Herbs In Africa
procedures and apparatus required for extraction purposes are simple. Skills
required would be carpentry, and light engineering skills, such as metal
cutting, drilling, and welding.
When considering the economics of small scale processing plant, there are
four factors that need to be balanced.
~ The costs may be reduced by utilizing used
dairy or food processing equipment. The main cost is for welding
Operational Cost ~ Energy use is a prime cost. Unwanted heat loss
will add considerably to energy use, as will bad design. Faulty design
produces increased labor costs, e.g., difficult load/unload
3. Maintenance ~ Parts and fittings that are awkward and difficult
to clean will add considerably to labor costs.
4. Durability ~ Fragile parts such as sight glasses should have
adequate protection. Seals and breakable joints that have to be dismantled
should be of good quality. Stopcocks, taps and valves should be corrosion
Contamination problems may easily arise because of the nature of the
substances involved in the processing, from chemical action of one substance
on another, e.g., heavy metals leached from the equipment are in themselves
toxic contaminants, which may then trigger a further reaction in the
substance being operated on.
Great care should be taken in the selection of materials that will be in
contact with solvents or herb extracts. If using plastics or rubbers, then
ask the supplier for the specifications of use. Do not use glaze ware
unless you know what type of glaze it is.There are also several
physical factors that need to be considered, e.g.,
Strength and Weight ~ Will the equipment be fixed or portable? Will the
equipment be able to withstand any stresses placed upon it?
~ Parts that are in contact with liquids and
vapors must be resistant to corrosion. Metals that are prone to rust should
as far as possible be avoided.
Expansion and Conductivity ~ When mating materials, which are different,
remember that they will have differing thermal expansion rates. That
will produce stress or fatigue with an increased risk of fracture.
Distillation equipment and condensers should possess good thermal
Cleansing and Sterilizing
~ Smooth polished surfaces will simplify
cleaning and sterilizing and help in the prevention of the formation of heat
Two of the most commonly used materials for plant construction are copper
and stainless steel. If considering copper, then it is most important that
all linings in contact with the herbal materials, liquids or vapors,
must be tin plated. Copper is a heavy metal that can cause liver damage. (hepatoxic).
Stainless steel will meet all criteria. Costs may be kept to a minimum
by purchasing and modifying used vats, fittings and tubing.
When nickel is added to stainless steel in sufficient amounts the
crystal structure changes to "austenite". The basic composition of
austenitic stainless steels is 18% chromium and 8% nickel. Austenitic grades
are the most commonly used stainless steels accounting for more than 70% of
production, type 304 is the most commonly specified grade. A higher grade is
excellent corrosion resistance
excellent weldability (all processes)
excellent formability, fabricability and ductility
excellent cleanability, and hygiene characteristics
good high and excellent low temperature properties
non magnetic (if annealed)
hardenable by cold work only
Percolation is a method of extraction achieved by the downward displacement
of soluble extractive by a suitable solvent through a suitably comminuted
drug plant. The process is a combination of maceration and percolation
and is sometimes referred to as a process of "Macero-Percolation'. Not
all plant drugs are suitable for the process (see Section 11-21). There are
7 distinct operations involved, they are in order of operation;
The principles of size reduction are covered
in section 11-16. Remember if the particles are too fine a solid cake may
occur, this will effect the downward flow of menstruum and will most
certainly lead to the formation of 'dry pockets' within the body of the
material which will escape extraction. It the material is too coarse then
interstices are formed through which there is a speedy percolation of
menstruum which produces an incomplete extraction and will require
excessive volumes of menstruum to exhaust the marc.
Principles of Size Reduction
The methods of size reduction (comminution) and the classification of
particles obtained are covered later in the article. A major factor in
the solubility of a substance is the amount of surface area exposed to
The greater the exposed surface, the faster and more complete is its entry
into solution, e.g.
The cube has 6 sides each side is 100 cm2
-: area exposed is 6 x 100 cm2 = 600 cm2.
We slice the cube into 8 equal portions.
The surface area for each cube is
6x 25 cm2 = 150 cm2 -:- 8x 150 cm2 = 1200 cm2
we have doubled the surface area.
The degree of comminution required will also depend on the composition of
the crude drug e.g. is it hard or soft ?, is it thick or thin ? If the
drug is leaves or petals then it will be easily penetrated by the solvent,
therefore the degree of comminution need not be great, whereas hard and
woody substances will require a greater reduction in size. Some substances
such as aloes or gum resins need only be crushed, therefore it is a
matter of becoming familiar with the material being operated on. The
following categories will serve as a general guide.
or Crushed. Gums, resins and inspissated juices. Most seeds and
or Small Cut. Rinds, skins, pith, stalks.
This type of size reduction is of dubious value and is only officially used
for quassia which is a hard wood. From personal experience the tedium may be
avoided by pulverizing such substances.
