Quality Grain Storage Practices: Monitoring for Safety and Grain Quality Loss Prevention

From the January/February 2020 GRAIN JOURNAL.

By now, much of the 2019-20 crop is in storage. The wet weather certainly has presented challenges for harvesting and drying to safe storage moisture contents. This year’s challenges have been reflected in the increased number of grain handling and storage incidents. The number of reported entrapments and deaths in grain bins is much higher than in most years. Typically, the industry has lower numbers of disasters when the grain going into bins is lower in moisture content. Knowing that this year’s crop may present challenges, now is a good time to review monitoring protocols and schedules.

You can’t fix something if you don’t know it exists. And knowing about problems that exist inside of a grain bin is certainly a challenge due to the inherent poor access and visibility. It’s important to have a written monitoring schedule with plans on how that monitoring will be conducted. Methods for monitoring vary depending on economic investment. Any level of monitoring is better than no monitoring at all. The time and money involved with monitoring will support keeping workers safe as well.

It is well documented that most grain bin incidents happen with out-of-condition grain. Grain bridges, grain stuck to walls that breaks loose and causes an avalanche, big clumps that will not go through unloading sumps, and poor air quality all occur because of moldy, decomposing and insect-infested grain. Monitoring gives managers an opportunity to intervene before a catastrophe happens. It also provides a higher quality crop to sell. Better quality grain and reduced accidents both lead to higher profit.

When a thermocouple detects a hotspot, the monitoring system alerts the connected computer. Drawing courtesy Rolfes@Boone.

Monitoring Options

Low-technology options for monitoring grain include visual inspection of surfaces close to access points and odor detection (little training is needed for this). If the grain surface has a white or dark gray color, pulling a sample is a good idea. The off-color indicates mold or webbing from Indian meal moths on the top surface of the grain. Either condition will not improve on its own and can limit the ability of aeration systems to work properly. Moth webbing has a tarp-like effect and can also cause problems in the reclaim system. Removal of the webbing with a rake and fumigation may be necessary.

If odors are obvious when opening access doors, it’s important to find out why. Odors usually mean there is a leak in the bin or the grain is molding due to high moisture content at binning. The detective work to find the source can be challenging, but it is very important to locate the problem.

If the surface of the grain is easily reached without entering the bin, feeling the surface for higher temperatures can aid in identifying problems close to the surface of grain. If entering the bin is required, be sure to use the proper bin entry steps and personal protection equipment. Never enter without the proper equipment and always have a partner at the opening who is trained for emergency rescue and is in communication with the person entering the bin.

Several methods of monitoring using technology are available. Temperature cables are the most popular, and several studies show that cables have a very quick return on investment. While grain beyond about two feet from the thermocouples on the cables does not get monitored, temperature cables provide a good idea about microbial and insect activity in proximity to the sensors in the bin. Cables are like a communication system within the bin. Currently, these cables are the best and most economical way to determine what is going on inside the grain bulk. Without cables, a manager has no good indication of where problems exist on the interior of the stored grain, whether in a bin or in a ground pile.

There are several manufacturers offering cables with sensors that can display moisture content as well as temperature. (Editor’s note: for a list of suppliers, go to www.grainnet.com/gts.) These sensors measure the temperature and relative humidity around the sensor area in the cable. The cable system then calculates the moisture content from the equilibrium moisture content data programmed into the system for the type of grain in storage. This gives a good idea of moisture content close to the cables if the grain has been in storage long enough to equilibrate with the conditions in the bin. Some cable systems will send a message to cell phones and computers when a thermocouple reports rising temperatures (see Figure 1 above).

When looking at the display on the computer screen, any thermocouple node reporting a temperature above the temperature of the other nodes in the bin indicates grain at the point that has microbial or insect activity close to it (see Figure 2 on pg. 108). Increased aeration may temporarily reduce this temperature, but usually this is not a permanent remedy. Managers should consider moving the grain in the bin immediately to prevent further deterioration and problem areas growing in size. Left unattended, these hot spots can cause fires and explosions. At least, managers can plan on dealing with clods and ledges in the grain and damaged grain upon emptying the bin.

An increase in the CO2 level indicates some kind of microbial and/or insect activity in the bin. It does not indicate where the problem is located, but it can give a very early indication to the manager that a problem is forming.

Carbon Dioxide Monitoring

Another method for monitoring grain using technology is carbon dioxide (CO2) detection. All grain will have a low level of CO2 that is detected by monitors. Take a reading upon placing the grain in storage. This gives a baseline CO2 level for comparison. Then monitor the grain at the fan discharge upon fan startup every week.

An increase in the CO2 level indicates some kind of microbial and/or insect activity in the bin. It does not indicate where the problem is located, but it can give a very early indication to the manager that a problem is forming. CO2 monitoring is the best method to detect problems very early in their development.

Handheld CO2 monitors are inxpensive when compared to other monitoring methods using electronics. Having access to the discharge of the aeration fans can be a challenge unless the aeration system is a negative pressure system with the discharge from the fan at ground level. For positive pressure systems, a tube can be run from the headspace or vent outlets to ground level, providing ease in monitoring upon fan startup.

CO2 monitoring can be implemented after the grain is in the bin, while temperature cables must be installed when the bin is empty. If grain is already in place for this year, it is too late to institute a cable monitoring program. Put that in the plans for next year, and contact aeration and monitoring equipment dealers to start designing the best system for your operation.

A computer readout from a temperature cable monitoring system. Red and orange indicate problem areas.

Monitoring Frequency

Monitoring frequency is a common question for many storage managers. And there is no one perfect answer. A good rule of thumb is when the grain is above 40 degrees F, monitor weekly. Once grain temperatures drop below 40 degrees F, every two weeks is sufficient. Below 40 degrees F, insects and mold are much less likely to form and damage the grain. Above 65% relative humidity and about 60 degrees F, conditions are perfectly favorable for insect activity and mold development.

One strong advantage of electronic temperature monitoring and reporting systems is that they monitor grain continuously, around the clock and can report any changes in real time. This reduces labor dedicated to pulling temperature readings from cables by hand, recording them, and making comparisons to past readings to detect changes.

These systems also can reduce training and supervision of employees to make sure they are tending to temperature monitoring properly and on schedule. Most vendors report a two- to three-year return on investment for these electronic monitoring systems due to reduced labor costs and improved grain quality. Most of these electronic systems also are able to turn fans on and off at the proper times so that moisture content is not changed beyond limits set by the manager. These monitoring systems have nothing to do but monitor the conditions and make decisions about aeration operation. Employees have many other duties, so monitoring grain may not receive the attention needed to prevent grain loss and catastrophe.


Time and equipment to monitor are important every season, but seasons with wet conditions like 2019-20 make monitoring all the more critical. Establish your schedule, educate employees, and keep good records. This extra effort may mean the difference between having good grain quality to sell and having a fire or an employee death. Monitoring most certainly pays.

Reference: Oklahoma State University Fact Sheet BAE1290 Grain Handling Automation and Controls.

Dr. Carol Jones is professor of biosystems and agricultural engineering/stored products engineering at Oklahoma State University, Stillwater; 405-744-6667.