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Post Harvest Management

Post Harvest Management
25
Aug

Uniform Drying

1. During the drying process there is always variability in moisture content of individual grains.

2. Especially in fixed-bed dryers the grains at the air inlet dry faster than at the air outlet resulting in a moisture gradient in the grain bulk at the end of the drying process.

3. For production of good quality grain or seed, this variability should be kept as low as possible.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Drying Rate/Temperature

1. Above 18 % moisture content, the grain drying rate can be increased by providing a higher temperature or more drying air without major changes in grain temperature.  

2. Below 18 % moisture content, increase in drying air temperature will not increase the drying rate but will increase grain temperatures and potentially damage the grain.

3. Therefore, higher drying air temperatures can be used to dry grain quickly down to 18% moisture content but lower temperatures should be used to remove internal moisture from the grain.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Falling rate period

1. As time passes, it takes more time for internal moisture to appear at the surface, and evaporation of water is no longer constant in time.

2. As a result, drying rate will decline, and some of the heat from the drying air will heat up the grain. 

3. For paddy grain, the falling-rate period typically occurs at around 18% grain moisture content.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Constant rate period

1. Once the grain is at the drying temperature, water starts to evaporate from the surface of the grain.

2.  During this period, all the heat from the drying air is used to evaporate surface moisture and the amount of moisture removed from the grain is constant in time.

3.  It is therefore called the constant-rate period. During this period, grain temperature is constant as well.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Pre-heating period

1. When wet grain is exposed to hot air, initially only a very slight change in moisture content is observed.

2. This happens because all the heat provided in the drying air is used to heat up the grain to the drying temperature.

 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

The drying process - Moisture Removal

1. In paddy grain, moisture is present at two places: at the surface of the grain, ‘surface moisture’, and inside the kernel, ‘internal moisture’. 

2. Surface moisture will readily evaporate when grain is exposed to hot air.  Internal moisture evaporates much slower because it first has to move from the kernel to the outside surface.

3. As a result, surface moisture and internal moisture evaporate at a different rate.  This difference results in a different ‘drying rates’ for different period of drying.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/the-drying-process
25
Aug

Equilibrium Relative Humidity

1. If the grain is stored in an enclosed storage environment, the air surrounding the grain if it is well sealed is not in free contact with outside air. 

2. In this case, the relative humidity of the enclosed air will reach equilibrium with the moisture content in the grain.  The final relative humidity of the enclosed air is often expressed by the ‘equilibrium relative humidity’.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/equilib rium-moisture-content
25
Aug

Equilibrium Moisture Content

1. The stored grain moisture content will be generally influenced by the temperature and relative humidity of the surrounding environment.

2. Protecting the grain during rainy season when there is high relative humidity in the air is very important it will leads to the grain quality deterioration. 

3. The grain moisture content of paddy stored in jute bags or clay pots will automatically increase in the rainy season to unsafe levels regardless of how well the grain was dried before storage.  

File Courtesy: 
http://www.edwardsgroup.ca/keho/keyconcepts.cfm?local=KeyConcepts
25
Aug

Reduced head rice yield

1. Major cause for fissuring of rice kernels is the moisture adsorption of individual dry grains with moisture contents below 16 %.

2. This can happen either when wet grain is mixed with dry grain or when dry grain is exposed to humid ambient air with a relative humidity higher than the equilibrium relative humidity at the corresponding grain moisture content. 

3. Fissures in rice kernels usually lead to cracking of the grain during the milling process and thus reduce the head rice recovery.

 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/grain-moisture-content-and-grain-quality
25
Aug

Loss of freshness/odour development

1. Deterioration of quality or aging of stored rice results from a combination of a change in the chemical components and changes of rice kernel characteristics. 

2. Heat build up in the grain (above 55ºC) due to insects, molds or high humidity will often lead to a musty odour in rice.

