How to moisture test grain in a dryer

Why measure moisture accurately?

Grain drying is a critical step in harvesting. Grain that is too dry results in weight loss and therefore loss of income. Grain that is too wet, on the other hand, carries the risk of penalties, mold, or heating in the bin. The challenge intensifies when the grain leaves the dryer, as its moisture content is not uniform.

Depending on the type of dryer (batch, topdry, column, mix-flow, etc.), it is common to find moisture variations of up to 2%. Therefore, measuring a single sample almost always leads to misleading results. The real challenge is to establish a testing methodology that can:

• Minimize variance between tests

• Accurately represent the moisture content of the sample, and

• Provide reproducible data for decision-making

In this blog, we present a practical, documented testing protocol that you can apply directly to your next harvest.

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Understanding drying inconsistencies

Origins of moisture variations

When grain comes out of a dryer, the kernels are not uniform for multiple reasons.

• The flow of hot air is never perfectly distributed.

• The location of the grain in the dryer influences how it dries.

• Variations in airflow and temperature create variability.

• Grain size varies.

• Grain moisture varies.

CAUTION!

Moisture meters are not perfect! Although some commercial moisture meters are very accurate, moisture variance in your test or sample can be misleading. This is especially true for grains such as corn because variations in kernel shape and size can influence the moisture meter reading.

In practice

• Two samples taken 5 minutes apart may show a difference of 1.5 to 2.0 moisture points.

• A single rapid test is not sufficient to accurately determine the representative average.

Importance of variance

Variance is a key indicator: it measures the dispersion of results around the average. In the context of drying, it is inevitable, but must be reduced and controlled through a rigorous protocol.

Variance management

Repeatability vs. reproducibility

• Repeatability: same operator, same instrument, same sample

• Reproducibility: different instruments

A moisture meter with excellent reproducibility, such as the Perten AM5200-A, will allow you to measure the variance in your samples more clearly. You will also need to perform fewer tests to measure it.

Two moisture meters from the same brand will also have better reproducibility. This means less room for different readings between a buyer and a seller. Comparing two different meter models will always result in a difference. This difference will be even greater if you compare two moisture meters with different technologies, such as Perten's AM5200-A and the Labtronic 919.

Strategies for reducing variance

• Standardize your testing protocol.

• Train and educate operators on your protocol.

• Increase the number of subsamples.

• Systematically record all data.

Practical example

Measurement taken at the outlet of a continuous dryer:

• Test 1: 15.2% -> Minimum extreme value

• Test 2: 16.1% -> Maximum extreme value

• Test 3: 15.6%

•  → Average: 15.6 % ±0.45

The difference shows an acceptable variance (±0.45), if controlled. In fact, depending on your type of dryer, this variance may vary depending on:

• The type of grain

• The type of dryer

• The amount of moisture removed during drying

By taking systematic moisture measurements during drying, you will be able to determine the behavior of your dryer and better control your drying process. Taking a single moisture test can be misleading because that result may be on the extreme of the average. For example, if the single test result is on the low extreme of the average (Test #1: 15.2), you  underestimate the actual moisture content of your grain (average: 15.6%).

CAUTION:  

If your grain moisture is higher than you think, you are at greater risk of storage problems!

How can you control variance?

Simply by performing repeated tests. If you take a sample and test it again, you will see a difference, especially when it comes out of your dryer! If you calculate the average for your sample, after a few tests you will see that the average stabilizes. 

• When the variance is low, perform 3 tests to obtain a reliable value.

• When the variance is high, perform 5 to 8 tests to obtain a reliable value.

The basis of a reliable testing protocol

Three pillars

An effective protocol is based on:

1. A standardized testing method: minimizing the effect of the operator and the instrument

2. Representative sampling: the more collection points the sample includes, the more it reflects reality

3. Documented repeatability: a history of reliable and reproducible results, and the application of robust acceptance rules

   
   

Objectives

• Determine the actual average moisture content of the sample

• Identify extreme deviations; i.e. variance

• Obtain a figure that can be compared over time and between operators

The art of sampling grain

Sampling methods

• Continuous sampling: place a container under the dryer outlet for 30 to 60 seconds to obtain a representative flow.

• Multiple samples (bulk): manually take 8 to 10 small samples at regular intervals, then combine them.

Homogenization

A sample must be thoroughly mixed before use.

Required sample quantity

• Small grain (cereals): 9 liters (½ 18-liter bucket)

• Large grain (soybeans, corn, etc.): 13 liters (¾ 18-liter bucket)

Step-by-step protocol

Step 1 — Prepare

• Prepare bucket, divider, labeled bags, moisture meter, notebook

• On the sample bag label, note the current conditions (dryer temperature, flow rate, time).

Step 2 — Sample

• Batch drying

  • Take 8 to 10 subsamples.

• Continuous drying

  • Take a sample for 30 seconds (minimum).

• Mix the sample by thoroughly stirring it inside the bucket to ensure the sample is homogeneous.

Step 3 — Mesure moisture

• Maintain the representation of the sample when you reduce the quantity using a divider or buckets.

• Perform moisture tests (3 to 8 times depending on the variance obtained).

  • If the grain is very hot, temper the grain before testing (15–30 minutes).

  • Otherwise, test the grain immediately.

Step 4 — Document results

• Note:

  • The average

  • The extreme values (minimum and maximum)

  • The variance (standard deviation)

• Notes for continuous dryers:

  • If the moisture content at the dryer inlet varies significantly, repeat steps 2 to 4 every 15 minutes.

Common errors

• Not calibrating the moisture meter → bias with the market

• Taking a single sample → extreme value

• Forgetting to homogenize → reading error

• Testing a sample that is too hot → grain perspiration affecting the reading

• Approximing weight → reference error

  
  
  
  

Conclusion

Measuring moisture at the outlet of a dryer is not a trivial task; it is a strategic operation that directly influences preservation, compliance, and your income.

A single spot test is insufficient in a context of non-homogeneous drying, such as corn drying. Only a structured protocol, combining rigorous sampling, repeated measurements, and reliable testing equipment, can reduce variance and produce reliable results.

Producers and grain centers that apply this type of method gain not only accuracy, but above all confidence: confidence in their drying decisions, in the quality of their grain, and in the market value at the time of sale.