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Preventive measures in flour mills

Preventive measures in flour mills

Throughout the food chain, the identification, control and extermination of pests in the food industry requires many resources, from producer to manufacturer, carrier to distributor together with surveillance and control by the authorities responsible. Mites, insects and rodents can all be introduced in many ways and forms to the food chain, they can enter through their own efforts into buildings, arrive with raw materials, packaging and machinery or in damaged or returned goods. How we prevent their access and how we control the environment in which food is produced, stored and sold, demands detailed planning and a well organised programme of preventive measures. If a satisfactory result is to be reached, it can only be done by removing or reducing the root causes and conditions favorable to pests. In this way a more permanent solution can be reached without a dependency on chemicals, creating fewer environmental or health problems and less risk of developing resistance and achieving green pest management status. Permanent “designing out” of pests through modification of machinery and buildings can much reduce pest pressure.

Building Design

Grain and grain products in flour mills are at risk of being contaminated by foreign material, insects, microbes and vertebrate pests. There are three types of pests that affect milling process and product quality. Besides structural and exterior pests (such as cockroaches, ants, rodents, birds and exterior flying insects), the type of pests that are most critical to flour mills are stored product arthropods (internal and external feeder insects and mites) found within the commodity (grain and flour). Good engineering for food safety and sanitation are first and most important considerations while setting up a flour mill to avoid these pests. The engineer’s sanitary design decisions have a tremendous impact on operational sanitation and maintenance. Some of the important measures are:

Selecting location and layout: The selection of location is determined by factors, including proximity to nearby industries, sanitary landfills, incinerators, junk yards and service depots that attract rodents and other vermin. The location must be of adequate size to accommodate the immediate building plan and expansion. Crowding limits the options for an efficient and sanitary plant layout creating conditions conducive to pest activity. Designing the building layout should include systems for lighting, environmental & pollution control, cleaning and waste-handling. The final layout should present a smooth, orderly flow of raw materials or ingredients through each manufacturing phase on to the storage of the finished product.

Equipment layout: It is very important to use templates to obtain the best possible layout for good access to all equipment. It should allow adequate space inside, around and under equipment for easier cleaning and maintenance. In general, a clear distance of 36 inches all around equipment is considered the bare minimum. Actually, more space is preferred and should be the rule rather than the exception.

Overhead and ceiling areas: Layout planning applies to overhead or ceiling areas as well as at the floor level. The use of false or suspended ceilings to contain overhead piping and equipment is generally not acceptable. Unfortunately, this area is frequently overlooked and difficult to maintain. Resultantly it often gets heavily infested with insects and a source of recurring infestations. Arrangement of groups of pipes or conduits must also be done with sanitation in mind. Access doors should be provided in the pipe chases for inspection and cleaning. The design should also take into consideration installation of access-platforms and cat walks to permit the overhead cleaning of pipe, conduit, ductwork and equipment.

Floor trenches: When floor trenches are used, they should be watertight, back filled with fine sand, and a concrete knockout slab should be poured over the sand. This would allow for future access should it be necessary. Open trenches or those covered by wood or metal plates inherently create serious sanitation problems and, in general, are not to be considered.

Equipment supports: They should be kept simple and designed to clean. They should not obstruct or the cleaning area surrounding the equipment. For dry manufacturing process like flour milling, ideal construction materials for equipment support is mild steel painted with epoxy base paint. The support should be designed to eliminate ledges and flat surfaces where dust, dirt and product spills may accumulate. Not only is the selection of structural shapes important to sanitation, but so is the arrangement of the shapes. Many ledges, cracks, crevices and dead ends can be eliminated with the proper use of structural members. For example, angle iron or channel used in a vertical manner to form a leg or a hanger creates a difficult to clean crevice at the floor junction. Tubing is better choice for this application.

Lighting systems: Selection of lighting systems and mounting location is important consideration to prevent flying insects invading the structure. Insects are attracted to ultra-violet light emitted by mercury vapour lights and are also attracted to the warmth around light systems. Selecting sodium vapour lighting systems, which are less attractive to insects and installing lights mounted on poles or ground at least 20ft away from building can greatly help in minimizing insect settling on building and gaining access inside.

