Measuring moisture content

Moisture content (MC) is the weight of water contained in paddy or rice expressed in percent. MC is usually referred to the wet basis meaning the total weight of the grain including the water (MCwb). For research moisture content referred to the dry matter of the grain is sometimes used (MCdb).

Why is measuring the moisture content important?

postproduction-moisture-meter

Accurate moisture content testing is important in managing and marketing paddy and rice because depending on the purpose rice has different ideal moisture contents. Inaccurate moisture content measurements lead to:

  • Extra drying cost and harvesting loss if paddy is harvested wetter than necessary
  • Spoilage if the grain is too wet in storage
  • Extra drying cost and loss of quality if paddy is dried too far
  • Lower head rice when milled at wrong MC
  • Weight loss (loss in profit) if grain is sold too dry

How to measure moisture content

Moisture content of grain can be measured by using either:

  • primary method, based on weight measurements like the (a) oven method or an (b) infrared moisture balance or
  • secondary method, using an electronic instrument that uses electrical characteristics of the grains.

Many different types of portable grain moisture meters can be used to measure the moisture content. When selecting a meter, make sure it is suitable for harvesting paddy or milling grain, depending on which activity you are doing. 

Read: Types of portable moisture meters

The following table summarizes the target moisture content for each of the key postproduction operation:

Operation

Desired moisture content

Primary losses

Harvesting

  • 20–25%
  • shattering if grain is too dry
  • unfilled and many green grains if too wet

Threshing

  • 20–25% for mechanical threshing
  • less than 20% for hand threshing
  • incomplete threshing, grain damage, and cracking/breakage

Drying

  • final moisture content is 14% or lower
  • spoilage, fungal damage, discoloration

Storage

  • less than 14% for grain storage
  • than 12% for seed storage 
  • less than 9% for long term seed preservation
  • fungal, insect, and rat damage 
  • loss of vigor 
  • loss of vigor

Milling

  • 13–14%
  • grain cracking and breakage
    overmilling