Cashew Nut Processing -
An Overview
Raw
cashew nut harvesting, handling and storage
Cashew
nut is hand picked and manually handled in various stages of operation -right
from picking at farm level to processing at factory level and up to storage and
transportation. To preserve the quality of harvested nuts, it is imperative
that proper safeguards are observed against natural and man-made
contaminations.
Improper
post-harvest handling and storage of nuts, such as high moisture, unsuitable
temperature and insect or mechanical damage can influence the incidence of
fungus that produces toxins like afflatoxin.
By
following proper method of drying, fungal infection can be avoided. After
drying (to about 8 to 10 % moisture level) the nut must be freed from any
adhering plant material. Shriveled and spoiled nuts, which are potential
sources of fungal infection, should be removed. Only healthy and matured nuts
should be kept for storage.
Quality
of Raw nut in harvesting, handling and storage can be ensured by:
1.
Proper Harvesting techniques - Only
matured nuts from fully-grown apple must be harvested.
2.
Proper Drying methods – Nut should be sun dried
immediately after harvesting / collection. Drying should be on hard ground,
preferably, concrete / slate drying yards. Quantity of nuts dried per square
meter area shall not exceed 20kg. Uniform drying can be achieved by constantly
turning nuts over to prevent partial / non-uniform heating / drying. Freshly
harvested nuts normally require three days of sun drying.
3.
Proper storing methods – Dried nuts should be stored
in jute / sisal bags [80kg of raw nuts per bag] and not heaped or stored in
silos to avoid warm humid condition in storage room. Storing raw nuts in woven
HDPE bags is not recommended. While storing, it is necessary to provide proper
wooden Dunn age to prevent damage to the cashew nuts in bags by avoiding direct
contact of bags to the Warehouse floor. This can be economically achieved by
keeping bamboos, criss-crossed, tied and placed on the warehouse floor.
Dried
nuts should be stored in well-ventilated, fly-proof place at low humidity. The
storage space should be free of stored product pests and well insulated to
prevent water seepage during rains.
Cashew
processing - process flow
1. Steam
Cooking
2.
Shelling
3. Borma
Treatment
4.
Humidification
5.
Peeling
6.
Grading
7.
Conditioning
8.
Filling & Packing
Steam
Cooking
The raw
cashew nuts, sun dried and stored in the warehouses, are steamed in boiler
[without steam pressurizing the cooker vessel] for about 30 minutes. The
cooking time is varied depending upon the conditions of cashew nut and
atmospheric conditions. The steaming expands the shell and softens the nuts due
to penetration of steam into the shell. After steaming, the nuts are air-cured
by spreading out on the floor in the shade. These ultimately harden the shell
and make it fit enough for de-shelling in the manually operated cutting
machine.
The steam
processing preserves the original color of the cashew kernel inside the nut.
The cut shells of steam roasting process yield quality Cashew Nut Shell Liquid
[CNSL].
Shelling
The Steam
cooked and air-cured Cashew nuts are de-shelled by hand and leg operated
cutters. Two workers work on one cutter, one de-shells the nut and the other
worker retrieves the kernels from the cut opened shell.
The nuts
are fed one by one manually between the two sets of blades to fit the contour
of the fixed blade. The pressing of the pedal pierces the cashew nut on the
convex side by means of two blades. The two blades are used to split the nuts
by operating the handle of the cutter. After de-shelling, the nut falls freely
due to gravity and is collected beneath the cutter. The operator’s assistant
works upon each de-shelled nut and takes out the cashew kernel embedded inside
the shell.
A pair of
skilled worker normally de-shells about 80kg of raw cashew nuts in 8 hrs, which
yields approximately 20 kg of cashew kernels. De-shelling in the mechanical
cutter soils the hands of operator, causing corrosion due to CNSL oozing out
from the shells due to impact of blades. It is a general practice to rinse the
hands with suitable oil, mostly castor oil, to protect the hands from corrosive
shell oil. Alternatively, suitable water soluble and washable protective
chemical coating like “Kerodex” cream can be applied to the hands for the
purpose. In some places workers use wood ash or white cement for the purpose.
