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What are the Different Methods used for Storage of Grains?
Most crops are harvested only once a year. Thus, they are available in plenty during a selective time. For getting seasonal foods regularly throughout the year, they are stored in safe storage.
Cereals or food grains are stored at the following three levels:
1. At the producer (farmer) level (called rural storage).
2. At the trader’s level (this is done by keeping food grains in gunny bags.
3. At the FCI (Food Corporation of India) level (This is done by storing grains in silos).
Storage of Grains – Affecting Factors
During storage, grains and seeds are subjected to spoilage and wastage by various means. This loss has been estimated to be 9.3 percent annually. During storage damage of grains can take place by following two main types of factors:
Biotic factors such as insects, rodents (e.g., striped squirrel, house rat, house mouse, lesser bandicoot, etc.), birds (e.g., parakeet, sparrow, bulbul, blue rock pigeon, crow, etc.), mites and bacteria.
Some Common Insect Pests of Stored Grain
- Gram dhora or pulse beetle (Catlosobruchus maculatus) – Its grub damage stored gram.
- Rice weevil (Sitophilus oryza) – Both grub and beetle (adult) damage rice.
- Khapra or wheat weevil (Trogoderma granarium) – Infests stored wheat.
- Grain and flour moth (Sitotroga cerealella) – Its caterpillars bore into grains of rice, wheat, barley, maize, and jowar.
- Rust red flour beetle (Tribolium castaneum) – Both larvae and adult damage flour and flour products.
- Rice moth (Corcyra cephalonica) – Larvae damage to rice and maize.
- Lesser grain borer (Rhizopertha dominica) – Both grub and adult (beetle) damage the grains, reducing them to perforated shells.
Abiotic factors such as moisture contents and temperature.
(a) Effect of temperature:
The growth of insects and microorganisms in the stored food materials depends upon the fluctuation of temperature. As the maximum growth rate of the insects is at a higher temperature of 30°C to 32°C, the microorganisms and enzymes are most active at 30°C to 40°C. Therefore, the food grains/materials should be stored at a lower temperature, i.e., below 30°C, then the insects and microorganisms, and enzymes will become less active and the damage to the material is minimised.
(b) Effect of moisture:
For safe storage, the moisture content of the food grains should be 14 percent by weight or less. The greater amount of moisture present in food grains increases the rate of decay of food materials caused by microorganisms and enzymes and the population of insects increases rapidly. When these insects respire they release a lot of heat, so the temperature of stored food grain rises.
The rise in temperature of stored food grains due to the heat released by the respiration of a large number of insects, and microorganisms (fungi such as molds, yeast, etc.) is called dry heating of food grains. Another disadvantage of the presence of greater moisture is that it increases the size of the food grains, due to which these grains require more space.
(c) Effect of humidity:
The moisture content present in the air is known as humidity. It promotes the growth of moulds (e.g., Mucor, Penicillium) on the stored food materials. High humidity content also initiates the germination process of stored seeds which also releases heat. Therefore, as the moisture content of the grains increases from 14 to 18 percent, the temperature may shoot up to 66°C. The rise in temperature of stored food grains due to the growth of moulds and fungi and germination of stored food grains under high humidity conditions of air is called wet heating or damp grain heating. Thus, dry heating and wet heating both lowers the quality of stored food grains and badly affect the germination of grains.
A combination of biotic and abiotic factors causes infestation of insects, degradation in quality, loss in weight, poor germinability, discoloration of produce, poor marketability, and economic loss. Therefore, stored grains must be protected from all types of losses and damages.
Preventive and Control Measures
Biotic and abiotic factors which cause the destruction of grains during storage can be prevented and controlled by using the following methods.
The proper time of harvesting a crop is very important because the time of harvesting crop determines the yield of the crop production as well as the storing qualities of the crop products.
At the time of harvesting of the crop, moisture content in grains varies, from 15-35 percent. But, for safe storage, the seeds and grains should have a moisture content below 14%. So the step of drying grains is a vital preventive measure.
The harvested food grains should be dried by spreading them over plastic sheets or on the cemented floor (This is done because if the grains are spread directly on the ground, they will absorb more moisture from the ground). All the sun-dried food grains are allowed to cool to room temperature before storing them. On commercial bases, a mechanical drier with hot air is used.
The grains and other agricultural produce should be properly cleaned before their storage. They should be filled in new gunny bags before keeping in godowns, warehouses, or stores.
3. Safe and Proper Storage:
Godown, warehouses, and stores should be properly cleaned, dried, and repaired. Pathways (alleys) should be provided between the stacks of grain-filled bags, for periodic inspection, spraying, or fumigation.
For the large-scale storage of grains, grain silos are used. The silos are big and tall cylindrical structures. They store different stocks of food items at different levels. Silos are provided with outlets (chutes) at different levels to withdraw the desired stock of grains. They have built-in arrangements for aeration, temperature control, protection from insects, rats, birds, and mammals, for fumigation and inspection of their grain stocks.
4. Chemical Control:
The pesticide solution is sprayed over the gunny bags containing food grains by using a manual sprayer or a mechanical sprayer. The spraying of pesticides is more suitable for disinfecting the whole godown before the arrival of the fresh stock of grains. The following pesticides can be sprayed BHC (benzene hexachloride), malathion, and pyrethrum. Pesticides can be mixed with the grains only when they are to be used as seeds for sowing.
Those pesticides which can destroy insects by forming toxic fumes are called fumigants and the process of their use is called fumigation. Fumigants may be solid, liquid, or gaseous. Ultimately they volatilise or react with the moisture of the air, forming poisonous fumes.
- Aluminium phosphate (solid fumigant) tablets commonly known as black poison (3g each) can be used at 2 tablets per tonne grain or 160 tablets per 100 cubic meter volume of grain.
- Ethylene dichloride plus carbon tetrachloride or EDCT (liquid fumigant). Ethyl dibromide (EDB) is another liquid fumigant.
- Methyl bromide (gaseous fumigant).
Fumigation is the most effective method of destroying insects in stored food grains.