FOOD GRAIN STORAGE

Costs and incentives to store

Both producers and consumers benefit from stable prices, which reduce the uncertainties associated with planning farm
investment and household expenditure. However storage involves costs, and the only way in which these costs can be recuperated
is through a price spread. If storage is to be profitable, people who store grain must receive a price on sale which at least covers
the costs of storing the grain since harvest. These include:

 The cost of the store itself (often a rental cost);

 Labour and supervision;
 Pest control;
 Storage and spillage losses; and
 Cost of capital invested in the grain.

In practice, the costs of storage depend on the commodity stored, on the type of storage system, and on unpredictable and
variable factors such as pest incidence and climatic conditions. Storage costs also depend on the circumstances of the
person, the business or the institution who is storing. The most variable component of storage costs is the cost of capital. For
a small farmer or trader, capital may be scarce and costly, and their only access to loans may be from money lenders
charging rates of 10% or more per month. On the other hand a Government Marketing Board may have preferential access
to loans at low interest, at rates of as low as 10% per annum. There is, therefore, no single cost of storage.

Biodeterioration

The condition of stored grain is determined (Lacey, 1988) by a complex interaction between the grain, the macro- and micro-
environment and a variety of organisms (including microorganisms, insects, mites, rodents and birds) which may attack it.

Grain provides an abundant source of nutrients, and the natural consequence of the type of stable ecosystem described above will
normally be spoilage (biodeterioration) of the grain, caused by the organisms.

The extent of contamination by moulds is largely determined by the temperature of the grain and the availability of water and
oxygen

The interaction between grain temperature and moisture content also affects the extent of mould colonisation.

Insects and mites (arthropods) can, of course, make a significant contribution towards the biodeterioration of grain,
through the physical damage and nutrient losses caused by their activity.

In general, grain is not infested by insects below a temperature of 17°C whereas mite infestations can occur between 3 and
30°C and above 12 per cent moisture content.

Mould growth is also regulated by the proportions of oxygen, nitrogen and carbon dioxide in the intergranular
atmosphere.

The significance of mycotoxins

Mycotoxins have been implicated in a range of human and/or animal diseases and occur in a variety of grains. The
ingestion of mycotoxins can produce both acute (short-term) and chronic (medium/long-term) toxicities ranging from
death to chronic interferences with the function of the central nervous, cardiovascular and pulmonary systems, and of the
alimentary tract.

The mycotoxins described in this chapter, as symptoms of biodeterioration, are acutely toxic, carcinogenic,
immunosuppressive and oestrogenic; and have been the cause of serious human and/or animal diseases. The potential
 immunosuppressive role of mycotoxins in the aetiology of human disease is an especially important issue which requires
further careful study. Every effort must be made to minimise the occurrence of mycotoxins in food and feed grains .

Quality characteristics of grains

The more important quality criteria as they relate to grading of grain are described in the following sections.

Intrinsic Qualities

(i) Colour

Cereal grains are pigmented and range through the colour spectrum from very light tan or almost white, to black. Where
extractive milling is required, highly-pigmented varieties may give low yields of white flour.

(ii) Composition

Composition, e.g. protein, carbohydrate, lipids and their breakdown products, qualitatively influences product acceptability, by
affecting texture and taste. Quality changes evolve slowly in stored grain and more rapidly in milled or processed intermediary
products.

Some grain components, for example husk, are inedible and quantitatively influence product yield and gross nutrient available to
the consumer.

(iii) Bulk Density

Each type or variety of grain when in optimum health, fully mature, etc. has a characteristic bulk density. This is defined as the
weight per standard volume measured in a standard manner. The same characteristic is variously known as 'test weight', 'bushel
weight' or 'specific weight

iv) Odour, aroma

Most grain types, when fresh, have a distinctive natural odour or aroma. This is generally accepted as an indicator of good
quality, although some people prefer grain which smells 'old' or even fermented.

Size, shape

Rice, as a whole-grain food, is classified by size (length) and shape (length:breadth ratio). Other grains also have size considered
in their specification. In general a small range in size assists with processing and handling.

Induced Qualities

(i) Age

During the post-harvest phase, grain undergoes complex biochemical changes termed 'aging'. Changes to carbohydrate, lipids and
protein fractions result in, for example, firming of texture in rice on cooking, and increased gas-retention capability in wheat
flour. For most consumers, the effects of these changes are considered to be desirable. When plotting consumer acceptability of a
grain product against its age since harvesting, generally it is considered to be maturing during the upward curve of the graph, and
deteriorates only when the curve changes direction downwards.

