Post production: Drying

 

 

 

 

 

Sun drying

 

 

 

 

 

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Describe how to properly sun dry

 

 

 

Dry with the help of the sun

 

What is sun drying?

 

Sun drying is the traditional method for reducing the moisture content (MC) of paddy. With sun drying, the grains our spread out outside in the sun. The sun heats up the grains and also the surrounding air. This causes the water to evaporate from the grains, which makes the grain dry.

 

The warmth of the sun dries the grains

 

Cheap and good for nature

 

What are the benefits and limitations of sun drying?

 

Sun drying

Benefits

Limitations

  • Sun drying is cheaper than mechanical drying.

  • Sun drying is friendly to the environment.

  • You can not sun dry when it rains or after dark

  • Sun drying is a lot of work and you can only do a limited amount of grain

  • It is difficult to control the temperature. If the grains get to hot they will crack (during milling)

 

 

 

 

 

 

 

What are the sun drying methods?

 

Field drying should be avoided

 

1. Field drying

 

 

 

 

Field drying often happens if the farmers needs to wait for the thresher.

There is not enough air circulation to dry properly and at night the grain often gets wet again from the soil and the wet straw.

This causes fast grain deterioration so it should be avoided.

 

Need more information?

In field drying the rice plants are often stacked in piles with the panicles inside to protect them from rain, birds and rats.

Because of this, it becomes very, very hot inside the stacks.

  • Molds will grow quickly and infest the grains.

  • Discoloration of the grain will happen within the first day of field drying.

  • Also the relatively dry grains often absorb water from the straw which is more wet. This will make the grains crack, giving less head rice after milling.

 

 

Traditional, small-scale methods for individual farmers

 

2. Panicle drying

 

 

 

The panicles are tied in bundles and placed on pavements or mats or hung from frames. 

There is uneven drying because the grains on the outside dry faster than the grains on the inside.

 

 

 Medium-scale method for farmers, groups, and contractors.

 

3. Drying on mats or canvas

 

 

 

This is the cleanest method. The grain can be easily mixed and quickly collected  when dry.

It asks for some small financial requirement as you need to buy the mat or canvas (plastic).

 

 

4. Pavement drying

 

 

If you have a pavement you can do pavement drying. It is cheap but grain can easily mix with stones and dirt. You might need tools to mix the grain.

Sun drying:

Spread!

Mix!

Protect!

 

 

 

 

 

 

 

 

 

Important: Monitor the drying process!

Check the temperature: When drying, the grains should never be warmer than 50°C or 42°C for seed.

Check the Moisture content: The moisture content should not decrease faster than 1% per hour. The final moisture content should be 13-14% for grain and 12% for seed.

 

 

 

 

How to use an IRRI moisture meter?

 

Measuring the moisture content of the grain is very important to ensure proper drying. To measure moisture content you need to have a moisture meter. IRRI developed a cheap moisture meter that can be ordered at IRRI.

If you would like to see a short video on how to use the IRRI moisture meter then click on the play button.

 

 

Next lesson

 

Let's have a look at mechanical drying systems.