Storage of food grains

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In India, about 70% of farm produce is stored by farmers for their own consumption. Farmers store grain in bulk, using different types of storage structures made from locally available materials. The pre-treatment necessary for better storage life is cleaning and drying of the grain, but storage structure design and its construction also play a vital role in reducing or increasing the losses during storage. Storage losses constitute a major share of food grain loss in postproduction operations (Fig. 13).

When scientifically constructed storage structures are available, it is essential that the grain being loaded is of good quality. Therefore, the grain is cleaned to remove impurities, fungus infestation, and rotten seeds, and then dried to a safe storage moisture level. The present trend is to harvest the crop at a high moisture content. Therefore, grain moisture is generally twice the safe limit at the time of harvesting. Oilseeds and vegetable seeds are harvested at 3-7 times higher moisture than their safe storage moisture content. The safe storage moisture limits for major food grains are given in Table 1.

Fig. 12. CIAE multi-purpose dryer (dimensions in mm).

Storage Structures at Farmer Level

The major construction materials for storage structures in rural areas are mud, bamboo, stones, and plant materials. They are neither rodent-proof, nor secure from fungal and insect attack. On average, out of a total 6% loss of food grain in such storage structures, about half is due to rodents, and half to insects and fungi. Some of the major considerations in building a storage structure to minimise losses are:

Various research and development organizations in India have identified some proven, age-old structures from certain areas of the country and based on these, some improvised storage structures have also been developed and recommended for use at farmer level.

Fig. 13. Diagrammatic representation of percentage losses of wheat, paddy, pulses, and all food grains at various stages in the postharvest chain.

Coal Tar Drum Bin

This simple device (Fig. 14) has brought a major change in the storage system at farmer level. Farmers showed little resistance to this technology, mainly due to its low cost and easy availability. It 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. After the road construction authority has used the coal tar, the drums are discarded as junk or are sometimes used for protecting roadside plantations. The drum is heated by open fire to remove any excess tar. A layer of tar remains inside, and serves as an insulator as well as a protective coating for the galvanised iron sheet. The local artisan can bring this drum to an attractive shape and can also fabricate a lid and a discharge chute. A drum to hold 150 kg of cereal costs about $A11.00 (us 110/-), whereas a metal bin of the same capacity costs about $A35-40. depending on the thickness of the galvanised iron sheet used. At CIAE the local artisans have been trained to fabricate these bins to suit village requirements and have thereby generated gainful employment for themselves.

Fig. 14. Coal-tar drum bin (150 kg capacity) (dimensions in mm).

Domestic Hapur Bin

The Indian Grain Storage Institute, which is engaged in the development and dissemination of advances in storage technology to users, has developed metal bins for domestic storage of food grains (Fig. 15). They are made of galvanised iron and/or aluminium sheets. The bins are available from 200 to 1000 kg capacity and cost $A35.00 to $A120.00 (Rs 350-1200) per bin.

Fig. 15. Hapur bin (200 kg capacity) (dimensions in mm).

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 and abundant. At the College of Agricultural Engineering, Udaipur, a stone bin called the Chittore bin has been developed using 40 mm stone slabs. It is a rectangular bin of 250 kg capacity and is constructed by the farmers themselves using mud as a cementing material.

Double-Walled, 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. It provides employment to a particular community in rural areas who are trained in making these bins. The average life of a bin is about three years. They are not impervious and are prone to attack by insect 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 and it costs about $A22.00 (Rs 220/-). The only additional cost incurred is for the polyethylene and metal parts introduced in the modifications. The bin is mounted on a metal tripod with rat barriers as shown in Figure 16. At the discharge end, the use of a metal cone has made unloading very easy without spillage of grain. It ensures airtightness of the opening due to the constant pressure head of grain (Chouksey 1984).

Table 1. Upper limit of grain moisture content for safe storage.

Commodity Moisture content (% wet basis)
Paddy, rice (raw) 14
Rice (Parboiled) 15
Wheat Kabuligrun, Bengal gram 12
Sorghum, maize, barley, ragi, bajra, pulse, turmeric, wheat atta maida besan 12.5
Coriander, chillies 10
Groundnut pods 6-7
Mustard seed 5-6

Source: Agricultural Engineering Directory, 1983.

On-farm food grain storage

Farmers need storages of 1-4 t capacity to store grain. If the storage time is short (2-3 weeks) a flexible PVC sheet covering (30-50 micron size) known as a crop umbrella is used. Sometimes tarpaulins or large canvass sheets are also used to protect the grain, especially at night to avoid the surface layer of the grain becoming moist with dew. However, for 2-3 months storage periods, the bin developed at the Indian Agricultural Research Institute (IARI) is the most suitable. It is a LDPE (low density polyethylene) sandwiched bin, popularly known as Pusa bin.

It is worthwhile explaining here the detailed construction procedure of the Pusa bin which can be widely adopted not only in India but in several developing nations. Except for the LDPE which is purchased by the farmer, the bin is made with mud. The performance of this bin is similar to any other metal or concrete structure. In fact, because of the good insulation properties of the mud bricks used for construction, the problem of moisture migration during storage is minimal in the Pusa bin. About 9.5 million tonnes of food grain are stored in such bins in India (IPCL 1985).