(ii) Broken grain

Grain is marketed normally in whole grain form and is considered to be of inferior quality if broken. Breakage may occur from
fissures as a result of excessive drying/weathering conditions in the field or during handling. Breakage reduces quality by
reducing acceptability and by increasing susceptibility to infestation during storage. This affects milling yield by contributing to
weight loss.

(iii) Chalky or immature grain

Empty grains result from sterility and pre-harvest infections and insect attack. Immature grain content is affected by time of
harvest. In rice, immature grains are greenish in colour. Thin white (usually opaque) grains are caused by incomplete grain filling
and may result from pests or disease. Chalkiness is caused by incompletely filled starchy endosperm which disrupts light
transmission, causing opaque regions. In most cereals, chalky areas have lower mechanical strength on crush tests and may break
during handling. The broken portion is more easily invaded by certain storage pests.

(iv) Foreign matter

Dilution of the prime product by foreign matter reduces the value, and also may affect handling and processing. Foreign matter
may be subclassified as:

animal origin - insects and their products, rodent excrete, etc;

vegetable origin - straw, weeds, seeds, dust, micro-organisms/toxins;
mineral origin - stones, mud, dust, glass, metals, oil products, pesticide residues.

Elements from all three subclasses may render the grain unfit for consumption. Potentially the greatest threat to health probably is
from micro-contamination with the bacterial products of poor sanitation, and with toxins and chemical pesticide residues.

(v) Infested, infected grain

Grain mass, and therefore yield, is reduced by infestation. Contamination not only has direct food hygiene implications but also
indirect ones, as invading micro-organisms may produce toxins under certain conditions which may lead to acute or chronic
illness.

(vi) Mixed varieties

A mixture is an indication of poor pre- and post-harvest management and supervision, e.g. seed selection, lot segregation and
treatment, contamination, etc. Grains differing in size and other characteristics affect processing potential. Whilst preference for a
particular variety may be influential nationally or regionally, internationally-traded grain is recognised usually by grain type
rather than by variety e.g. yellow or white maize. Exceptions do occur, e.g. basmati rice, (see odour, aroma).

(vii) Moisture content

Moisture content (me) of grain plays a crucial role in post-harvest processing and is associated with most of the induced
characteristics. Water vapour will diffuse throughout a bulk of grain and the mc will tend to equalise. 'Hot spots' may occur at a
site of increased respiration (caused by sprouting, infestation or microbial activity), and condensation may occur on cold grain or
containers.

Equipment for obtaining primary samples from bagged grain

(i) Simple bag sampling spears

(ii) Double-tube sampling spears

(iii) The Produce-Flow sampler

Equipment for obtaining primary samples from bulk grain

 (i) Equipment for sampling static bulk grain

Double-tube sampling spears (

Manually-operated deep bin probes

Pneumatic grain samplers

Auger-type sampler

(ii) Equipment for sampling moving grain.

The Pelican sampler

The Ellis Cup sampler

Limpet-type sampler

The diverter-type sampler

Quality determination, equipment and methods

grain quality may vary with the variety or type of grain selected by the farmer. It will be influenced by climatic and soil
conditions during the growing season, cultivation practices, weather conditions at harvest, and by harvesting techniques. Apart
from short-term aging or maturation immediately after harvest, quality cannot be improved during storage, handling and
processing - on the contrary, it is easily lost.

Assessment of grain quality

Many assessments are commodity-, product- or end user-specific. Of the wide range of properties, bulk density and foreign
matter are commonly assessed for most types of grain. In addition, the influence of moisture content on other grain qualities,
as well as the simple economic fact, make it important for quantification.

(i) Bulk Density

(ii) Foreign Matter

Most grain quality standards state that the screens in sieves used for the assessment of foreign matter content should consist
of perforated metal plate conforming to specifications laid down by national or international standards organisations

(ii) Moisture Content

Grain harvesting, threshing and cleaning

Rice Harvesting and Threshing

(i) Harvesting methods

Manual harvesting
Mechanized harvesting

During past decades the mechanization of rice harvesting has rapidly evolved. It first developed in Japan, then in Europe and has
now reached many tropical countries.

(iii) Threshing methods

After being harvested paddy bunches may be stacked on the plot. This in-field storage method results in a pre-drying of the
rice ears before threshing, the purpose of which is to separate seeds from panicles.

