Post harvest technology(Modern storage systems:)

Modern storage systems: 

Modern storage system can be classified into the following based on the type of storage structure or container, facilities for loading and unloading, and methods of controlling the storage atmosphere.

1. Bagged storage system

2.      Silo storage system

3.      Airtight storage system

4.      Aerated storage system

5.      Low temperature storage system

6.      Controlled atmosphere storage system

7.      Damp grain storage system with chemicals

Bagged storage systems:

Bagged grains are stored in flat warehouses which are known by the term “Conventional godown”. Public bagged food grain storage system includes local supply depots and central depots. The local and central depots are essentially for short-term storage of food grains. These food grains are either procured the farmers during harvesting season or received from other local and central storage depots, silos and imports for distribution to other local and central storage depots or rations shops.

One of the major disadvantages of the bagged storage system is that the reabsorption of moisture takes place during humid wet season especially in the outer layers of bags, and this accelerates biological activity in the food grain and results in deterioration and loss of the product. In the dry season when the roof and wall surface temperature is extremely high, the food grains stacked within one meter of the roof or close to walls become hot. This causes relocation of moisture which results in deterioration of grain during storage.

Silo storage system:

A silo is a storage facility in bins with provision for mechanical loading and unloading of the grains. A silo installation is known as “Elevator”, because it is equipped with elevator to take the grain up and down. This is made either of steel, aluminum or concrete. In concrete bins, the circular forms give the greatest strength vis-a–vis the material used for construction. Food grain can be stored for years in either metal or concrete silos with aeration and temperature detection facilities.

Aerated storage system:

In aerated storage system air is moved through stored grains for the primary purpose of maintaining a uniform moisture content and or temperature throughout the storage. It also limits activity of fungi on any damper areas, and reduces the rate of auto- deterioration of the grain.

Methods of preventing storage damage

Moisture and temperature control:

Under normal conditions storage of grain of moisture content below 14% and temperature below 200C gives reasonable protection from microbial, chemical and biochemical changes although insect and rodent damage can also occur.

Use of antimicrobial agents: Fungicides retards the growth of moulds but the major problems of using fungicide is that many of these will kill the grain, some are toxic to human and animals. Propionic acid and propionates are the most satisfactory fungicides for the use in grain.

Antimicrobial agents are not needed as aids to grain stability during storage because the moisture requirement of bacteria are usually well above grain moisture contents.

Fumigation:

Fumigants are very effective in preventing insect attack on grain. A widely used grain fumigant is ethylene dibromide. The potential problems in using fumigants include the danger of residues to the consumer and possible effects on grain properties.

Rodent control:

In some areas rodents are plague proportions and destroy very large amounts of cereals crops. Methods of rodent control need to recognize:

1. Predation by dogs, cats, foxes, mongooses, snacks etc.
2. Poisons, traps, gas.
3. Correct sanitations practice.

Oxygen-free storage atmospheres:

The absence of oxygen from storage atmosphere will assist in maintaining the quality of stored grain. This will retard grain respiration and kill or deactivate harmful organisms such as insects, moulds and rodents.

Chill storage:

Chill storage temperatures, below 100C, provide an excellent means of preventing grain deterioration during storage even when grain is stored at high moisture contents but it is costly.

Aeration:

This procedure consists of blowing air at ambient condition through the grain. The rate of air flow is usually o.o3-0.5 volumes of air per volume or grain per minute. Aeration greatly reduces risk of damage from insects, mites and fungi.

Post-harvest losses of grain crops:

Harvesting loss:    0.7%

Carrying loss      :  0.16%

Threshing loss   :   8.9%

Field drying loss:   0.31%

Cleaning loss      :  1.2%

Total loss            :  10-13%

Loss due to application of traditional method:

v  Harvesting loss: due to shattering, harvesting of immature grains, attack of rodents and birds

Prevention: harvesting to be done early in the morning or late of afternoon; use of improved serrated sickles; measures against rodents, birds etc. shattering loss may be prevented by using containers/bags to transports crops.

v  Threshing loss: due to un-threshed grains, scattering of grains. Stacks grains before harvesting need to be protected against rodents, birds, domestic animals.

Prevention: Threshing should be done on hard surface ‘care is needed to prevent breakage during threshing. Pedal or mechanical thresher should be used. Threshed grains should be protected from sudden rain by covering, rodents, birds, insects, and domestic animals.

v  Loss during cleaning: through spillage, incomplete separation from materials, loss of sound grains with other materials.

Prevention: use of ground spreads, hard, smooth and crack-free floors; use mechanical winnower, avoid winnowing against strong wind.

v  Drying of grain:

Immediate after harvest or cleaning, to moisture content of about 12%

Objectives: to prevent germination of seeds, to retain maximum quality of grain, to reach safe level of moisture to prevent growth of fungi and bacteria. Sun drying or mechanical drying: use of black polyethylene reduces drying time.

Storage: stored at farm level, trader storage and Govt .storage. Farmer retains some portion of the grain for home consumption, seed and payment of labour. Trader/Govt. storage: Market demand, shortage, famine, fluctuation of prices.

v  Storage loss: due to insect, rodents, microorganisms.

Nature of loss during storage: weight loss, quality loss, loss in nutritional value, hygienic deterioration.