Rice

Harvesting & Storage

Drying

• Drying of harvested paddy is necessary to maintain quality, minimize losses, and prepare the grain for storage and milling.
• It inhibits biological deterioration, prevents mould growth, fermentation, sprouting and discolouration of the grain.
• At low moisture content (13-14 per cent) the grain is relatively dormant and can be stored for longer periods.

Methods of drying

Sun drying

The effectiveness of sun drying depends upon temperature and relative humidity. Excessive losses occur due to scattering, birds, rodents, etc. This method is unhygenic.

• Each area has its own method of sun drying, depending on the peculiarities of customs, climatic conditions, varieties and labour supply.
• The simplest and most common method is to lay the cut plants in the road / field, in swaths or loose bundles, until the paddy is dried.
• In some places the partially dried plants are gathered after a few days and arranged in layers or heaps for a second drying.
• The second drying may also be done on drying floors or mats after threshing.
• Another is to thresh immediately after cutting and dry the threshed grain.

Problems

Sprouting, discolouration and microbial attack occur in cut plant drying. Breakage of grains.

Artificial drying

• In storage or bin drying
• Deep bed drying
• Thin layer drying
• Continuous flow drying

Storage - Principles

• Rice is stored as rough rice (paddy), brown rice and milled rice as such or with gases like carbon dioxide or nitrogen.
• It is stored underground or above ground, in elevated silos and under water.
• It is stored at normal temperature and at cold temperature.
• Under normal storage conditions grains are subjected to continuous physico-chemical changes which affect their culinary properties and nutritive value.

Intrinsic factors

Constituent of grain-tissue components and enzymes.

Extrinsic factors

• Physical : Moisture, temperature, oxygen concentration.
• Biological : Birds, rats, insects, mites, moulds, bacteria,
• yeast Engineering : Storage structures, handling equipments

Ageing

• Storage of rice (as rough rice, brown rice or milled rice) even under normal conditions brings about various changes, through the process of ageing.
• It is a natural and spontaneous phenomenon, involving changes in the physical and chemical characteristics of the rice that modify the processing, cooking, eating and nutritional qualities and affects the commercial value of the grain.

Storage Structures

• Storage of paddy at the village level represents a most vulnerable stage wherein loss of grains is recognized to be substantial.
• In rural areas, storage structures have been developed on the basis of traditional practices and experience.
• Locally available materials such as wood, bamboo, straw and clay are used for their construction.
• The storage structures vary in size and type in various regions.
• They are either spherical, cylindrical or rectangular in shape.
• In some places, grains are stored in underground and above-ground pits.
• Some are outdoor and some are indoor structures.
• Only grain for long-term storage is stored in these structures or containers.
• Grain for disposal and short-term use is kept in bags or heaped in a corner of the farmer’s house.
• Most of the traditional storage structures are not completely moisture-proof or air-tight.
• The platform on which the structure is built is not high enough, and rodents find easy access into the structure.
• In such structures the grain is usually damaged by insects, fungi and rodents.
• These structures are also not suitable for fumigation.
• Moreover, their life is short and frequent maintenance is required.
• The excessive heat, dampness and high relative humidity in the tropics are not only conducive to fast decay and deterioration of food grains but are also favourable for the growth and proliferation of insect pests and microorganisms.
• Paddy straw, husk, bamboo strips, palm leaves, wooden blanks and mud are the main raw materials for constructing indigenous structures.
• In recent years, structures built with baked or unbaked bricks, plastered with mud or lined with water-proof materials have started to come up.
• Progressive farmers have started using metal bins or structures with air tight lids having polythene sheet as a layer.

Underground cellar (Khattis)

• This type of storage is found in India at places where water level is low.
• The depth of a khatti is about 5 m and width of almost similar diameter upto a narrow circular opening at the top. It may or may not be lined with bricks or concrete.
• The grain is stored in bulk.

Mud bin (kudir)

• These are made of unburnt clay mixed with straw or dry grass with 2.5 cm to 8.0 cm thick wall and are of oval, rectangular or circular shape.
• A reasonably big hole is provided at the top for pouring the grains.