Controlling manufacturing environment: The mill should be designed to control manufacturing environment where there is need to do so. For example, layout planning must include adequate air exchanges and wet exhaust systems to minimize the otherwise certain sanitation problem of mold. Molds can grow in atmospheres containing less than 15% moisture. Dust collection systems should also be provided where they are needed.

Cleaning systems: Installing Clean-in-place (CIP) systems and Clean-out of place (COP) can help cleaning in much less time, reduce cost and improve cleaning quality, eliminating conditions leading to pest breeding. A good CIP system include wet central cleaning system which pipe a supply of hot water and in some cases cleaning chemicals, throughout the entire facility. The volume and pressure of the water are provided to accommodate the cleaning need. It also includes a central vacuum system for both wet and dry pickup and specially designated areas for cleaning of mobile or portable equipment.

Waste handling systems: The plant layout should also include provisions for handling solid wastes such as product offal, plant refuse and other debris, in addition to liquid wastes. These facilities should be located at the back of the plant and be completely isolated from the milling process. If not handled properly, besides a potential contamination source, waste also attracts vermin.
Pest control systems: A flour mill should consider installing heat sterilization units, a system of sufficient capacity to provide the higher temperatures needed to kill stored product pests. In addition, mechanical equipment can also be added to the milling systems to destroy and remove insect pests. These equipment include infestation destroyer impact machines, aspirators, sifters, and scalpers. In case of large scale operations, installation of instrumentation delivering modified atmospheric treatments should also be considered. Modified atmosphere treatments involve alteration of the proportion of the normal gaseous constituents of air (oxygen, nitrogen, carbon dioxide, and trace gases) to provide an insecticidal atmosphere. The design of storage bins should allow regular monitoring, aeration to reduce issues related to moisture, mold and pest infestation.

Prevention of infestation

When the flour mill building and equipment have met sanitation design needs, the sanitation programme reflects this effort in lower cleaning and pest control costs. The flour mills must meet the challenge of maintaining the structure and equipment in a sanitary condition. The maintenance department personnel are the key to this challenge, their technical skills and knowledge must include good food safety and sanitation practices.

Stored grain and flour are subject to insect infestations and deterioration from molds and bacteria. High grain temperature and moisture, along with dockage and broken kernels and even milled flour, provide conditions that accelerate mold and insect development. Some insects damage grain by developing inside kernels, feeding on the inner endosperm and producing holes in the kernel through which the adult insect exist. These insects are called “internal feeders”. The cycle is repeated when the female lays eggs inside the kernels. Examples of internal feeders are maize weevil, rice weevil, granary weevil, lesser grain borer, and Angoumois moth. The grain (maize, rice, granary) weevils are small recognizable as a group because the head projects forward as a prolonged snout. The adult’s lesser grain borer head projects downward, not forward, and does not bear a snout. The Angoumois grain moth lays its eggs on grain kernels and the larvae bore into the kernels and feed there.

Other insect species that do not develop within the kernels, although they may hide inside cracked grain, making detection very difficult are flat grain beetle, rusty grain beetle, and the foreign grain beetle. They primarily feed on mold. Other species such as the saw-toothed grain beetle, the red and confused flour beetles, the Indian meal moth, and the larger black flour beetle feed on damaged grain or fines.

Packaged and stored grains can be protected from getting infested by having a comprehensive integrated pest management programme that ensures regular monitoring, timely intervention of corrective actions based on (IPM) Hazard Analysis Critical Control Point (HACCP), evaluation and follow ups.
Stored grain: Stored grain management is the organised, long-term approach to maintaining the quality, minimizing chemical control inputs, and preserving the integrity of the grain storage system. Techniques can be integrated into grain storage systems to prevent or minimise losses from insect and mold infestations. These management techniques must focus on the factors that regulate storability, including grain temperature, grain moisture, storage air relative humidity and storage time.

For example:
• Most insect and mold activity is greatly reduced at grain temperatures below 15oC. Planned temperature reductions by controlled aeration can significantly reduce insect population. Mod populations follow similar temperature control patterns. Aeration is the forced movement of air through grain to lower or equalise grain temperatures.
•Higher levels of grain moisture increase the potential for high populations of stored-grain insects and molds. To achieve safe storage moisture contents, force heat or natural air drying of some crops is necessary.

