 400–4708C
(preferably 430–4608C) to reduce the leaves’ moisture
content to 10–15%. The drying step starts with using
hot air at 110–1208C to evaporate water in a layer of
tea leaves about 20-mm thick. In practice, air tem-
perature up to 1508C can be used. It is recommended
to have the dried tea leaves tempered to prevent the
edges of leaves from ‘‘crisping.’’ Then the next drying
starts with the wok temperature at 150–1608C and
drying time of 30–40 min until moisture content
reaches about 20%. Afterwards, the wok surface tem-
perature is reduced to 80–1008C and drying continues
for 60–90 min to have the moisture content of 9–10%.
Finally, the wok surface temperature is dropped to

Plucking

Sorting and

cleaning

Killing-out

Withering

Rolling

Drying

FIGURE 26.1 Production of green tea.

2006 by Taylor & Francis Group, LLC.

608C and drying carried out for 60–90 min until the
final moisture content of 4–5% is reached [13].

26.2.2.2 Oolong Tea

The process of oolong tea production is shown in
Figure 26.2. The freshly plucked shoots from Cam-
ellia sinensis are spread out thinly over a cleared area
of flat ground, which is usually covered with a mat or
a towel to keep leaves from contact with the earth.
The shoots are wilted in air under the sun for 30–60
min, depending on the temperature. The leaves are
then taken indoors to wither further at ambient tem-
perature for a few hours. This withering process can
also be assisted by heated air at <408C to shorten the
process time. During this process, the leaves are gen-
tly agitated by hand every hour. This process causes
the edges of the leaves to turn red [14]. During this
process, there is about 20% decrease in moisture con-
tent of the tea leaves. This step is accompanied by
‘‘fermentation’’ or curing to produce the unique
aroma and color found in oolong teas. To arrest
the enzymatic reaction so as to stop the leaves from
getting dark, the leaves are dried for 5–7 min at a
temperature slightly lower than that required for
‘‘killing-out’’ in green tea production. Afterwards,
the tea leaves are dried in a few steps in heated air
with rolling in between the drying steps. The first hot
air drying in conveyer belt or an oven is usually
achieved at a temperature around 1258C with the
depth of leaves 10–20 mm for 7–10 min. At the end
of this step the moisture content is about 40–45% (wet
basis). The second drying step is completed with air
temperature of 90–1008C for another 7–10 min until
the moisture content nearly reaches its equilibrium
level. A third drying step may be used at air tempera-
ture of 80–908C and a bed depth of 20–30 mm for 20
min. The second and third drying steps may be com-
bined using air temperature of 80–908C. The depth of
leaves can be a bit higher depending on the location of
the tea plants [13].

26.2.2.3 Black Tea

The process of black tea production is shown in
Figure 26.3. Tender young growth is picked by hand
from Camellia sinensis. Any surface water on
the leaves and shoots is allowed to dry on racks for
10–20 h to bring down the internal moisture content
so as to make the leaf more pliable for the next step.
The light, medium, and heavy withering can be
adopted with the moisture content decreases in 10,
15, 20% (wet basis), respectively. The selection of
degree of withering depends on the downstream
processes and the final product specification [13]. The
leaves are bruised to allow the fermentation process to
begin. Cutting is done at this point if necessary. The
rolling process will last until the leaves turn shining
dark red like a bright copper penny. The leaves are
allowed to ferment by placing thin layers on a tray in
a shady location for 2–3 days before drying [14]. If a
fermenter is used for the cut leaves, the temperature
should be controlled around 328C and time within 90
min. When moist air of 20–268C is blown through the
leaves, the fermentation time should be below 60 min
[13]. The drying can be accomplished in an oven set at
110–1208C for 12–16 min to obtain 18–25% water
content in the leaves of depth 15–20 mm. Further
drying is achieved by having oven temperature of
90–958C for another 12–16 min to the final moisture
content of 5–6% (wet basis). The higher temperature
step is necessary to stop the enzymatic fermentation
reaction and seal the flavors inside the leaves.