Thekks

In drier zones, gunny or jute cloth is used for making round storage structures, locally termed thekkas. Their capacity ranges from 10 to 80 q.

Straw bin (seru or puri)

• It is constructed with paddy straw bound in the form of ropes of 50-100 mm diameter.
• The structure is tapering, with lesser diameter at the bottom and more at the top.
• Usually dry threshed straw is used for making the ropes and freshly harvested or partly threshed straw is used for inside lining.
• The construction of the structure and loading is done simultaneously.
• The floor is made out of compacted earth and loose straw and raised to 150-300 mm height to prevent direct contact of paddy with the ground.
• The roof is made up of loose paddy straw to give a conical shape to prevent any rain water going into the structure.
• The capacity is 5 to 15 tonnes.

Kottai

• This is a straw storage structure which is constructed in the form of a large bundle, tightly secured by means of paddy straw ropes both horizontally and vertically.
• Sometimes it is plastered with cowdung.
• It is placed on a stone or raised platform in one corner of the house.
• The capacity varies from 50 to 100 kg.

Wooden storage structure (Patthayam)

• This is an indoor wooden storage structure, usually rectangular in shape. The construction of patthayam is in the form of trays.
• The bottom tray has sides as well as a bottom plank with open top.
• The rest of the trays do not have any bottom or top, but have only the sides.
• A 5 mm wooden strip is nailed to the top of all trays, the nailing is done in such a way that 25 mm portion extends beyond the tray.
• The roof is provided with a series of wooden planks to cover the entire width of the structure and they are nailed to the top tray.
• A sliding door or hinged door is provided for loading and an outlet is provided for unloading.
• The capacity of the structure varies from 0.5 to 3 tonnes.

Some commonly used modern storage structures are given below

Storage Pests

• The stored grains are mainly affected by insects, rodents and microorganisms.
• The insects cause damage by feeding on grains and contaminate the produce with their cast skin debris and faeces.
• Rats also cause considerable amount of damage by way of feeding and contamination.
• The insects can destroy approximately 10-15% of the produce.
• The following are the important pests that cause damage in stored paddy/rice.

Rice weevil

Note: + major, * minor, - Insignificant

Management of stored grain pests

• Maintain store house hygiene by brushing the cracks, crevices and corners, removing all debris and cleaning the entire godown before storing the grains to eliminate various biostages of pests.
• Reduce moisture content below 10% by drying to prevent the build up of pests
• Dry all the bags, bins, etc. in the sun to kill the insect biostages harboured in them.
• Eliminate conditions which favour storage pests by sieving and removing all broken grains, stitching all torn bags before filling.
• Treat the walls, dunnage materials and ceilings of empty godown with malathion 50 EC 10 ml/l or DDVP 76 WSC 7 ml/l @ 3 l spray solution/100 sq. m.
• Maintain good storage conditions by providing dunnage leaving gangway or alleway of 0.75 to 1 ml all around and at convenient intervals for aeration, inspection, prevention of moisture seepage and for fumigation and chemical spraying.
• Air charge or treat alleyways and gangways with malathion 50 EC 10 ml/l or DDVP 76 WSC 7 ml/l (1 l of spray fluid/270 cu.m)
• Apply stack spraying over the bags with malathion 50 EC 10 ml/l @ 3 l of spray fluid/100 sq. m.
• Draw samples at fortnightly intervals and based on the intensity of infestation, decide the need for shed fumigation.