Rhizomes, roots, barks, woods, corms. There are 5 official grades of
details may be found in Section 6-45. For extraction purposes we may ignore
the 80 and 120 mesh with the 25 and 45 mesh being most often used.
The final consideration for the degree of comminution needed is the
menstruum or solvent to be used for the extraction. Remember that our
solvents are water, alcohol or a combination, i.e., dilute alcohol.
tissue of crude drugs in the dried state will contain around 4 to 5%
moisture (see Section 4-17) if it has been properly conditioned, therefore
if water or a dilute alcohol is used as the menstruum it will penetrate and
spread rapidly through the plant tissue; whereas strong alcohol i.e.,
50% by volume or over in the initial stages will cause a shrinkage or
hardening of the tissue because the water is pulled to the surface thus
shrinking the interior. This phenomenon may be explained by the fact that
ethanol molecules have a hydrophilic tail.
Apparatus for Size Reduction and Particle Classification.
Classification by Sieve.
Classification by sieve, may be used directly for particle reduction if
using whole dried herb. Sieves are further used for size classification of
materials that have been subjected to other means of size reduction.
size reduction may be achieved by the use of a mortar or pestle or on a
larger scale, the same method that is used to produce mealie from dried
maize in a village situation.
For larger scale work a suitable ball mill may be constructed from scrap
parts. It may be powered by hand, pedal, or other motive force such as a
suitably geared lawn mower engine or the electric motor taken from a
discarded washing machine. The general principle is :
Alternatively an agricultural feed mill will also serve the purpose but it
will require an engine or electric motor to operate the apparatus. Size
reduction is achieved by fixed or swinging beater arms revolving at speed
within a chamber.
Scale Extraction Apparatus.
represents a typical piece of laboratory extraction ware. It will be
seen that the principle is simplicity itself. Larger scale apparatus may be
constructed from discarded milking equipment. 50 or 100 litre
containers would meet the needs of the larger cultivation. It is not
necessary for the extractor body to be tapered. However a domed bottom as
shown in the diagram would facilitate the efficient extraction of the herbal
Choosing an Appropriate Extraction Process.
considering a crude drug for extraction purposes thought must be given to
whether the drug is classified as 'organized' or 'unorganized' . If
the drug has no clearly defined cellular construction it is unorganized. The
maceration process is the only method suitable for unorganized drugs such as
gums, resins, oleo-resins etc. Such materials are unsuitable for
percolation because the residues would block the percolation process. The
same restriction will also apply to crude organized drugs that produce
large amounts of mucilage e.g. flax or psyllium seed. In other cases
if a drug for whatever reason cannot be reduced to a powder then it is
not suitable for a percolation process. Some drug materials e.g.
Garlic and squill are extremely hygroscopic and in the presence of
water tend to fuse into lumps which make them unsuitable for the
Tinctures from Unorganized Drugs.
is the only feasible method of producing a tincture from an unorganized drug
such as gum benzoin or propolis resin. Further information on the
exudates will be found in Sections 9-16, and 9-51 et seq. 9-57.
The marc from the exudates is usually slimy or gummy and may also
consist of various types of debris e.g. insect parts, fragments of
soil or plant parts. The gums are insoluble in alcohol while the resins or
oleo-resins will pass completely into solution. The gum and debris will sink
to the bottom of the maceration vessel. The separation of the
supernatant liquid is usually by simple decantation or if required by
filtration. There is no advantage to be gained by attempting to press the
marc because all of the soluble constituents have entered into
Imbibition. The word is derived from the Latin meaning
'to drink in'. The comminuted drug thoroughly moistened with a portion of
the menstruum. This is best done in a lidded container of a suitable size.
The moistened drug is allowed to stand for a period of four hours to allow
the drug to imbibe the menstruum and thereby swell to its maximum capacity.
The container used should be large enough to accommodate the expansion of
On completion of imbibition the drug should be passed through a number 10
sieve (Table 6-45A) to break up any lumps that may have formed. The drug is
then transferred to the percolation vessel in portions. Each portion
should be firmly packed but not so firmly that liquid is forced from
the drug but sufficient to exclude any air pockets.
4. Maceration. Open the stop cock on the bottom of the
percolator and pour in the menstruum in portions and allow to percolate
through the packed drug. If the menstruum drips through the stop cock in
less than 10 minutes, the drug is too loosely packed. If the first
drop takes 25 minutes or more then the drug is too tightly packed. If
all is well, then close the stop cock and pour in sufficient menstruum
to leave a layer 1 or 2 cm deep over the drug. Cover the percolator and
leave to macerate for 48 hours in a warm dark place at a temperature
not exceeding 25�C.
The Pharmageddon Herbal
equivalent of a 3 year certificated course in Western Herbology, Save
These articles have been published in
Science In Africa
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