26.2.3 S

OME

YPICAL

RYERS FOR

EAVES

26.2.3.1 Multitray Oven

This type of dryer is usually designed for specialty tea
processing. It is an oven with about four layers of
trays. The drying surface area is 1–2 m

. Electrical

heating or heated air can be the source of drying
energy. The wet tea leaves are placed on the top layer
tray. The product is obtained in the bottom layer tray.
The moving of the trays is accomplished manually

Plucking

Sorting and

cleaning

Rolling or

shaking

Withering

Fermen-

tation

Frying and

drying

FIGURE 26.2 Production of oolong tea.

Plucking

Sorting and
cleaning

Rolling or
cutting

Withering

Fermen-
tation

Firing and
drying

FIGURE 26.3 Production of black tea.

2006 by Taylor & Francis Group, LLC.

usually from top to bot tom as drying pro ceeds. To
arrest the ferm entation quickly , he ated air can be
blown individu ally into each layer [13] .

26.2.3 .2 L ouver-Ty pe Oven

This dryer is similar to that of multit ray oven. The
main difference is that there are us ually six layers of
louver plates. The size of this dryer can v ary acco rd-
ing to the capacity req uirement. Again the wet leaves
are loaded at the top. As dry ing proceeds, the louvers
are flipped manual ly to turn the leaves to the ne xt
layer below . The flipping is done in alte rnative direc-
tions so a s to accomp lish a more uni form drying.
Heated air is blown from one side of the dryer. The
dried prod uct is colle cted at the bottom of the ov en.
This dr yer can also operate in the co ntinuous mo de.
The wet tea leaves are fed onto the continuous
moving louver plates. The louver plates make five
turns insi de the drying ch amber before sending out
the dried produ ct to the bottom . While moving , the
louvers are flipp ed accordi ng to the sch edule to ha ve a
more unifor m drying. This type of dryer c an have
a drying area of 50 m

. A schema tic diagra m of this

type of oven is shown in Figure 26.4 [13] .

26.2.3 .3 Conve yer Belt Dry er

Figure 26 .5 sho ws how a co nveyer dryer operate s.
Instead of louver plate s, a net belt is used in this
dryer. Supe rheate d steam is used as the drying med-
ium. The drying area can be 20 m

. It is go od for

drying small pieces of herbs and vegeta bles. Electr ical
heatin g can also be us ed as an auxiliary source of
thermal energy.

26.2.3 .4 Flui dized Be d Dryer

Figure 26.6

sho ws the schema tic layout of a fluidized

bed dryer [13]. This type of dryer is go od for drying
cut leaves in black tea produ ction. It can give a
unifor m drying in a relative ly sho rt period of tim e.
Mobile bed in co mbination wi th vibrating fluidized
bed may also be used for this purpo se. A fluid bed
dryer co nsists of a grid through whi ch hot a ir is
forced out. Fermen ted leaf wi th not too high mois -
ture content is suspe nded by the air stre ams, resul ting
in flui dization. The air also acts as a carrier of the
particles through the dryer, making the bed of leaves
move forward until the dried leaves are discharged .
To faci litate fluidiza tion of wet ferm ented leaf par-
ticles, the grid can be vibrat ed with half-ampl itude of
severa l millimete rs an d frequenci es in the range of 10–
20 Hz using metal spring s to make a v ibro-flu idized
bed dryer,

Figure 26.7

[15] . Thi s type of dryer for tea

leaves has be come very popular ov er the pa st three
decades. It is claimed to produce less fines and result
in gentler handling of the fragile leaves resulting in a
better quality product.

The fluidized bed dryer essentially consists of a

drying chamber, plenum chamber, dust collectors,
and flow control dampers. The drying chamber
normally consists of three drying zones and one cool-
ing zone. Fermented leaf is loaded on the grid plate of
the drying chamber. The top of the drying chamber
is closed and two sets of centrifugal exhaust fans

Wet tea leaves

Dried tea leaves

Wet tea leaves

(a)

(b)

FIGURE 26.4 Louver-type oven: (a) manual operation; (b) continuous.

Wet tea leaves

FIGURE 26.5 Conveyer belt dryer. (From Hu, J., Drying of
tea, in Modern Drying Technology, Eds. Y.K. Pan and X.Z.
Wang, Chemical Industry Press, Beijing, 1998, pp. 788–809.)