Fumigation

• Decide the need for shed fumigation (entire store house or godown) or cover fumigation (only selected blocks of bags).
• Check the store house/godown and the black polythene sheets or rubberized aluminium covers for holes and get them ready for fumigation.
• Choose the fumigant and work out the requirement based on the following guidelines.
• Aluminium phosphide
• For cover fumigation: 3 tablets of 3 g each per tonne of grain.
• For shed fumigation: 21 tablets of 3 g each for 28 cubic metres.
• Period of fumigation: 5 days
• In case of cover fumigation, mix clay or red earth with water and make it into a paste form and keep it ready for plastering all round the fumigation cover or keep ready sand-snakes.
• Insert the required number of aluminium phosphide tablets in between the bags in different layers.
• Cover the bags immediately with fumigation cover.
• Plaster the edges of cover all round with wet red earth or clay plaster or weight down with sand-snakes to make leak proof.
• Keep the bags for a period of 5-7 days under fumigation based on the fumigant chosen.
• Remove the mud plaster after specified fumigation period and lift cover in the corner to allow the residual gas to escape.
• Allow aeration and lift cover after a few hours.
• Follow similar steps to ensure leak proof condition, fumigation period, aeration, etc. in case of shed fumigation.
• Fumigants are used for curative treatment and they have no residual action on new immigrant insects which can infest grain.
• Sample periodically and fumigate the stored material based on need.
• Handle fumigants with utmost care as per specifications.
• Prophlylactic treatment of grains/seeds:
• If the produce is meant for seed purpose, mix 1 kg of activated kaolin or malathion 5 D for every 100 kg of seed and store/pack in gunny or polythene lined bags.
• If the produce is meant for grain purpose, mix 1 kg of activated kaolin for every 100 kg of grain and store.

Note:

Never mix synthetic insecticides with grains meant for consumption.

Milling & Curing

Milling

• In the process of removing the husk from paddy, force has to be applied.
• More force is required during removal of various layers which make up the bran polishings.
• This inevitably causes breakage of some of the grains even in the best samples, and in bad ones it can break every grain.
• The yield of rice from paddy during milling is determined by three factors viz., The husk content of the variety, The degree of milling and grain breakage.
• The husk content of paddy varies from 14 to 28 per cent.
• Factors influencing milling breakage are harvesting stage, field cracks, nature of the grain, drying conditions, storage conditions, grain moisture, temperature, humidity at the time of milling, type of sheller and weather etc.

Curing

• Preference for rice palatability differs among different people. The differences in cooking quality between old and new rice relates to the lower swelling capacity of the latter and its tendency to yield a thick viscous gruel during cooking.
• To overcome the above defects in the freshly harvested paddy and to suit the taste of the raw-rice eating consumers of India, methods have been developed to hasten the ageing in fresh rice and this process is called ‘curing’.
• By directly steaming the freshly harvested paddy, its cooking quality can be improved. Steaming for 15-20 min was sufficient to bring about satisfactory ‘curing’ effect with regard to cooking quality.
• By sand roasting of freshly harvested paddy with 18 to 21 per cent moisture for 1 to 1.5 minutes at 95°C with a tempering of 1 to 2 hr, the ‘curing’ effect can be achieved. The new milled rice also can be ‘cured’.

Parboiling

By parboiling, the required hardness to grain is imparted. Partial cooking of grain with husk intact is termed parboiling.

Advantages

• Parboiling of paddy results in higher milling recovery, translucent kernels, greater nutrient status, easy hulling, less susceptible to insect attack during storage, higher oil in bran with better stability, less cooking loss, more swelling when cooked to the desired softness, and easy digestibility with high protein efficiency ratio.
• Parboiling is accomplished by soaking in cold, warm and hot water, by open or pressure steaming and closed heating or merely soaking at 70° or 80°C. A method for eliminating off-odour in parboiling process exists.
• Rice is gelatinized by alkali treatment. Brown rice can also be parboiled. Parboiling of paddy results in changes such as gelatinizing of starch, retrogradation of gelatinized starch or the solubilization of amylose and amylopectin fractions and their subsequent complexing and disruption of protein bodies.
• The degree and intensity of heat treatment during each step of parboiling process greatly influences the nature and extent of change in the end product. A multitude of processing variables (i.e. temperature range and duration of soaking etc.) exist in parboiling. Besides the above variables, the retention time of hot paddy and the manner of drying also influence the cooking and palatability characteristics of parboiled rice