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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?

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.

Read: Moisture content formula and calculations
Read: Primary versus secondary method of measuring MC

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

in Harvesting

Higher moisture content results in more losses from poor grain quality; while, lower moisture content results in more losses from shattering.

For measuring moisture content during harvesting, the most practical option is to use a resistance-type moisture meter that gives quick results and only uses small samples.

The capacitive moisture meters are more expensive, require a larger sample, but are more accurate than resistance type units.

in Drying

Grains need to be dried to below 14%, and seeds should be dried to below 12%.

postharvest-16-moisture-content

Paddy should be dried to safe moisture content within 24 hours after harvesting to avoid damage and deterioration. Improper drying and storage practices lead to low grain or seed quality.

Read: What are the problems related to incomplete or untimely drying or storage of paddy?

Table: Comparison of methods used in measuring moisture content for drying

in Storage

Grains should be dried to a certain moisture content (MC) depending on storage period to avoid potential problems:

Storage period	Required MC for safe storage	Potential problems
weeks to a few months	14% or less	molds, discoloration, respiration loss insect damage, moisture adsorption
8–12 months	13% or less	insect damage
storage of farmer's seeds	12% or less	loss of germination
<1 year	9% or less	loss of germination

A rule of thumb for seed is that the life of the seed will be halved for every 1% increase in moisture content or a 5°C increase in storage temperature.

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