2006 by Taylor & Francis Group, LLC.

provided with cyclones—one for refiring and the other
for dust extraction. In the first zone of the dryer, the air
flowrate is the maximum to remove the very high mois-
ture content of the fermented leaf rapidly. As the
moisture content is reduced, the density of the particles
is also decreased. These lower moisture content leaves
tend to move away from the feed end and are replaced
by a new load of fermented leaf particles. When the tea
leaves are fully dried, they are expelled into a cooling
chamber where ambient air is introduced [15]. The
hybrid dryer consisting of tray dryer and fluidized
bed dryer may also be used to reduce the temperature
of the hot air in the fluidized bed and also to save on
energy consumption.

26.2.4 D

RYING OF

INSENG

OOTS

Ginseng is the most commonly used medicinal plant
in Asia. Recently, this ancient, cultivated plant has
been rediscovered in the Western world as a remedy
with numerous and diverse benefits. Traditionally,
ginseng was dug from the forest in the mountains. It

is a very delicate herb that usually takes 6 y or much
longer time to grow. In fact, high-quality roots should
be around 15 y or older. The harvested ginseng roots
are usually sun-dried [16].

Because of its economic values, ginseng roots are

now cultivated in China, Korea, North America, and
even Australia. The majority of ginseng root con-
sumed in the world today first needs to be dried.
The fresh root moisture content is around 72% (wet
basis). The dried ginseng has a moisture content of
approximately 8–12% (wet basis) [17]. Good quality
dried roots should have final moisture content
from 5.5 to 7.5% depending on the size of the roots
[18]. Drying is critical for quality ginseng root. Heat
damage or fungal development can occur from too
short or too long a drying process. Roots should be
sized and similar sizes dried together. The drying of
ginseng root can be achieved by placing them on wire
racks or bamboo baskets and leaving them under the
sun as done traditionally. It will take a few weeks for
the roots to dry. They are more often dried inside by
stacking the wire racks in a room with temperature

FIGURE 26.6 Fluidized bed dryer. (From Hu, J., Drying of tea, in Modern Drying Technology, Eds. Y.K. Pan and X.Z.
Wang, Chemical Industry Press, Beijing, 1998, pp. 788–809.)

FIGURE 26.7 Vibro-fluidized bed dryer. (From Hu, J., Drying of tea, in Modern Drying Technology, Eds. Y.K. Pan and
X.Z. Wang, Chemical Industry Press, Beijing, 1998, pp. 788–809.)

2006 by Taylor & Francis Group, LLC.

maintained around 388C. This drying process will
take about 2–3 weeks to complete. The dried product
will have a brittle exterior and creamy-white interior
[17]. The rough quality control is carried out by snap-
ping tests. A modified tobacco kiln dryer can be
used for large volumes of ginseng. Drying cabinets
can also be employed with the air circulation and
dehumidification systems equipped.

Temperature management is important in ginseng

drying. Too low a temperature will result in the green
coloring or molding, whereas too high a temperature
will give a product that is too hard (not easy to snap)
and of a brown color indicating the formation of
caramelized sugars. The danger of brown roots devel-
oping is greater toward the end of drying. It is not
recommended to accelerate the drying by increasing
the drying temperature at the last stage of drying.
Generally, drying is begun with temperatures at least
above 308C and temperatures below 388C are used
after root wilt. Using higher temperatures at the
beginning of the cycle will reduce the drying time
but it has to be ensured that the root temperatures
throughout the dryer are always within the safe limit.
Three or four thermometers should be placed inside
the drying shed to monitor the temperatures. The floor
temperature should also be monitored where the
value is the lowest. Heating of the shed can
be achieved by natural gas or electricity. Electric
heated walls have the advantage of not introducing
any odor from burning of natural gas.

Figure 26.8 shows a photo of a shed dryer for

ginseng roots. The drying history of different
sized ginseng roots is illustrated in Figure 26.9.

Large root refers usually to those of larger than
17 mm in diameter. The diameters of medium-sized
roots are from 12 to 17 mm. The small roots are those
of 7–12 mm in diameter. Any root with diameter
below 7 mm is classified as a fiber [18].