Traditional threshing: the traditional threshing of rice is generally made by hand: bunches of panicles are beaten against a
hard element (eg, a wooden bar, bamboo table or stone) or with a flail.

Mechanized threshing

(iii) Combined harvesting and threshing methods

Combine-harvesters, as the name implies, combine the actions of reaping and threshing

(iv) Strippers

Because of their size, conventional harvesters and combine harvesters prove unsuitable for many rice growing areas with small
family farm holdings. In response to this problem, research services, during the last ten years, have developed small-sized
machines for harvesting the panicles without cutting the straw. Such machines are known as strippers.

Grain Cleaning

Threshing operations leave all kinds of trash mixed with the grain; they comprise both vegetable (e.g. foreign seeds or kernels,
chaff, stalk, empty grains, etc.) and mineral materials (e.g. earth, stones, sand, metal particles, etc.), and can adversely affect
subsequent storage and processing conditions. The cleaning operation aims at removing as much trash as possible from the
threshed grain.

The simplest traditional cleaning method is winnowing, which uses the wind to remove light elements from the grain

(i) Mechanized cleaning

The most rustic equipment is the winnower

Natural and solar drying

Sun Drying

The traditional practice of grain drying is to spread crop on the ground, thus exposing it to the effects of sun, wind and rain

Crib Drying

Compared with paddy, cob maize can remain at relatively high moisture contents, in excess of 20% with natural ventilation for
considerably longer periods, from one to three months.

1.Solar Dryers
An improved technology in utilizing solar energy for drying grain is the use of solar dryers where the air is heated in a solar
collector and then passed through beds of grain. There are two basic types of solar dryer appropriate for use with grain: natural
convection dryers where the air flow is induced by thermal gradients; and forced convection dryers wherein air is forced through
a solar collector and the grain bed by a fan.

2.Mechanical dryers

Storage at farm/village level and in warehouses

Temporary Storage Methods

Such methods are quite often associated with the drying of the crop, and are primarily intended to serve this purpose. They
assume the function of storage only if the grain is kept in place beyond the drying period.

(i) Aerial Storage

(ii) Storage on the ground, or on drying floors

This method can only be provisional since the grain is exposed to all pests, including domestic animals, and the weather.
Usually it is resorted to only if the producer is compelled to attend to some other task, or lacks means for transporting the
grain to the homestead.

(iii) Open Timber Platforms

A platform consists essentially of a number of relatively straight poles laid horizontally on a series of upright posts. If the
platform is constructed inside a building, it may be raised just 35-40 cm above ground level to facilitate cleaning and
inspection. Platforms in the open may be raised at least 1 metre above ground level. They are usually rectangular in shape,
but circular or polygonal platforms are common in some countries .

Long-term Storage Methods

(i) Storage baskets (cribs) made exclusively of plant materials

In humid countries, where grain cannot be dried adequately prior to storage and needs to be kept well ventilated during the
storage period, traditional granaries (cribs) are usually constructed entirely out of locally available plant materials: timber, reeds,
bamboo, etc. (Figure 6.4.). Under prevailing climatic conditions most plant material rot fairly quickly, and most cribs have to be
replaced every two or three years - although bamboo structures may last up to 15 years, with careful maintenance.

(ii) Calabashes, gourds, earthenware pots

These small capacity containers are most commonly used for storing seed and pulse grains, such as cowpeas. Having a small
opening, they can be made hermetic, by sealing the walls inside and out with liquid clay and closing the mouth with stiff clay,
cow dung, or a wooden (cork?) bung reinforced with cloth.

If the grain is dry (less than 12% moisture content) there there is usually no problem with this kind of storage.

(iii) Jars

These are large clay receptacles whose shape and capacity vary from place to place. The upper part is narrow and is closed with a
flat stone or a clay lid: which is sealed in position with clay or other suitable material. Generally kept in dwellings, they serve
equally for storing seeds and legumes. So that they may remain in good servicable condition, they should not be exposed to the
sun and should not be either porous or cracked.

(iv) Solid wall bins

Such grain stores are usually associated with dry climatic conditions, under which it is possible to reduce the moisture content of
the harvested grain to a satisfactory level simply by sun-drying it. Solid wall bins are therefore traditional in the Sahel region of
Africa, and in southern African countries bordering on the Kalahari desert.

(v) Underground Storage

Practised in India, Turkey, sahelian countries and southern Africa, this method of storage is used in dry regions where the water
table does not endanger the contents.

