The evolution of rapid moisture testing at the Canadian Grain Commission

Moisture content in grain

The moisture content of grain affects its quality, safety and storage life. High moisture levels encourage the growth of insects, fungi and bacteria and affect physiological processes, such as sprouting. The most accurate method for determining the amount of moisture in a sample of grain is to dry it in an air oven and measure the change in mass. For many years, however, the grain sector has used moisture meters to rapidly predict moisture levels in grain. These meters are based on the principle that the electrical conductivity of grain increases as moisture increases but to give accurate results, they must be calibrated using the air oven reference method. Our lab is responsible for monitoring and maintaining the calibrations for the commonly used moisture meters in Canada.

Early advances in moisture testing technology

The methods used for rapid moisture testing at the Canadian Grain Commission have changed with innovations in technology. The Board of Grain Commissioners for Canada (the precursor to the Canadian Grain Commission) first began evaluating moisture meters in 1934 and found that the motor operated Tag-Heppenstall meter, which measured the electrical resistance of a current passing through grain, was the most accurate for wheat and barley at that time.

Advances in electronics led to the availability of moisture meters that measured the electrical capacitance of grain samples at a frequency of 18 MHz. By 1959, the Canadian Grain Commission was using this technology in 919/3” moisture meters and in the early 1980’s changed to 919/3.5” meters which could accommodate larger seeds. In the late 1990’s, the Canadian Grain Commission began evaluating moisture meters that used the same technology as 919/3.5” meters but offered a higher degree of automation. In 2005, Seedburo Model 1200A became the official moisture meter at the Canadian Grain Commission.

Introduction of the Unified Grain Moisture Algorithm

In 2007 a new method for measuring moisture content, the Unified Grain Moisture Algorithm (UGMA), was developed and made available for use in moisture meters. This method uses a measurement frequency of 149 MHz, which was found to reduce the influence of grain parameters such as weight, grain type, seed size or shape and growing conditions. As a result, the accuracy and stability of the calibrations for all grain types were improved over a wider temperature range and separate grain calibrations were not needed for lightweight samples. The Canadian Grain Commission began evaluating UGMA meters in 2012 and found that their moisture predictions were equal to or better than those from 919 meters. In 2015, after using 919 meters for more than 55 years, the Canadian Grain Commission began using UGMA meters for official moisture testing.

Calibration of moisture meters

We monitor and maintain calibrations for UGMA moisture meters and the conversion table for 919/3.5” meters on an annual basis for all regulated grains depending on sample availability. Our monitoring process evaluates the differences between results from the air oven reference method and the moisture meters. Changes to calibrations are made when we find a consistent difference, outside the range of assigned tolerance, with the air oven results for at least 3 years and sufficient samples have been tested across the full moisture range. Calibration changes to UGMA moisture meters are made in conjunction with the manufacturers and calibration updates are released annually. The 919/3.5” conversion tables are available on our website. Even though both types of moisture meters are calibrated against our reference air oven method, they can give slightly different results due to factors such as grain density, sample weight and operating temperatures.

We may use UGMA technology for the next 50 years or technology may advance again. The Canadian Grain Commission will, however, continue to evaluate improvements in moisture meter technology as they develop.