In a shed-type dryer the moisture laden, cooler air

will sink to the lower levels of the room. Thus, the
upper trays will tend to dry faster. To maintain a
uniform drying, either the upper trays are loaded
with large roots or the trays are rebuilt during the
course of drying to move the upper trays down and
lower trays up. During the first week of drying, the air
inside the room should be refreshed every 10–15 min
using an exhaust fan. The capacity of a shed dryer can
vary from 125 to 200 kg fresh root per sq. m. If higher

FIGURE 26.8 A shed dryer for ginseng roots. (From Brun, C.A., Ginseng, Cooperative Extension Program, Washington
State University, 2004.)

100

Moisture content, %(WB)

Days of drying

Value for long-term storage

Large
Medium
Small

FIGURE 26.9 Hypothetical drying curves of ginseng roots.

2006 by Taylor & Francis Group, LLC.

TABLE 26.2
List of Experimental Data of Some Herbs Dried by Convective Flow Heated Air

Name

Allowed

T, 8C

Actual

Maximum T, 8C

Ingredient

Loss, %

Maximum DT,

Air

Velocity, m=s

air

, 8C

Initial Moisture

Content,

kg Water=kg

Solids

Mean Drying

Rate,

g=kgmin

Cortex Mori Raicis

70–80

14.9

1.1

! 80

0.773

9.9

Fructus Aurantii seu Ponciri

50–60

1.4

0.7

! 75 ! 84 ! 68 ! 47

0.75

7.77

Herba Caricis phacotae

70–80

100

1.0

1.00

7.70

Herba Menthae

Ambient

68.5

100

1.3

0.80

6.8

Polyporus umbellatus

70–80

69.6

0.9

! 70 ! 54

0.88

6.76

Radix Trichosanthis

70–80

71.2

66.7

0.9

0.87

6.7

Cortex Moutan Radicis

50–60

2.7

1.0

0.60

6.5

Radix Paeoniae alba

70–80

1.1

0.70

6.5

Citrus reticulata

50–60

0.5

! 74 ! 26

0.28

6.1

Curcumae aromaticae

70–80

61.8

0.9

0.90

5.42

Astragalus membranaceus

70–80

0.8

! 70 ! 30

0.53

5.36

Cortex Magnoliae Officinalis

70–80

2.8

0.5

! 76 ! 70

1.03

5.22

Atractylodes macrocephala

70–80

2.8

0.5

! 70 ! 88

0.74

4.77

Cortex Phellodendri

70–80

49.1

17.4

1.2

0.40

4.6

Radix Platycodi

70–80

33.6

0.8

! 74 ! 68

0.29

4.5

Rhizoma Ligustici chuanxiong

50–60

0.8

! 50

0.923

4.5

Semen Arecae

70–80

0.5

1.3

! 70 ! 68

0.80

4.4

Radix Saposhnikoviae divaricatae

70–80

41.3

0.8

! 72 ! 66 ! 69 ! 50

0.34

4.3

Radix Glycyrrhizae

50–60

24.2

1.0

! 50 ! 45

0.44

4.09

Rhizoma Dioscoreae

70–80

69.8

16.6

0.7

0.81

4.14

Rheum Officiale

70–80

70.2

0.95

! 80 ! 53 ! 62

1.12

3.86

Radix Salviae

70–80

73.4

33.7

0.8

! 67 ! 62 ! 40

0.64

3.78

Radix Angelicae sinensis

50–60

29.1

1.0

! 59.8

0.75

3.77

Caulis Lonicerae

28.6

1.2

0.72

3.72

Atractylodes chinensis

50–60

49.9

0.8

0.356

3.69

Radix Isatidis

70–80

43.9

59.2

0.8

! 59 ! 56

0.29

3.1

Rehmannia glutinosa

50–60

11.4

0.92

! 71 ! 50 ! 60

1.08

2.74

ß
2006

by
Taylor

&
Francis

Group,

LLC.

loading rates are req uired, a better-cont rolled dry ing
room should be used.

Ele ctrohydr odynami c (EHD ) drying has been

report ed to work well for drying of root or sliced
root material s [19]. This techni que employ s high volt-
age DC and sharp cathode to generat e a corona to
accele rate the air movem ent close to the surfa ce of the
wet mate rial [20]. Bec ause this drying techni que re-
quires only slightly heated a ir for drying, it g ives very
high qua lity of dried mate rial. It is claimed as high
quality as freez e dried mate rials are obtaine d [21,22].
The econ omics of this novel drying process are not
clear as yet. For add itional detai ls, the reader may
refer other sections of this handb ook.