The advantages of this method of storage are:

 few problems with rodents and insects;

 low cost of construction compared to that of above-ground storage of similar capacity;
 ambient temperatures are relatively low and constant;
 hardly visible, and therefore relatively safe from thieves;
 no need for continuous inspection.

The disadvantages are:

 construction and digging are laborious;

 storage conditions adversely affect viability; the stored grains can only be used for consumption;
 the grain can acquire a fermented smell after long storage;
 removal of the grain is laborious and can be dangerous because of the accumulation of carbon dioxide in the pit, if it is
not completely full;
 inspection of the grain is difficult;
 risks of penetration by water are not small, and the grain at the top and in contact with the walls is often mouldy, even
if the rest of the stock is healthy.

Temporary Storage Methods

It is recognized that, although temporary storage methods are the least desirable, there are circumstances in which they are
unavoidable. The following suggestions and recommendations for improving such storage methods are offered, on the
understanding that more permanent solutions to problems should be sought wherever possible.

Little can be done to improve aerial storage except, perhaps, to suggest that the bundles of cereals may be safer if suspended in a
well ventilated part of the house; or above a fireplace where insects may be deterred and the moisture content of the grain may be
reduced.

As far as storage on the ground, or on floors is concerned, the grain is less exposed to risk if it is placed on wattle mats or the
like laid on the ground or floor. Drying floors could be improved by making them of concrete; or by stabilising the earth
chemically or with natural material such as néré juice. Larger animals are less likely to spoil the grain if such floors are
constructed near the house, where they can be better guarded.

Open timber platforms may be improved by fitted rodent barriers around the supporting posts.
Long-term Storage Methods

The upright poles which support the platforms of traditional storage baskets (cribs) should be at least 80 cm high, and protected
against termites as described above.

lternative storage technology at farm/village level

Sacks

Wherever grain is grown on a commercial basis, buying agencies often issue empty sacks to producers so that they may be filled
on the farm. The buying agency may then collect the bagged grain from the farm, or the producer has to deliver it to the nearest
collection point. In either case, the producer has to store the sacks of grain for some time before they are sold. During this period
precautions have to be taken to ensure the safety of the grain and maintain its quality .

Metal or Plastic Drums

Drums are often used as storage containers in the house and serve notably for the storage of cereal seeds and pulses.

Plastic drums are used intact or after having the upper part cut off to facilitate loading and unloading. Otherwise, plastic lends
itself poorly to adaptation because it is relatively weak: at most, a lockable outlet can be added. If the lid is tight fitting and the
drum is completely filled with grain, any insects present will deplete the oxygen in the drum and die.

Alternative Solid Wall Bins

In some countries grain storage workers, rather than modifying traditional storage structures, have developed significantly
different storage bins. A few examples of these are described below.

(i) The "Pusa" bin.

Developed by the Indian Agricultural Research Institute (I.A.R.I.), these silos are made of earth or sun-dried bricks; they are
rectangular in shape and have a capacity of 1 to 3 tonnes.

(ii) The "Burkino" silo

(iii) The "USAID" silo
(iv) Concrete/cement silos
(v) Metal Silos
(vi) Synthetic Silos

The Purposes of Warehouses, and Basic Requirements

Warehouses are intended for the storage and physical protection of goods. In the context of grain storage, 'goods' primarily
refers to bagged grain. It may also include materials and equipment required for the packaging and handling of bagged
grain, and storage pest control; although, in an ideal situation, such items should be stored separately. The distinction is
made between warehouses and flat stores, which are designed rather differently for the storage of grain in bulk and are
discussed in Chapter 7.

Locating a Warehouse
 The approximate location of a proposed warehouse for grain storage will have been decided already. However, the
determination of its exact siting is a matter for engineers. If a large warehouse is planned, it is always prudent to involve
local Civil Engineers at this stage.

Several factors need to be considered in selecting a suitable site. In the first instance the topography of the area has to be
studied. It is preferable to erect the warehouse on level ground, ideally slightly raised above the surrounding area, which is
well drained and not prone to flooding. Low locations must be avoided. If it is difficult to find a level area then the least
undulating or sloping area should be selected, and the site should be oriented along contour lines, in order to minimise the
amount of levelling and filling in to be done.

e warehouse should also be easy to clean and maintain (there is no point in using components which are not readily replaceable or
repairable); and it should provide good working conditions.