Fig. 16 PKV Akola bin

Method of Constructing Pusa Bins

The bin is constructed on a hard surface to prevent rodent attack (Fig. 17). If the surface is not hard, a platform of burnt bricks is built. The black LDPE film (700 gauge) is spread over the platform, extending 60 mm from all four sides. Another platform of unburnt bricks is constructed ova the LDPE layer. The inside wall is built to the required height, depending on the capacity of the structure. The surface of the wall is plastered with mud.

A wooden frame with an additional pole at a distance of 450 mm from the end of the structure is prepared and is placed at the top of the inner wall to support the roof. An additional pole is placed 250 mm from the outer side of the structure to provide further support. A small hole, 90 mm in diameter, is cut at the bottom in the middle of the front wall for delivery of the grain. A mud slab, 50 mm thick, is placed over the raised inner wall to serve as a roof, leaving a manhole of dimensions 500 x 500 mm at one comer. The structure is then plastered with mud on top and on all four sides, and is left to dry well. An LDPE film cover of 700 gauge black sheet made in the form of a mosquito net is then placed over the dried structure.

At this stage, a pouch made out of galvanised iron or plastic pipe 90 mm in diameter with a cap, is fitted into the delivery hole. The LDPE cover is pulled down to meet the extending portion of the earlier layer on the platform. The edges of both the films are heat sealed. A small hole is cut in the LDPE cover to accommodate the exit pouch and the pouch is pulled out through this hole. A little soft wax is applied around the pouch touching the LDPE film to make the portion completely airtight. The LDPE film covering the manhole is cut diagonally.

Fig. 17. Construction details for Pusa bins.

The outer wall of the structure is erected using burnt bricks up to 450 mm and unburnt bricks for the rest of the portion. Alternatively, a band of metal is provided at 450 mm to make it rodent proof. The whole structure is again plastered with mud on top as well as on all four sides and allowed to dry before use.

After filling the structure with grain, the diagonal cut on the film covering the manhole is sealed with adhesive tape and the manhole is plugged with mud. For efficient performance, the Pusa bin is used only after it is completely dried and filled completely so that minimum free space is left The bins can be made of various capacities. The quantities of raw materials required for construction of a Pusa bin are given in Table 2.

Bulk storage of food grains in India

The grain is stoma in bull: mainly by traders, big farmers, cooperatives and government agencies such as the Food Corporation of India (FCI). The available storage capacity of these sectors is of the order of 18.55 million tonnes which is about 12% of total production and 41% of surplus (i.e. 30% of total production) production which comes to market for sale. The main agencies storing surplus grain, and the amounts involved, are as follows:

There are many kinds of storage systems followed depending on the length of storage and the product to be stored.

Cover and Plinth Storage

This is an improvised arrangement for storing food grains in the open, generally on a plinth which is damp- and rat-proof. The grain bags are stacked in a standard size on wooden dunnage. The stacks are covered with 250 micron LDPE sheets from the top and all four sides. Food grains such as wheel, maize, gram, paddy, and sorghum are generally stored in CAP (cover and plinth) storage for 6-12 month periods. It is the most economical storage structure and is being widely used by the FCI for bagged grains.

Community Storage Structures

Bulk storage structures of higher capacity, ranging from 25-100 t are termed community storage structures (Birewar 1985). They are made from reinforced bricks, corrugated galvanised sheets and aluminium sheets in capacities ranging from 25 to 57 t.

Rural Godowns

The rural godowns are primarily meant for providing warehousing facilities to the farmers. The godowns are of 100 to 1000 t capacity. They are owned by FCI, central and state warehousing corporations, market committees, or cooperatives looking to the need for having storage structures or facilities for agricultural produce. The Government of India (GOI) appointed an expert committee (1979-1980) which concluded that there was a need for storage facilities for 2 million tonnes of food grain. The GOI, keeping in view these recommendations, has given a 50% subsidy for the construction of rural godowns. Therefore, godowns are being constructed on a large scale in Indian villages.

Table 2. Raw material requirements for construction of Pus bins.

S1 Capacity Internal dimension (mm) Quantities of material required
No. (t) L B H LDPE film (mē) No. unburnt bricks No. burnt bricks
1. 0.5 610 610 1360 8.1 800 80
2. 1.0 840 840 1400 1 1.7 900 95
3. 2.0 1400 1000 1600 15.3 1150 100
4. 4.0 1720 1520 1600 20.9 165 210

Source: IPLC report on plasticulture 1985.
Large-Scale Modern Storage Structures

Silos are being used on a large scale for bulk storage of oil seeds (soybeans) and cereals by the Oil Federation of India and FCI. Bulk storage has advantages over bag storage, as follows:

The silos are either metal or concrete. Metal silos are cheaper than the concrete ones by 1520% depending on their size. The difference is more in small capacity units, e.g. 200 t (Fig. 18).