26.3 DRYING OF HERBAL MEDICINES

IN SMALL PIECES

Before the herbs can be used as herbal medic ines, fur-
ther treat ment is necessa ry. The dried herbs are usually
collected by a herbal pha rmace utical compan y where
they are was hed or rewett ed, cut, dried, and packaged
for sale. The rewett ing step is necessa ry to prepa re the
herbs for the cutting pro cess. Dryi ng is obv iously very
impor tant in smal l pieces herbal medicine process ing.

Table 26.2

lis ts the effe ct of convecti ve air drying on 27

types of herbs in smal l pieces , whi ch were placed on a
screen as heated air was blow n throu gh [23] . The dry ing
chamber used in these tests was 1.03 m

0.85 m

0.85 m in cross-sect ion. The weight loss of the material
was obtaine d from the reading s of an elect ronic bal-
ance. The dep ths of the beds of herbs were abo ut 30
mm. Nine tempe ratur es wer e mon itored in the fixed
bed of the herb pieces located at the center planes of the
rectan gular box . The maximum tempe ratur e in the
material and also the maxi mum tempe ratur e difference
in the mate rials are lis ted. Most of the drying was

condu cted over 90 min with the final mois ture
content of 0.08 kg water =kg solid s. The initial load of
the wet mate rial was about 400 g. The loss of active
ingredie nts can be quite high even though the
operatio n was co nducted at a temperatur e supposed
to be safe for these herbs [23] . More experi ments
by these au thors show that neithe r the air flowra te
nor the initial mois ture co ntent affect the quality
of dried he rb pieces . The qua lity of the dried herbs
depend s on the drying technol ogy and dry ing con -
ditions with tempe rature being a key parame ter to
control . It is antic ipated that for some herbs the cur-
rently listed values of a llowed tempe ratur e are simp ly
too high.

In order to maint ain a high drying rate an d a

low temperatur e of herb pieces , it is suggeste d to use
staged drying with variation of tempe ratur es of
heated air. For exampl e, in drying of 400 g of Radix
Glycyrrhizae from 0 .44 to 0.08 kg water =kg soli ds,
it took 70, 61, 48, and 55 min, respect ively, at tem-
peratur es of 40, 50, 70, an d (30

! 77 ! 60) 8C. For the

staged drying, the he ating from 30 to 77 8 C takes 28
min a nd the cooling to 60 8C takes about 27 min.
Table 26.3 g ives the temperatur e varia tion within
the materials. The depth of the fixed bed is also a
parameter to consider as demonstrated in the drying
of Cortex Mori Raicis. When the bed depth is in-
creased from 25 to 50 mm, the drying time is 2.7 times
longer and within the material, the maximum temp-
erature differences increased from 10 to 188C at a
drying temperature of 668C [23]. The optimal depth
for the experimental facilities described previously is
about 30 mm.

When infrared drying is used, the loss of active

ingredients is even higher for some herbs as shown
in

Table 26.4

[23]. In this drying experi ment, the

IR radiates sideways toward the fixed bed of herb
pieces. The depth of the bed is 30 mm. The initial

TABLE 26.3
The Experimental Data of Drying of Radix Glycyrrhizae

Temperature, 8C

Drying Rate, g=kgmin

Drying Time,

min

Heated

Air

Maximum at the

Bottom Surface

Maximum Difference

between Top and Bottom

Maximum

Average

33.5

7.8

10.5

5.6

11.5

6.2

12.4

8.6

! 77 ! 60

7.6

10.0

6.9

Air flow velocity

¼ 1 m=s, initial moisture content ¼ 0.44, final moisture content ¼ 0.08, depth of bed ¼ 30 mm, convective flow of heated

air drying.

2006 by Taylor & Francis Group, LLC.

mass of the wet mate rial is about 400 g. It is interest ing
to find also that some herbs remai n acti ve even though
drying was carri ed out a tempe rature exceed ing the
allowed values such as Polyporus umbellatus , Radix
Trichosanthis , Radix Glycyrrhizae , Rhizoma Ligustici
chuanxiong , etc. A compari son of the ingredi ent losse s
of the herbs dried by he ated air an d IR is given in

Table

26.5

. Bes ides the mate rial tempe ratur e, the way in

which the heat is supplied an d the mois ture is taken
away from the drying ch amber definite ly plays a role in
the quality of the dried he rbs. W hen infr ared drying is
combined with vibro-flu idized bed, Figure 26 .10, the
drying rate as well as the quality of the dried pro duct is
impro ved signi ficantl y [23]. Tabl e 26.5 lists 27 herbs.

