Drying is a process which reduces moisture content from grain to safe limit. Drying process is basically the transfer of heat by converting the water in grain to vapour and transferring it to the atmosphere. Threshed paddy or boiled paddy required drying. It is essential that drying is gradual and slow in the initial stages in order that the milling quality is not adversely affected. When paddy is relatively dry, it can be dried further rapidly without damaging the grains. High moisture in the grains as well as high humidity in the atmosphere cause sprouting and molding of grain. This problem can be overcome by mixing powdered common salt at 5 Kg/100 Kg of grain. The salt absorbs water from the grain and salt solution flows out of the heap of grain. This treatment prevents heating and subsequent damage to the produce. Another way of storing wet paddy is by mixing paddy husk, which helps in storage for about seven days. Artificial drying by using the steam to dry the produce, can be done at any time of the year, but is expensive. Timing Dry paddy as soon as possible to 18% moisture content to decrease discoloration, spoilage and sprouting. Moisture content target Do not dry below 14% MC - unless for long term seed storage - over dried grain will crack upon readsorbing moisture from the atmosphere and thus will have a lower head rice recovery when milled. Do not mix grain of different moisture contents as this causes moisture absorption by the dry grain and results in grain cracking. Drying temperature and rate Set operating temperature initially at 150ºF (65ºC). As the grain dries out, or when moisture has dropped to 18%, turn down drying air temperature to 110ºF(43ºC) to prevent fissuring of the grain. At 65ºC, the drying rate is about 1% moisture per hour. At 43ºC, the drying rate is about 0.5% to 0.75% moisture per hour. If there is no great urgency, fuel costs can be reduced by using ambient air (if relative humidity is less than 70%), once the grain moisture has reached 18%. Then, slow dry the grain with ambient air until moisture reaches 14%. Drying Options - flat bed dryers, recirculation dryers, sun drying. Drying is done either by using : Solar energy or by Artificial heating. Sun Drying Sun-drying is carried out by the farmers on public roads or on made-up floors under uncontrolled conditions. Rice millers invariably use concrete floors for drying. Such drying results in sun-cracks and contamination on quality of rice is little realised as much of the milling is in hullers which by themselves contribute to breakage. Dependence on sun for drying also means break in operations when sun is not available. In case of sun drying the produce is spread on hard floor or threshing yard around 10-cm thickness, and is allowed to dry by heat supplied by the sun. If high moisture continues to remain in rice after harvest, it would undergo spoilage because of high temperature, respiration rate and microbial activity, and the presence of foreign matter. Hot spots often develop in concentrations of foreign material In general, four to five days of sun drying is required for different produce to bring the moisture to a safe level. In tropical regions, one-day drying under full sunshine throughout the day brings down grain moisture content of rice from 24 per cent to 14 per cent. Though sun drying is cheaper, there are some problems. The grains that are in the upper layers develop fissures due to uneven sun-drying resulting in broken grains. However, this problem can be overcome by repeated stirring. Artificial Drying methods Flow drier heated by paddy husk. Batch drier heated by either furnace oil or paddy husk. Mobile driers heated by paddy husk. Unheated air drier. Portable driers is a recent development. Bagged raw paddy or paddy in bulk can be dried with these driers by keeping the air temperature at 55º-60ºC. It takes about 1 hour for reducing the moisture by 2 per cent from 22 per cent and later on one hour for every one per cent. The driers being portable, handling and transport costs are considerably reduced. Avoid grain from overheating. Drying for seed Timing Dry paddy to 18% moisture content as soon as possible (especially during periods of inclement weather, and when grain has moisture above 21%) to decrease discoloration, spoilage and sprouting. Moisture content do not dry below 14% MC - unless for long term seed storage - over dried grain will crack and re absorb moisture from the atmosphere and thus will have a lower head rice recovery when milled. Drying temperature and rate Drying at 110ºF (43ºC) The drying rate of a flatbed dryer is about 0.5% to 0.75% moisture per hour. If the initial moisture content is 21%, it will take about 10 to 14 hours to dry the grain to 14%. Dry the grain continuously until moisture of grain near the blower end of bin has reached 14%. If blowers are delivering the correct air volume, it is not necessary to mix the grain. However, more uniform drying can be attained if the grain is mix at least once, halfway during the estimated drying period. Monitor the drying progress with a moisture meter. Drying options Flatbed dryers, recirculation dryers, sun drying Seed purity : Maintain genetic purity by preventing mixing or contamination with other seeds. Clean and grade seed to produce uniform sized seed grains. Storage : Store seed and protect it, if necessary from bacterial and fungal growth, and infestation by mites and insects with the proper seed protection chemicals. Hygeine about the seed storage area is critical.

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