Storage

 

 

 

 

Equilibrium moisture content

 

 

 

 

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Describe the importance of having the right moisture content in stored rice.

 

 

 

 

 

 

 

Equilibrium = 'balance' or 'stability'

What is the 'Equilibrium Moisture Content'?

As mentioned before, rice grains absorb moisture from the air surrounding them. In storage, the final moisture content of rice depends on the temperature and relative humidity of the air around the grain.  

 

The grain will continue to absorb moisture until it reaches an equilibrium with its environment. The final grain moisture content you get in storage is called the ‘equilibrium moisture content’ or EMC.  

 

 

 

Storing rice in tropical countries is difficult because of the high temperature and humidity

The moisture content of grain depends on the temperature and the relative humidity of the surrounding air

 

The following table shows the EMC of paddy under different storage conditions.

 

Yellow colored areas = good humidity and temperature for storing rice in a tropical climate.

 

If grain is not protected against humidity in the air, in particular in the rainy season when the relative humidity may reach 95%-100%, grain moisture content will rise. This will give lower quality rice.

 

Equilibrium Moisture Contents (EMC) of paddy at different storage temperatures and Relative Humidity

 

 

 

 

What is 'Equilibrium Relative Humidity'?

If the grain is stored in a sealed storage environment (bag, silo, etc), the air around the grain is not in direct contact with the air from outside.  In that case, the relative humidity of the enclosed air will reach an equilibrium with the moisture content in the grain.  

 

The final relative humidity of the enclosed air is often expressed by the 'equilibrium relative humidity'.

 

Grain you store must be well dried. If the moisture content of the grain is not low enough you will have grain losses:

 

 

What should be the relative humidity inside the storage?

 

In general, an equilibrium relative humidity inside the bag, bin, silo or any other storage should be 65% or less. A relative humidity of 65% or less is considered a safe prevention against the development of molds.

 

 

Remember: The longer you need to store the grain, the lower the moisture content must be

 

Storage period

Required MC for safe storage

Potential problems

2 to 3 weeks

14 - 18%

Molds, discoloration, respiration loss

8 to 12 months

13% or less

Insect damage

More than 1 year

9 % or less

Loss of viability

 

 

 

Measuring  moisture content (MC) by using a  moisture meter

There are many different types of grain moisture meters.  Make sure your meter is suitable for paddy grain.

 

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

 

 

 

 

 

 

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Up next is a quiz about this module.