(i) Foundations and Floor

Unstable clay soils and areas which have been filled in should be avoided wherever possible, because they involve the risk of
subsidence. In all cases, it is necessary to dig down to a point where the soil-bearing pressure is 150 kN/m2 or better.

(ii) Walls

Most modern warehouses are constructed with a framework, usually of reinforced concrete.

(iii) Roof

Internal pillars supporting roof frames should be avoided because, as previously stated, they can interfere with pest control and
other stock management procedures. Instead, roof frames should be designed so that they transfer the weight of the roof to the
supporting columns (in framed buildings), or to the walls if the warehouse is small.

(iv) Ventilation

Ventilation openings are necessary for allowing the renewal of air and reducing the temperature in the warehouse, they also allow
some light to enter it. If such openings are

located too low down they can be the source of numerous problems: entry of water, rodents, thieves, etc. These problems are
avoided when ventilators are placed under the eaves. They should be fitted on the outside with anti-bird grills (20 mm mesh) and
on the inside (10 cm behind the grills) with 1 mm mesh screens (removable for cleaning) which will deter most insects.

(v) Doors

The number of doors will vary according to the size of the warehouse. If possible there should be at least two doors, so as to be
able to rotate stocks on a 'first in, first out' basis. Hoever, this may not be possible or practical in a very small warehouse.

(vi) Illumination

Adequate light in a warehouse is an important factor as far as the safety of workers inside it is concerned. However, there can be
problems in providing sufficient natural light while satisfying other technical aspects at the same time.

Bulk storage

Factors influencing the choice of bulk store

Compared to most other foodstuffs, such as meats and vegetables, grains are relatively easy to store. If grain is kept insect-free
and below its safe moisture content, it will keep for many years with minimal loss of quality or nutritional value. Low
temperature is an important factor in minimising insect activity and in maintenance of nutritional quality in general. Storage at
or below the safe moisture content is essential for prevention of deterioration caused by microorganisms and insects.
Where insects are present, temperatures are high, and most especially where moisture content is above safe levels, then
storage of grain becomes both risky and difficult, and losses will be difficult to avoid. It is in these circumstances that the type of
store and its design become critical to the safety of the stored grain. It is worth remembering that most often, the value of the
grain (in dollars-per-tonne) is usually greater than the cost of the structure in which it is stored. Minor expenditure in improving
the quality of the store can thus be quickly recovered if commodity losses are commensurably reduced.

Selection of Storage Type

Once a storage need is identified, the choice arises as to the type of store that is most suitable for a particular application. The
following storage options may need to be considered: round or rectangular, tall or short, steel or concrete, flat floored or
hoppered, permanent or temporary.

Some basic guide-lines, or principles, are offered:

(i) Round or Rectangular

In terms of structural cost per tonne of storage, round stores are generally more economical than rectangular ones.

(ii) Tall or Short

In the case of flat bottom stores, structural efficiency is also increased by minimising the height of the structure. For a given
volume of storage, the lower the height of the walls, the more grain pressure is applied directly to the floor surface and the less
load there is on the walls. Furthermore, the minimum structural surface area (and hence cost) for a given volume of grain, is
achieved if the wall height is relatively low. For instance in the case of a cylindrical 'tank' with a conical roof, the minimum
surface area of walls and roof is achieved when the wall height is around half the radius of the bin. It is thus no coincidence that
the lowest cost stores are generally in the shape of squat cylindrical 'tanks' where the walls are relatively low compared to the
diameter.

(iii) Construction Materials

The choice of construction material is usually between steel and concrete, though in some countries timber or masonry are still
used as alternatives.

The choice between steel and concrete is dependent on a number of considerations, all of which ultimately come down to capital
and operational costs. The fact that in most countries steel and concrete are both so widely used indicates that these costs are
generally not dissimilar.

Sealed stores

When a new grain store is being planned, there should be no question as to whether or not it should be possible to seal it
effectively to make it air-tight for fumigation. The benefits of sealed stores are such that the small costs involved during initial
construction (negligible in many cases) should not warrant consideration. Low-cost sealing is most easily achieved at the design
stage. Retro-sealing of stores which have not been designed to be sealed can be expensive, and in some cases (particularly with
small stores) it can be uneconomical.