For infor mation of herbs and their active ingredi ents,
readers are refer red to an on-lin e reference [24] .

The typical dryers found in drying of he rbs in

small pieces are oven , drying house, tunnel dryer,
vacuum dryer, and fluidized bed dryer. The descrip -
tions of these dryers can be found in the other chap -
ters of this handb ook [23,25].

26.4 CONCLUSIONS

Herb drying includes drying after harvest and drying
before processing. The drying after harvest usually
involves small volumes, thus the household equipment
can also be used. Either heated air or ambient drying

TABLE 26.4
The Experimental Data of Infrared Drying of Herbs

Name

Temperature, 8C

Active Ingredients

Tested=Method

Loss, %

Allowed

Actual

Heating Plate

Cortex Mori Raicis

292

Water extracts=standard

12.3

Fructus Aurantii seu Ponciri

279

! 212, K

¼ 0.76

Synephrine=HPLC

9.5

Herba Caricis phacotae

300

Phenylethyl alcohol=HPLC

100

Herba Menthae

Ambient

200

! 150, K

¼ 0.28

Menthol=GC

100

Polyporus umbellatus

293

! 229, K

¼ 0.13

Polyporus umbellatus

polysaccharides=UV

6.0

Radix Trichosanthis

386

Trichosanthin=UV

27.8

Cortex Moutan Radicis

282

! 175, K

¼ 0.74

Paeonol=HPLC

Radix Paeoniae alba

289

! 250, K

¼ 0.31

Albiflorin=HPLC

Citrus reticulata

275

! 130 ! 62,

¼ K

¼ 0.05

Hesperidin=HPLC

40.0

Curcumae aromaticae

88.9

280

Camphor=GC

39.3

Astragalus membranaceus

278

Water extracts=standard

17.6

Cortex Magnoliae Officinalis

72.6

295

Magnolol=GC

12.4

Atractylodes macrocephala

88.9

360

Water solubles=UV

11.7

Cortex Phellodendri

360

Berberine=HPLC

17.8

Radix Platycodi

387

Platycodoside=standard

28.6

Rhizoma Ligustici chuanxiong

374

! 219, K

¼ 0.81

Water extracts=standard

3.8

Semen Arecae

351

! 220 ! 170,

¼ K

¼ 0.23

Arecolime=standard

22.7

Radix Saposhnikoviae divaricatae

79.4

377

Mannitol=GC

65.9

Radix Glycyrrhizae

386

Glycyrrhizic acid=HPLC

17.9

Rhizoma Dioscoreae

296

! 241, K

¼ 0.33

Allantion=UV

10.25

Rheum Officiale

278

! 248 ! 217,

¼ K

¼ 0.22

Rhammoside=HPLC

Radix Salviae

281

! 264, K

¼ 0.71

Water extracts=standard

11.9

Radix Angelicae sinensis

338

! 286 ! 243,

¼ K

¼ 0.13

Ferulic acid=HPLC

55.6

Caulis Lonicerae

79.5

360

Chlorogenic acid=HPLC

Atractylodes chinensis

388

! 275, K

¼ 0.55

Alcohol extracts=GC

Radix Isatidis

77.7

360

Indirubin=UV

38.3

Rehmannia glutinosa

370

! 300, K

¼ 0.89

Water extracts=standard

0.08

¼ heating time at T=total drying time.

2006 by Taylor & Francis Group, LLC.

can be used. Freeze drying, microwave drying, or silica
sand drying can be used depending on the value and
sensitivity of the herb. For large quantity of herbs,
such as tea leaves or ginseng, drying requires indus-
trial-scale operation. The quality of the dried products
is important to control and thus governs the drying
conditions. For the drying of small pieces of herb
medicines, temperature control is important in retain-
ing the active ingredients. The selection of drying tech-
niques is also important in affecting the quality of the
dried herbs. Uniform drying of the small herb pieces
can give better quality of the products. The reader
may refer to other chapters of this handbook for an
in-depth discussion of industrial-scale drying e.g.,
fluidized bed, freeze drying, microwave drying, etc.

