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Keep Better Track of Stored Grain Temperature

Keep Better Track of Stored Grain Temperature

Many on-farm bins need a better system to help keep track of stored grain temperature to maintain grain quality; many bins also need a fan in the top to properly ventilate the peak area to prevent moisture condensation.

Charles Hurburgh, a professor of agricultural and biosystems engineering at Iowa State University, is director of the Iowa Grain Quality Initiative. What feature would he most like to see in on-farm grain storage systems? What are the two key improvements farmers should consider making to their bins?

First, he'd like to see bins especially the larger bins being built on farms today have a good system for monitoring stored grain temperature. There are such systems available and he thinks that would be a very worthwhile investment for farmers to make. The second thing he sees lacking in many bins is the need to properly ventilate bin peaks; the area at the top of the bin between the surface of the grain and the roof of the bin.

For storage bins (not drying bins or dryers) he observes that many on-farm grain bins need a system to keep track of grain temperature. It's hard to track grain temperature and maintain grain quality in large structures.

There are several types of grain temperature monitoring systems on the market. Hurburgh says a system that records the temperature data over a period of time is most useful. Increases in temperature of stored grain indicate the grain is heating up, alerting you to take prompt action. You'll either have to remove the grain or run some air through it with fans to prevent spoilage.

In large bins, manually probing doesn't give a good reading

"In the larger bins there's no practical way to manually take the temperature of the grain and get a representative reading," says Hurburgh. "Take a normal thermometer, shove it in the grain and you have a temperature at that point. But grain is a pretty good insulator, so only 10 or 15 feet away, the grain temperature could be quite different."

Furthermore, large bins are a long climb up the ladder to enter them and probe the grain, so this may not happen frequently. Grain needs to be checked on a regular schedule during storage.

The most common monitoring systems being used today drop a wire into the grain at several places, with thermocouples every 10 feet or so and you get a read-out on each cable. If there's 50 feet of grain, there may be five or six thermocouples reading the temperature and you have four or five of the cables in the bin. So you get 25 or 30 places where temperature is measured in the grain.

That increases the odds of finding something going wrong in the bin, such as a hot spot developing in the grain mass. It doesn't always mean the cable will go through the hottest grain, but if you get a spot where temperature is starting to rise you know somewhere in the area near that thermocouple, there's a problem.

Ventilate bin peaks properly—another need of many bins

The second thing Hurburgh encourages farmers to consider is to make sure they have adequate ventilation in the peak area of bins. The ventilation should be enough to clear the condensation that gathers under the roof if you try to store cold corn into the spring and summer.

"We try to keep grain cold through winter," notes Hurburgh. "That's great for the grain to help maintain quality because it discourages mold formation." He says there's no problem with freezing grain in Iowa. In fact, in the fall of 2009, when corn was coming out of the field late and wet, Hurburgh recommended freezing the corn. About all you could do was take a chance and freeze the grain to avoid mold formation and corn deterioration during storage.

The problem is, when grain is that cold, and you get a warm day in late winter or if the weather starts to warm up in early spring, the potential for condensation of water on the underside of the roof gets to be pretty high, he explains. That water drips back down onto the grain.

Peak ventilation can fix the moisture condensation problem

To fix this water condensation problem, you select times when the weather is warm outside and the grain is cold in the bin, and move air in under the bin roof and then out the exhaust vents. Thus, the ventilation doesn't allow the build up of moisture to create condensation under the roof.

Can you do that just by having enough vents in the roof area or do you need a fan up there in the peak? Hurburgh says vents will work fine at the time the fan at the bottom of the bin is running, as long as there are enough vents that pushing air up through the grain doesn't add to the static pressure. However, the vents will do very little when the fan at the bottom of the bin is not running; for example, if the fan is capped off and closed.

"If the grain is cold and the weather is warm outside, I don't want my bottom fan running anyway because I don't want to change the temperature of the grain during the winter," adds Hurburgh. "I know the outside air temperature is going to go back down as the weather gets cold again. That's why you need to have ventilation in the roof peak."

It's better to have a fan up there to ventilate that area and exhaust the moisture out through the vents rather than let it condense on the underside of the roof. Bin companies have the recommended horsepower you need for these fans, based on the volume of the peak area. "It's important to follow those recommendations for properly sizing these fans," notes Hurburgh.

For more information on stored grain management, go to the Iowa Grain Quality Initiative website at

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