The importance of grain storage as part of the marketing, distribution and food security system is well recognized. In 1978, following the resolution of the UN General Assembly which called for the reduction of post-harvest losses, FAO launched the Special Action Programme for Prevention of Food Losses (PFL). Since then more than 250 projects have been implemented worldwide under this programme. During recent years, as a result of privatization and liberalization of trade, the organization and management of grain storage has changed in many developing countries.
GRAIN STORAGE PRINCIPLES
High temperature and high moisture affect grain quality in storage and cause rapid decline in germination, colour, oil composition, and many other characteristics. Insects and fungus impair the quality of grains directly by their feeding and development, and indirectly by generating heat and moisture. High temperature and moisture favour development of insects and moulds. Insects cannot develop at temperatures below 10°C and moisture below 9% in cereals.
If the moisture is very high the grains should be dried before long term storage. Hot-air drying is necessary to maintain the quality of high moisture grain. However, holding grain at too high a temperature for too long in the dryer will reduce grain quality.
Stored grains should be inspected frequently. By operating the aeration system and smelling the air coming through the grain, storage problems can be detected. Insect activity can often be detected by looking for powdery material under the grain.
RURAL STORAGE
In India, about 70% of farm produce is stored by farmers for their own consumption. Farmers store grains in bulk using different types of storage structures made from locally available material. The major construction materials for storage structures in rural areas are mud, bamboo, stones and plant materials. They are neither rodent-proof nor safe from fungal and insect attack. Some of the major considerations for constructing a storage structure to minimize losses are:
- The structure should be elevated and away from moist places in the house.
- As far as possible, the structure should be airtight after loading and unloading.
- Rodent-proof material should be used for construction of rural storages.
- The area surrounding the structure should be clean to minimise insect breeding.
- The structure should be plastered with an impervious clay layer to prevent attack by termites and other insects.
Jute bags
Buying agencies often collect the bagged grain from the farm or market and the producer has to store the sacks of grain for some time before they are sold. The bagged grain must be kept off the ground to prevent seepage of water or attack by termites. If there is risk of rain during the temporary storage period the bags should be covered with waterproof sheeting. Alternatively, the sacks of grain should be stacked waterproof sheet away from walls in a rodent proof room. Plastic sheet lined jute bags have added advantage of being both insect and moisture proof and are now preferred.
Storage baskets
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 are usually constructed entirely out of locally available plant materials: timber, reed, bamboo, etc. elevated at least one metre above ground level.
Peri for grain storage in Himachal Pradesh
Food grains like maize, wheat and paddy are stored in special structures made of bamboo called Peri or Peru. Prior to use, these structures are plastered on the inner side with a mixture of cow dung and clay. These containers are placed on the ground floor and grain is loaded into them from a hole made on the roof of the first floor. To take out grains, as per need, a special opening is provided near the bottom.
The use of bamboo containers allows the free exchange of gases inside the grain and keeping containers on the ground floor ensures cool temperature for storage. Loading from top and unloading from bottom offers easy material handling. Keeping storage structures away from main living room protects grain from fire etc.
Coal Tar Drum Bin
This bin was developed at the Central Institute of Agricultural Engineering (CIAE) and compares very well with other metal structures. Basically it is a used or empty bitumen drum, which is heated on fire to remove excess tar. A layer of tar remains inside, and serves as an insulator as well as a protective coating for the galvanised iron sheet. At CIAE the local artisans have been trained to fabricate these bins to suit village requirements. Inaccessible to rodents, efficient against insects, sealed against entry of water, these drums make excellent grain containers.
Chittore Stone Bin
As described earlier, locally available materials should, wherever possible, be used in the construction of grain bins. In Rajasthan, stone slabs are naturally available in abundance. At the College of Agricultural Engineering, Udaipur, a stone bin called the Chittore bin has been developed by using 40 mm stone slabs. It is a rectangular bin of 250 kg capacity and is constructed by farmers themselves using mud as a cementing material.
Polyethylene-lined bamboo bin
Conventionally, the bamboo bin fitted with a lid and with a plastering of mud inside and outside is a very common storage structure used by farmers in India. They are not impervious to attack by insects and rodent pests. The modification of these bins by lining them with polyethylene has been found to be very effective. One such bin, developed at the College of Agricultural Engineering, Akola, can store about 500 kg of grain. The bin is mounted on a metal tripod with rat barriers. It ensures air tightness due to the constant pressure of grain.
Underground Storage in Khattis
Practiced in northern India this method of storage is used in dry regions where the water table does not endanger the contents. They are long term storage pits of varying capacity from a few hundred kg to 200 tonnes. The entrance to the pit may be closed either by heaping earth or sand on a wooden board cover, or by a stone sealed with mud.
The advantages of khattis are:
- Few problems with rodents and insects.
- Low cost of construction.
- Ambient temperatures are relatively low and constant.
- Being indoors and invisible it is relatively safe from thieves.
- No need for continuous inspection.
The disadvantages are:
- Construction and digging are laborious process.
- Storage conditions adversely affect the germination capacity of grains.
- The grain can acquire a fermented smell after long term storage due to humidity.
- Removal of grain is laborious and can be dangerous because of the accumulation of carbon dioxide in the pit.
- Inspection of the grain is difficult.
- Risk of penetration by water, insects and rodents is high and the grain at the top and in contact with the walls often becomes mouldy.