3. Therefore, rice stored for longer periods under adverse conditions can develop odours which reduce the market value of rice considerably. 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/grain-moisture-content-and-grain-quality
25
Aug

Loss of germination and vigour

1. Moisture in grain will gradually reduce germination ability of the seed during storage.

2. Active respiration of the grain during storage will deplete the nutrition reserves that the seed uses to germinate or sprout. 

3. Molds and diseases can also reduce the ability of the seed to germinate.

4. The lower the moisture content of seed at the beginning of storage, the longer the seed remains viable.

 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/grain-moisture-content-and-grain-quality
25
Aug

Discoloration/Yellowing

1.  Rice endosperm often develops a yellow

discoloration during commercial storage in conditions of high temperature and moisture, thereby reducing the value of the grain. 

2. This postharvest yellowing appears to be coincidental with fungal presence. 

3. Paddy discoloration is a complex biochemical process; it can be easily avoided by timely drying of paddy after harvest.

 

File Courtesy: 
http://cerealchemistry.aaccnet.org/doi/abs/10.1094/CC-82-0721
25
Aug

Insect infestation during storage

1. Field infestation, insects fly from stores to fields and lay eggs upon the maturing grains.

File Courtesy: 
http://www.ikisan.com/Crop20Specific/Eng/links/ap_maizeStoredGrainPests.shtml
25
Aug

Mold development during storage

1. Fungal deterioration of grain is a dynamic process that involves a succession of micro-organisms, the breakdown of organic matter to yield carbon dioxide and water, and the generation of heat (Bothast, 1978).

2. Nutrients are lost because of changes in carbohydrates, proteins, lipids and vitamins.

File Courtesy: 
http://www.protek-usa.com/PDF_Files/Heat20Build.pdf
25
Aug

Heat build up in the grain during storage

1. In commercial storage of rice grains the build-up of heat mainly because of the respiration of the wet grains and also the store grain pests.

2. Development of the heat results the   gradual deterioration of viability, nutritive quality, and end use properties during storage under commercial conditions.

File Courtesy: 
http://www.protek-usa.com/PDF_Files/Heat%20Build.pdf
25
Aug

Grain moisture content and grain quality

1. The total amount of moisture present

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/grain-moisture-content-and-grain-quality
25
Aug

Drying basics of paddy

1. Drying of grain involves exposing grain to ambient air with low relative humidity or to heated air.

2. This will evaporate the moisture from the grain and then the drying air will remove the moisture from the grain bulk.

3. Since drying practices can have a big impact on grain quality or seed quality, it is important to understand some fundamentals of grain drying.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics
25
Aug

Purpose of drying

1. The purpose of paddy drying is to reduce the moisture content of rough rice to a safe level for storage.

2. The rice crop is harvested at 24-26 % moisture content

3.These moisture has to be reduced to 12-13 % by drying Any delays in drying leads to yellowing, grain discoloration and build up of heat by mold growth.

4. Damage caused by insects that are more active at higher moisture content levels.

File Courtesy: 
http://www.fao.org/teca/content/rice-paddy-drying-systems
25
Aug

Paddy Drying

1. Drying is the process of simultaneous

heat and moisture transfer. 

2. It is the removal of excess moisture from the grains. Once dried, the rice grain, now called rough rice, is ready for processing.

3. Proper drying results in increased storage life of the grains, prevention of deterioration in quality, reduction of biological respiration that leads to quality loss of grains, and optimum milling recovery.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/introduction-to-paddy-drying
3
Jul

Carbon dioxide fumigation for control of rodents

1. Insects need oxygen for respiration. With carbon dioxide fumigation, much of the oxygen in the storage bin is replaced by carbon dioxide that suffocates, dehydrates and also produces toxic chemicals in the blood of the insects.

2. To be effective, elevated carbon dioxide levels must be maintained until all insects die.

3. The required exposure time depends on the percentage of carbon dioxide and the temperature of the grain. The cost of CO2 fumigation is high.

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/storage-pests/insects
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