Generally, the silo system is equipped with other preparatory units like cleaning and drying equipment. Comparison of godown and silo systems of 10 000 tonnes storage capacity, as detailed in Table 3, indicates that under Indian conditions the silos are initially 50% more expensive than a godown system, but that this additional cost should be recovered within 2 -4 years and thereafter a saving of $A100000 - 190000 (Rs 1-1.9 million) per annum can be realised. The loss due to moisture is only 0.2% compared with 1% in the godown system. The loss caused by rodents, insects, fungi, and handling is as high as 8% in the godown system, compared with only 0.2% in the silo system (Sawant 1984). A grain saved is a grain produced and the adoption of such structures has been taken up by the government through cooperatives and various storage organisations in the country.

Fig. 18. Relationship between capacity and cost of storage.

Standards for Storage Structures

To achieve uniform performance from any structure, it is essential that the construction material and the method of construction should conform to a predetermined standard. The same applies in the case of storage structures, and for this purpose the Indian Bureau of Standards, New Delhi, has devised standards after careful examination of the storage needs. The standards followed for storage structures are listed in Table 4. In order to minimise losses during storage, users are exhorted to adhere to these standards during construction.

Table 3. Comparative costs for silo and godown storage.

Item Silo system Codown system
  (Rs.*) (Rs.)
Capital costs    
Land 20 000 60 000
  (1850 mē) (5550 mē)
Construction 6 500 000 3 940 000
Total 6 500 000 4 000 000
Recurring costs/year: grains/year For grain-1 year For oilseeds 4 6
of storage months storage
Loss due to moisture 40 000 (0.2%) 200 000 (1%) 100 000 (0.5%)
Loss due to rodents, insects, fungi, and handling 40 000 (0.2%) 1 600 000 (8%) 800 000 (496)
Operational costs
Electric power 27 500 80 000 40 000 (Fumigation)
Fuel for dryer 37 500 25 000 25 000 (Manual handling)
Total 145 000 1905 000 965 000

Source Sawant (1984)
*Conversion rate adopted: $Aust.1 = 10 Indian Rupees.

Conclusions

India produces about 150 million tonnes of food grains per year. Production has been steadily increasing due to advancement in production technology, but losses have remained static at 10%. This means that the loss of food grains is also increasing with the increase in food production. The main reason for this is improper storage, and an average of 6% out of a total 10% loss takes place during storage of food grains.

For scientific storage, drying of food grains to a safe moisture level is a top priority. In India there are about 35 000 dryers in the rice and pulse milling industry, but all of them are used to process the grain. The use of dryers to dry surplus grain kept for storage is not common. The main reasons for this are a lack of awareness among the rural populations, high capital cost, and no incentive given for farmers to produce properly dried grain. An immediate answer to this problem would therefore be to develop and select a proper size of dryer which is simple in construction and operation, and lower in cost.

Setting up a community drying-cum-storage complex as suggested by Ojha (1984) has great potential as it will help to reduce losses and to provide a better return for the grower. The types of dryers suitable for this level are identified and described. They need to be popularised among potential users.

Another area where the dryer indirectly plays a very vital role is at cottage level industry. A new concept in dryer design, i.e. tray-cum-LSU dryer developed at CIAE, has been described in this paper. The dryer can prove a backbone for rural industry, as the same unit can be used for drying the grains as well as processed food products by changing the trays.

Storage of grain in India is done at many levels. The major production is stored at farmer level and the root cause of massive storage loss lies here. The suitable low-cost structures developed have been identified.

On-farm storage is also important as it stores the surplus for a short duration and appropriate structures are explained with design features and construction procedures. Large-scale structures like silos and organizationally maintained structures are also explained. The use of dryers and scientific storage practices, if followed, can reduce the loss by about 6% and this will save Rs 13 500 million ($A1350 million) every year, and make available an additional 9 million tonnes of grain to feed the people.

Acknowledgment

We gratefully acknowledge the help extended by

Mr Zackaria V. John for typing the manuscript and

Mr Vijay Natekar for making tracings of the dryers and structures.

Table 4. Indian standards for storage structures and storage management.

S1 No. IS Number Title
1. IS 607-1972 Bagged food grain storage structures
2. IS 8453-1977 Bins, earthern, polyethylene embedded for bulk storage of food grains
3. IS 7715-1975 Bins for safe storage of food grain, method to test suitability of.
4. IS 600-1955 Code of practice for 'Bukhari' type food grain storage structure
5. IS 5826-1970 Flat storage structure for food grains (cap. 200 t)
6. IS 6201-1971 Flat storage structure (100-200 t)
7. IS 601-1955 Code of practice for construction of Kothar type rural grain storage structure
8. IS 602-1969 Silos for grain storage (Part I) construction requirements
9. IS 5503-1973 Part II-Grain handling equipment and accessories
10. IS 7174-1973 Steel bins for domestic storage (Part I)
11. IS 5606-1970 Steel bins for grain storage
12. IS 6151-1971 Part lI-General care in handling and storage of agricultural produce
13. IS 603-1960 Underground rural food grain storage structure

Source Agricultural Engineering Directory 1983

References

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