ACKNOWLEDGMENT

The authors are grateful for the financial support
of HK SAR Government from RGC600704 and
HKUST6038=00P.

TABLE 26.5
Comparison of Ingredient Loss between Heated Air and IR Drying

Name

Actual Maximum T, 8C

Ingredient Loss, %

Heated Air

Heated

Cortex Mori Raicis

14.9

12.3

Fructus Aurantii seu Ponciri

1.4

9.5

Herba Caricis phacotae

100

Herba Menthae

68.5

100

Polyporus umbellatus

69.6

6.0

Radix Trichosanthis

71.2

66.7

27.8

Cortex Moutan Radicis

2.7

Radix Paeoniae alba

Citrus reticulata

40.0

Curcumae aromaticae

88.9

61.8

39.3

Astragalus membranaceus

17.6

Cortex Magnoliae Officinalis

72.6

2.8

12.4

Atractylodes macrocephala

88.9

2.8

11.7

Cortex Phellodendri

49.1

17.4

17.8

Radix Platycodi

33.6

28.6

Rhizoma Ligustici chuanxiong

3.8

Semen Arecae

0.5

22.7

Radix Saposhnikoviae divaricatae

79.4

41.3

65.9

Radix Glycyrrhizae

24.2

17.9

Rhizoma Dioscoreae

69.8

16.6

10.25

Rheum Officiale

70.2

Radix Salviae

73.4

33.7

11.9

Radix Angelicae sinensis

29.1

55.6

Caulis Lonicerae

79.5

28.6

Atractylodes chinensis

49.9

Radix Isatidis

43.9

77.7

59.2

38.3

Rehmannia glutinosa

11.4

0.08

Wet

pieces

Dried

pieces

Heated air

Exit air

Infrared source

FIGURE 26.10 Vibro-fluidized bed dryer with IR heating.
(From Chu, Z.D., Drying of small pieces of Chinese medi-
cine, in Modern Drying Technology, Eds. Y.K. Pan and X.Z.
Wang, Chemical Industry Press, Beijing, 1998, pp. 810–841.)

2006 by Taylor & Francis Group, LLC.

REFERENCES

1. Lipp, F.J., Herbalism—the heeling power of plant:

regional translations, in Remedies & Recipes , Duncan
Baird Publishers, London, 1996.

2. Wang, D.I.C., Leung, J.C., Wu, I.-C., and Cao, N.,

Biotechnology and Hong Kong, in Made by Hong
Kong , S. Berger & R.K. Lester, Oxford University
Press, 1997.

3. Stuart, M., The Encyclopedia of Herbs and Herbalism ,

Orbis Publishing, London, 1979.

4. Ye, D.J., Zhang, S.C., and Chen, Q., Chinese Medicine

Preparation, Shanghai Science & Technology Publish-
ing, 2000 (in Chinese).

5. Lou, Z.-C. and Qin, B., Species Systematization and Qual-

ity Evaluation of Commonly Used Chinese Traditional
Drugs , Beijing Medical University & China Xiehe Med-
i c a l U n iv e r si ty J o in t P ub li sh in g, 1 9 94 ( i n C hi ne s e) .

6. Huang, T.K., Handbook of Composition and Pharmaco-

logical Action of Commonly Used Traditional Chinese
Medicine , China Medico-Pharmaceutical Science and
Technology Publishing House, 1994 (in Chinese).

7. Blose, N. Herb Drying Handbook: Includes Complete

Microwave Drying Instructions , Sterling Publishing
Co. Inc., New York, 2001.

8. Catalytic Drying Technologies, 20th and Sycamore,

Independence, IN, KS. 67301,

http: == www.catalytic

drying.com =company_profile.htm

9 . Universal Drying Locker T D-60, ThermoDynamic ,

http: == ww w. t hermo -dm. si=en =dryi ng_of_fruits.php

, 2004.

10. Chua, K.J., Chou, S.K., Ho, J.C., and Hawlader

M.N.A., Heat pump drying: recent developments and
future trends, Drying Techn ., 20(8): 1579–1610, 2002.

