Measuring Grain Moisture Levels

Accurate moisture tests are important in
managing and marketing grain. Inaccurate
tests can lead to:
• Spoilage
• Moisture shrinkage and drying charges
• Extra drying costs and loss of value
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measuring grain moisture levels
Grain Moisture
Why measure grain moisture?

Accurate moisture tests are important in managing and marketing grain. Inaccurate tests can lead to:

  • Spoilage if grain is too wet and is placed in low temperature (air heated less than 10 degrees F) or natural-air drying bins
  • Extra drying costs and combine losses if grain is harvested wetter than necessary
  • Moisture shrinkage and drying charges when grain is sold too wet
  • Extra drying costs and loss of value when grain is dried below the market standard
Obtaining a Representative Grain Sample

Obtaining a representative grain sample before harvest is difficult. For combine-harvested grain, it is probably best to harvest a small area, then sample the shelled grain. If this isn't practical, hand pick and shell grain from several plants and mix together. Make three moisture tests on this sample and average the results.

When sampling a loaded vehicle of any grain, probe the load in at least two locations (avoid center and corners); or better yet, sample the flowing grain during unloading. To sample flowing grain, pass an open container completely across the grain stream every 50 bushels or so, and pour the collected grain into a bucket. Mix the grain in the bucket and draw out the amount needed for a moisture test. Be sure the grain is thoroughly mixed. Scooping a can full off of the top is not adequate.

When checking moisture of binned grain, use a six foot or 10 foot probe to collect samples from various depths. Go as deep as possible at bin center and several other locations. Do not mix the samples. Knowing moisture content at different locations can help you find the drying front in drying bins or trouble spots in storage bins. If you don't have a probe, take the samples at arm's length below the surface.

Warning: Be extremely careful when entering bins. Crusted grain can cave in unexpectedly. Never enter a bin that is being filled or emptied. Wear a dust-mist respirator, especially if any spoilage is evident. If there is an oxygen-deficient atmosphere, avoid entering the bin or use a Supplied-Air System.
Using your Grain Moisture Tester

If you are using a portable grain moisture tester, first make sure the battery is charged. A low battery can cause inaccurate readings. The battery should be removed during the tester's long, idle periods to prevent damage from leakage, and replaced at least once per year.

Be sure that you read and understand the manufacturer's instructions. Pay particular attention to the tester's temperature compensation method. Grain temperature can have a large effect on moisture readings. Some testers have automatic temperature compensation, some compensate only after you push a button, and others require that you measure grain temperature, then add or subtract a correction factor to the moisture reading.

Cold grain temperatures will usually cause low readings, unless moisture has condensed on the surface. With condensed surface moisture, electronic testers will usually give high readings. Moisture condensation occurs when cold grain is removed from storage on a warm, humid day, or when cold samples are taken into a warm, humid room. Cold grain should be warmed in a sealed container before making moisture tests.

Testing hot grain from a dryer is difficult, too. Electronic testers tend to understate the moisture content of hot or rapidly cooled grain. Grain also loses moisture as it cools. To get the actual moisture content of hot grain, let it cool slowly in a sealed container before testing.

Remember, all grain moisture testers show some variability. Different readings can be obtained when the same sample is tested repeatedly. Because of this, you should test each sample at least three times and average the results.
Checking your Grain Moisture Tester's Accuracy

Checking your moisture tester's readings against readings from your mill or elevator's tester is a good idea. Most of these grain moisture testers are checked by your state Department of Agriculture or sent back to the manufacturer annually for inspection and calibration. You should do this once per year.

To do your own check, test each grain sample three times in your tester and calculate the average reading. Repeat this process with the elevator/mill tester. If the difference between the average readings is greater than 1.0 point for dry grain or 1.5 points for wet grain, you should have your tester serviced.
Do's and Don'ts of Grain Moisture Testers

Do Don't
Obtain a representative sample. Ever enter a bin that is being filled or emptied.
Replace tester batteries once per year. Use your grain moisture tester without reading instructions.
Check your grain moisture tester's accuracy once per year. Test grain that is too cold or too hot.
Grain Moisture Testers Grain Moisture Comparison Chart