Condensation, Moisture Migration and Moisture Diffusion

The question of condensation risk often arises in any discussion about sealed stores, especially in the case of steel structures. Yet
there is little evidence to support the theory that sealed stores actually cause condensation. Theoretically, there should be less risk
of condensation in sealed stores than in unsealed ones provided the grain stored in them is at or below its 'safe' storage moisture
content.
In a properly sealed store at constant temperature, the grain and air mixture are in moisture-equilibrium with each other.
Different grains have different moisture equilibria with air, and for each grain type, the moisture equilibrium level changes
slightly with temperature.

Methods of Sealing

The easiest stores to seal are fully-welded steel silos, since the structure is effectively sealed by virtue of its welded construction.
Concrete silos can also be sealed with ease provided joints are properly detailed, and care is taken to prevent cracking of the walls
(as discussed above). In either case (with both steel and concrete silos), attention is needed to the design of openings in the
structures: grain inlets and discharge valves, man access doors, etc

Aeration

Ambient Aeration

Aeration is a process of forcing air through grain to reduce its temperature. It is a very useful storage management tool which can
preserve grain from deterioration, especially where the moisture content of the grain is above its safe level. Aeration can be used
as effectively in sealed stores as in unsealed ones - sealed stores merely requiring the provision of an air-exhaust ventilator which
can be sealed whenever fumigation is to be carried out.

Refrigerated Aeration

Aeration with refrigerated air achieves much lower temperatures when ambient conditions are warm. It is an expensive method of
disinfestation compared to fumigation, but can be justified for storage of grains such as malting barley and seed grains in hot
conditions, where maintenance of germination viability is important.

By recirculating the cooling air, it is possible to maintain a sealed storage system. In this way the grain may first be fumigated to
render it insect-free, and then cooled to preserve quality, with the fumigant still present.

Costs of bulk storage

a rough rule of thumb, the costs of modern bulk grain storage and handling facilities can be broken down roughly as follows:

Storage Component: 40 to 60%

Structures and Supports 10 to 20%
Mechanical Equipment 20 to 40%
Electrical and Controls 10 to 20%

Obviously, there are many instances where storage costs are much less than 40% - for instance in high throughput facilities where
the 'storage' component is no more than a shortterm buffer to allow optimisation of the use of the handling equipment.

But in true 'storage' situations, where the purpose of the facility is to hold grain for an extended period of time, it is generally the
case that the storage structures account for the largest component of the total cost. Thus it is normal practice to develop a design
for a grain handling facility around the storage component; in other words to estimate the storage volume required, evaluate the
type of store best suited to the requirements, and then to design the conveying and other systems to suit.

Insect control
Integrated pest management (IPM) in the control of storage insects

Pest control measures, in general, have to be integrated into an operational system, be it large or small in scale, if they are to
be effectively applied. This is a basic principle, not a novel concept, but it connects well with the modern idea of Integrated Pest
Management (IPM). ntegrated pest control can be defined as the acceptable use of practicable measures to minimise, cost-
effectively. the losses caused by pests in a particular management system. For the measures to be cost-effective they must be
appropriate to and acceptable into that system. They may be simple or complex but they must suit the system objectives and
its technical capabilities. Furthermore, in this context, cost-effectiveness requires that all costs and benefits, including
sociological and environmental effects, should have been taken into account.

Chemical control techniques

The chemical compounds, including both fumigants and contact insecticides, for use on food grains to
control storage insects.

The use of fumigants

Fumigants are toxic gases used to disinfest a commodity in an enclosure which, ideally, is completely gaslight. The purpose of a
fumigation is thus to obtain a more-or-less immediate disinfestation of the commodity and the space enclosing it.

Developments in fumigant application techniques

(i) Store fumigation

(ii) Sheeted stack fumigation

(ii) Circulatory systems for phosphine

Alternative and supplementary control measures

Physical measures: cleaning and drying and those which may provide alternatives to other forms of control are cooled grain
storage, hermetic storage, thermal disinfestation and, in some circumstances, mechanical disturbance.

aeration and cooling, by natural aeration in small, ventilated stores (e.g. maize cribs), or by forced aeration in larger stores, can
significantly retard the development of insect infestation.

Traditional grain protectants

use of abrasive mineral dusts, natural desiccants like wood ash and various plant materials with repellent or insecticidal
properties .

Modern biological methods

Irradiation techniques and controlled atmosphere storage are included here, although they may also be regarded respectively as
physical and chemical techniques, because their use depends upon radical interference with biological systems or processes.

Controlled atmosphere (CA) storage has become an important addition to the available options for stored-grain pest control.