Heat
treatment of unpeeled kernels [Borma treatment]
The kernels,
after they are removed from the shells have to be dried in order to loosen the
red skin adhering to the kernel for easy peeling. A few processors adopt
conventional tray drier commonly known as “Borma”. The outer sides of borma
chamber are heated by means of flue gas generated by burning oil-extracted
shell-cake at the bottom. The inner chamber heats up by radiation of heat.
The above
system is becoming obsolete due to poor heat transfer efficiency. In the
absence of air-circulation inside the chamber, heating is non-uniform. This
results in over heating of kernels causing scorching of kernels in spite
changing of trays and turning the kernels in the trays periodically.
The
conventional “Borma” is presently being replaced by more efficient electrical/diesel
operated tray driers. This system ensures uniform heating of kernels for a
pre-set temperature [80° C] and time [2 ½ to 5
hours] by means of reliable electronic controller and timer. This system
reduces the heating time considerably and does not requires periodic changing
of trays during heating, as uniform heat is maintained through out the drier by
forced air circulation. This system preserves the original color of the Cashew
Kernel and quality consistency is achieved within a batch and in every batch
treated.
Humidification
of unpeeled cashew kernels
The Borma
treated cashew kernels are humidified [Moisturized by water-mist] by means of
electrical humidifiers. The cashew kernels in trays are kept in trolleys and
are humidified in a closed room for a particular period depending on the
atmospheric conditions and moisture level of cashew kernels. The treatment time
varies anywhere between 15 - 20 minutes, depending on the condition of the
Cashew kernels under treatment and climatic conditions.
The brown
skin [Testa] of the humidified kernels undergoes shrinkage due to sudden
cooling. This helps to dislodge the hold [Adhesion] of skin to the kernel.
Peeling
of conditioned cashew kernels
The
cashew kernels conditioned as above are now ready for peeling. Peeling of the
Testa is done manually; usage of sharp edges of knife is discouraged as it
causes scraping of kernels. Scrapping mars [spoils] the look of the cashew
kernel and is more pronounced after oil roasting. However knives are very
selectively used on a very small quantity of cashew kernel, whose skin does not
peel off easily in manual peeling. Major classification / grading of kernels
into wholes, brokens and rejections are done at this stage. A skilled laborer
can peel approximately 6 to 8 kg in a day.
Grading
of cashew kernels
The
peeled kernels are manually graded in natural light by skilled labour. The
cashew kernels are graded on the basis of shape, size and color. International
specification and standard for grading are widely followed in the industry.
The color
grade chart officially issued by the Cashew Export Promotion Council of India
serves as a guide for color grading. Normally a skilled laborer can grade
anywhere between 20 to 25kg of cashew kernels per day depending upon the
grader’s skill and the size of the kernel being graded. For grading brokens
into LWP, SWP and BB graded mechanized wire-mesh sieves are used.
Conditioning
of graded cashew kernels
The
moisture percentage permitted in the graded cashew kernel is 5% max by weight
at the port of importation. While a moisture level above 4% at the time of
final packing is not preferred as the same may cause fungal growth and aid
infestation, low moisture level below 2% is undesirable as it causes breakage
of kernel during further processing for value addition and shipment.
Processors,
by and large control the final moisture level up to 3%. Cashew kernels are
humidified to increase moisture percentage to the required level or heat
treated to reduce the excess moisture before final packing.
Filling
and packing
The
grated and moisture conditioned cashew kernels are filled in 18 l/ square tins,
25lbs (11.34kg) to a tin. The cashew kernels are fed into the vibratory filling
machine through a pneumatic Foreign Matter Segregator (PFMS). 8 Tins (Leak
tested and Tar weighed) are filled at a time; filled tins are then weighed for
a net weight of 11.34 kg plus or minus 10gm using electronic weighing scale.
The weighed
tins are “Vita Packed”. Vita packing is the process of vacuumizing and
injecting inert gas viz. Carbon-di-oxide or Nitrogen into the cashew kernel
filled tins. The gas infused tins are hand-soldered hermetically using lead
free solder.
Two tins
are packed in a unit carton and strapped and stencil marked for shipment. The
consignment is shipped after per-shipment inspection formalities.
Modern
Packaging system - Cashew Kernels can also be
packed in multi-layer flexible pouches; gas flushed and sealed – 25 pounds net
per pouch. All importers in USA and Europeprefer this system of
packing.