11. Crawford, H., The Chemistry of Tea, University of Bristol,

200 3.

http: == www.chem.bris.ac. u k=webprojects2 001=

cra w fo rd =intro.html

12. Tillberg, M., The Way of Tea, Tea Processing,

http: == tea.hypermart.net =teapage.html

, 2004.

13. Hu, J., Drying of tea, in Modern Drying Technology ,

Eds. Y.K. Pan and X.Z. Wang, Chemical Industry
Press, Beijing, 1998, pp. 788–809.

14. Live Herb Nursery, The Tea Plant Place, Processing

Tea,

http: == liveherbnursery.com =index.htm

, 2004.

15. Tea Research Association, Tocklai Experimental

Station, Tea Manufacture—Drying,

http: == www. tock-

lai.org=manufacture =drying.htm

, 2004.

16. Prinzenberg, E.D., Ginseng—Stay Young & Vital ,

Sterling Publishing Co., Inc., New York, 1999.

17. Brun, C.A., Ginseng, Cooperative Extension Program,

Washington State University, 2004.

18. Van Dalfsen, B., 1998, Ginseng Dryer Operation, Farm

Mechanization Fact Sheet, Ministry of Agriculture,
Food and Fisheries, British Columbia, Canada, Order
No. 280.380–1, 1998.

19. Hashinaga, F., Bajgai, T.R., Isobe, S., and Barthakur

N.N., Electrohydrodynamic (EHD) drying of apple
slices, Drying Techn ., 17(3): 479–496, 1999.

20. Lai, F.C. and Lai, K.-W., EHD—Enhanced drying

with wire electrode, Drying Techn ., 20(7): 1393–1405,
2002.

21. Chen, G . a nd Mujumdar , A. S., Appl icat ion of e lec-

trical fiel ds i n de watering an d drying. Dev. Chem. Eng.
Miner. Process.—Australas. Res. J., 1 0( 3 =4 ) : 4 29 – 44 2 ,
20 0 2.

22. Liang, Y.Z., Study of the Technologies of Electrostatics

Drying, Proceedings of the 7th National Drying Sympo-
sium , Jinan, China, 1999, pp. 343–348.

23. Chu, Z.D., Drying of small pieces of Chinese medicine,

in Modern Drying Technology , Eds. Y.K. Pan and
X.Z. Wang, Chemical Industry Press, Beijing, 1998,
pp. 810–841.

24. Chu, H.K., Traditional Chinese Medicine, 2004, in

Complementary and Alternative Healing University,

http: == alternativehealing.org

25. Zheng, P.Q., Formulation of Chinese Medicines, China

Pharmaceutical Technology Press, Beijing, 1998.

2006 by Taylor & Francis Group, LLC.

Document Outline

Table of Contents
Chapter 026: Drying of Herbal Medicines and Tea

Wyszukiwarka

Podobne podstrony:
Dr Gary L Glum Calling Of An Angel The True Story Of Rene Caisse And An Indian Herbal Medicine Cal
DISTILLING KNOWLEDGE new histories of science, technology, and medicine
Far infrared and microwave drying of peach (Jun Wang, Kuichuan Sheng)
Herbs Of The Field And Herbs Of The Garden In Byzantine Medicinal Pharmacy
Advantages and disadvantages of alternative medicine
Modeling and minimizing process time of combined convective and vacuum drying of mushrooms and parsl
022 Drying of Fish and Seafood
Characterization of microwave vacuum drying and hot air drying of mint leaves (Mentha cordifolia Opi
The Medicines and Dilutions of them habitually used by Hahnemann po angielsku
medicine and surgery of unusual pets 2008
Effect of vacuum microwave drying on selected mechanical and rheological properties of carrot
Microwave Drying of Parsley Modelling, Kinetics, and Energy Aspects
Effect of cocoa and tea intake on blood pressure
Drying kinetics and rehydration characteristics of microwave vacuum and convective hot air dried mus
Use of exponential, Page’s and diffusional models to simulate the drying kinetics of kiwi fruit
Thin layer modelling of the convective, microwave, microwave convective and microwave vacuum drying
DISTILLING KNOWLEDGE new histories of science, technology, and medicine
A comparative study on heat pump, microwave and freeze drying of fresh fruits

więcej podobnych podstron

026 Drying of Herbal Medicines and Tea

Document Outline