Equilibrium moisture content (EMC)

 

What is the 'Equilibrium Moisture Content'?

As mentioned before, rice grains absorb moisture from the air surrounding them. The grain will continue to absorb moisture until it reaches an equilibrium or a balance with its environment. That final grain moisture content is called the ‘equilibrium moisture content’ or EMC.  

In (non-hermetic) storage, the final moisture content of rice will depend on the temperature and relative humidity of the air around the grain.  

 

The following table shows the EMC that paddy will get under different storage conditions.

 

The yellow colored area indicates the right grain moisture content of 13-14% in relation with humidity and temperature

Moisture content of paddy at different storage temperatures and Relative Humidity

 

With the help of this table we can work out if paddy with a certain moisture content is safe for (non hermetic) storage with a certain temperature and relative humidity.

 

 

 

What is 'Equilibrium Relative Humidity'?

 

If stored grain is not hermetically sealed then the air humidity, in particular in the rainy season, will quickly affect the grain moisture content.

 

However, 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'.

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.

Hermetic storages

 

  

 

Remember: Grain you store must be well dried. The longer you need to store the grain, the lower the moisture content must be. (see table)

 

You want to store for

The MC for safe storage is

2 to 3 weeks

14 %

8 to 12 months

12% or less

More than 1 year

9 % or less

Moisture content is measured with 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 here.