Packaged grain: Although packages can become infested anywhere along the production to marketing chain, they are most likely to become infested during long-term storage. Inside the warehouse, insects attack vulnerable packaging and later jump to sturdier material. To avoid such invasion, packaged products should be rotated sold/distributed or consumed on first-come first-out basis within the shelf-life period.

Packaging should protect the commodity from the point of manufacture to the point of consumption. Stored product insects are one of two types – invaders and penetrators. The invaders, like red flour beetle, confused flour beetle, saw-toothed grain beetle, Indian meal moth, and almond moth look for opportunities to get inside food containers by searching for cracks, crevices and holes. The penetrators like the lesser grain borer, cigarette beetle, warehouse beetle, and rice moth chew holes even into multi-layered packages.


Packages are usually tailored to fit the product and designed to last throughout its shelf life, which is mostly for more than a year. Innovative packaging material can also help minimize insect invasion. Seals and closures can be improved by changing the type or pattern of sealant glue. Closures on bag bottoms are prone to insect entry. Reinforcement as much as top closures can help to eliminate this risk.

Another packaging problem involves smell. Insects are attracted to packages that allow food odors to escape. Certain plastic film overwraps that fit tightly around a package can help prevent insects from smelling its contents. Interior plastic liners like those used in breakfast cereal boxes can be effective, blocking air from carrying aromas outside to hungry insects. An odour neutralizer can also be incorporated into packaging materials. Thus, preventive maintenance becomes the necessary element, paramount for product safety.

Heat Sterilization

The heat sterilization units, a system with sufficient capacity provides the higher temperatures needed to kill stored product pests. In addition, mechanical equipment can also be added to the milling systems to destroy and remove insect pests. These equipment include infestation destroyer impact machines, aspirators, sifters, and scalpers. In case of large scale operations, installation of instrumentation delivering modified atmospheric treatments should also be considered. Modified atmosphere treatments involve alteration of the proportion of the normal gaseous constituents of air (oxygen, nitrogen, carbon dioxide, and trace gases) to provide an insecticidal atmosphere. The design of storage bins should also allow regular monitoring, aeration to reduce issues related to moisture, mold and pest infestation.

Use of insecticides

If a pesticide application is warranted, then ensure that the pest management professional
•  Thoroughly understands the label directions of any pesticide being considered for use (Label is the law)
•  in addition to the label address all the requirement of GMP’s, the individual agency regulations, and the pesticide policies of the organization

A few examples of pesticide use around grains is as follows:

•  Rodent control poison baits (Rodenticides) are not used in the storage areas. A strict count of all bait stations (if installed exterior of the flour mills, grain storage or silos) must be maintained. All bait must be in temper resistant stations. All baits must be cake based to ensure that rodent is unable to carry it back to remote locations. Rodenticide tracking powders shall not be used.
•  Inside the production areas (milling, bagging and storage), pesticide treatments should be confined
largely to injecting crack and crevices or voids where pests are harboring.
•  While treating grain storage areas with contract insecticides (liquid and space – aerosol, fogging, ULV, fumigation) insecticide applications treatments are applied in non-production hours. This allows proper preparation (including cleaning, removing or covering grain, flour, and dismantling equipment) and facilities treating all food production and non-production areas without disturbing employees or contaminating food or equipment.
•  When contact insecticides are used in food areas, all product contact surfaces must be protected, or they must be thoroughly washed before startup.
•  Pesticides if stored on premises should be stored away from food products and food contact surfaces.


There are many chemical compounds which are volatile at ordinary temperatures and sufficiently toxic to fall within the definition of fumigants. In actual practice, however, most gases have been eliminated owing to unfavorable properties, the most important being chemical instability and destructive effects on materials. Prior to “Montreal Protocol”, Methyl Bromide gas was widely used to fumigate stored products including grain and flour. Other fumigant that is also widely used is Phosphine gas (alone or in combination with carbon dioxide).

Veejai Alhuwalia
CEO, Sterling Environment Solution PVT LTD

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