Storage of grain
By Dr Ali Muhammed Khushk and Bhugro Mal
THE storage of grain
requires proper care and planning. It releases and
absorbs heat and moisture from the surrounding. Insects
infesting stored foods can be divided into primary and
secondary grain feeders. Insects capable of infesting
undamaged grains include moths, weevils, lesser grain
borer and grain beetle.
and moisture are most important factors as these not
only affect the quality, but also give rise to insect
pests and fungi. The optimum temperature for most insect
pests is around 28-32°c. They are able to develop and
multiply between 15.5 to 18.3°c. Many can live long at
low temperatures but their activity is reduced very
much. These feed on dry materials need certain amount of
The moisture requirement varies from species to species
but practically all of them need more than 10 per cent
moisture with 14 per cent optimum. Therefore, grain with
less than 10 per cent moisture is safe for storage.
Micro-organisms also develop at high moisture content.
If wheat is stored at a moisture content of 14 to 18 per
cent at 21.1°c, it will be attacked by Aspergillus
restriculus. Grain in storage also undergoes chemical
changes with a change in moisture. Increased respiration
of stored grain under high temperature increases fatty
acids and reduces sugar content.
At high moisture level, carbohydrate fermentation may
occur with the production of alcohol or acetic acid
resulting in a characteristic sour odour. Storage of
grain above 16 per cent moisture may reduce seed
viability to a great extent. High moisture content not
only deteriorates quality, but also occupies more space
as its bulk increases.
At the time of harvest, the grain should be dried until
the moisture content is less than nine per cent. The
storage of grain requires complete knowledge of all
In Pakistan, public sector agencies are involved in the
procurement, handling, marketing, storage and supplies
include the four provincial food departments and
national public grain agency, the Pakistan Agricultural
Services and Supplies Corporation (Passco).
The rated storage capacity with these agencies is 4.34
million tons out of which 2.45 million tons is with the
Punjab Food department; 0.71 million tons with the Sindh
Food Department; 0.16 million tons with the NWFP; 0.44
million tons with the Balochistan Food Department; 0.45
million tons with Passco; and about 0.13 million tons
with other agencies.
Sindh and Punjab have surplus quantity which they supply
to deficit provinces. Passco mostly operates in Punjab
in areas not allocated to food department.
Storage structures at public level: The government has
constructed large sheds commonly called house type
godowns constructed with some variations to suit
climatic and other conditions of the area.
In Karachi each unit measures 51.21m x 12.19m with a
storage capacity for about 1,500 tons of wheat. Door and
ventilation arrangements are made to provide aeration to
stored grains. These types do not provide protection
from insect infestation and are impossible to make
gas-tight for fumigation.
Due to poor maintenance, the structures have
deteriorated with the passage of time and considerable
grain loss takes place in these godowns due to insect
Binishells: These are dome-shaped structures. The height
of the dome in the centre is about 10m with floor having
diameter of about 32m. One binishell has the capacity of
about 1,500 tons of grain. The structure gets heated up
in summer, particularly in Sindh and Punjab resulting in
rapid multiplication of insect pests. The structure is
also difficult to make gas tight for fumigation.
Silos: There are two types of silos, concrete and metal.
Each accommodates about 5,000 tons of grain. Most are
not fully utilized due to operational difficulties.
Storage at village level: Major proportion of food
grains is held in the houses, in villages and towns, in
small but numerous types of receptacles for self
consumption. The receptacles may be gunny bags, earthen
and metallic bins and pots of various sizes, pallies,
kharas, bakharies etc.
During handling and storage considerable quantity of
food grain is lost between harvest and consumption. If
safe measures are adopted, both quantitative and
qualitative losses can be avoided at all levels.
Cleanliness is a primary prerequisite for preventing
insect damage in stored products. Most of the insects
and mites live in empty godowns or granaries as well as
in stored food. Therefore, it is important to destroy
them before the granaries are re-filled with grain.
Prior to storage, all bins, granaries and surrounding
area should be thoroughly cleaned to get rid of insects
and mites living in cracks and crevices. Floor, ceiling,
walls and doors should be thoroughly swept, cleaned and
the collected rubbish should be burned or removed far
away from the storage area.
Empty godowns should also be spread with deltamethrin to
kill the already available insects. All cracks, crevices
and holes should be filled with cement plaster and made
birds and rodent proof. Adequate ventilation is
Storage godowns should be waterproof and gas-tight to
protect grain from moisture and leakages during
fumigation. Walls should be whitewashed with white or
light coloured emulsion paint. Grains having moisture
less than 10 per cent should be stored. Bags should
never be stored near the walls of godowns. Insect free
transport should be used for shifting grain from one
area to another. Already infested grains should never be
As soon as the grain is brought into godowns, the
already available insects begin their job of infesting.
Therefore, fumigation just after storage is necessary.
In case of house type godowns, spray with deltamethrin
at recommended dose on all exposed surfaces of godown,
fabric and periphery of stacks. Thereafter, fumigate
twice with Aluminum phosphide (ALP) tablets at the rate
of three tablets per cubic meter, in two equal doses
i.e., 1.5 tablets on the first and fourth day,
Banishells due to their high leakage rate are difficult
to be fumigated. In these godowns, spray with delta
methrin as before and thereafter fumigate with phophine
tablets using the multiple dose i.e., first dose at the
rate of 1.5 tablets per cubic meter, followed by
application of one tablet per cubic meter each on 3rd,
5th and 7th, day.
But after fumigation and spray godowns should be
regularly inspected for insects, rodents, molds and
heating spots. As insects mostly move at dusk, it is
therefore, better to inspect for live insect pests in
dim light in the evening with torch, but the damage
should be worked out in daylight. Detailed examination
of dust, cracks and crevices for sign of insects should
Do not allow spoilage of grain in the godown. Always
keep the godown tidy and occasionally give the walls,
floor, ledges beam and doors a good brush out, discard
rubbish and treat the infested goods promptly. Perform
periodic check of roof, gutters, walls, floor and doors.
Ventilators and doors should be opened during dry
weather and closed during the period of excessive
humidity. In case if moisture content of grain exceeds
11 per cent, it should be dried at once, because high
moisture is conducive for the attack of insects and
formation of mold. Wet grains can be dried by spreading
in one inch layer on cemented floor on hot sunny days
and given 2-3 turnings during a day.
Courtesy: The DAWN