Moisture in or moisture out?

Are you really drying that grain when you turn on the fans?

It’s the disaster no one wants to admit — a bin of spoiled grain can represent the loss of a producer’s entire year of profits.

When grain spoils due to problems with storage, “farmers usually sell it, burn it or hush it up,” says Joy Agnew, project manager for Agricultural Research Services at the Prairie Agricultural Machinery Institute (PAMI).

And it does happen. “As recently as last spring we got a call from a terminal that had 100,000 bushels of canola spoil on them,” she says. “They had sensors in the grain, but they weren’t working.”

Related Articles

The reasons for grain spoilage are complex, but they add up to the risk that hot or wet grain will spoil — fast. Until recently, the standard advice had been to keep the grain cool through continuous aeration, but researchers now say that might be inefficient, or even push moisture back into stored grain.

Agnew says most information out there about grain storage was developed during research trials in the 1980s and 1990s, when the average bin size was 2,500 bushels, compared with today’s 20,000-bushel-plus bins.

“We really don’t know how quantity and mass in the bin affect management,” she says. “For example, large bins have multiple ports for inputting grain. That could affect airflow and conditioning of the grain itself. Another issue: you can’t fill a bin from a single field — you’re pulling grain from different fields with different conditions. They will layer in the bin and affect airflow rate and conditioning.”

PAMI’s current trial on bin management looks at summer storage of canola in co-operation with several partner producers. “We want to monitor different practices — leaving it alone, aerating it and turning it,” says Agnew.

Producers generally put grain in bins, aerate it and leave it without monitoring it. But Agnew says continuous aeration can be inefficient. “The air’s capacity to dry depends on temperature and relative humidity,” she says. “So running the fans continuously means that a lot of the time when the fans are running, you’re not achieving anything because the air conditions are not conducive to drying.”

Heating is good for compost, but not grain.

Heating is good for compost, but not grain.
photo: Cereal Research Centre

Water in, water out

Ron Palmer, a researcher with Indian Head Agricultural Research Foundation, has been evaluating different methods of bin storage since 2010.

His claims that continuous aeration may not be effective generated some controversy last year at the CropConnect conference in Manitoba. But Palmer says his advice — to turn fans on at select times when the moisture content of the air is lower than that of the bin — is based on data.

Back in 2010, Palmer’s team found a way to calculate the amount of water in the air going into and out of the bin.

“We plotted these graphs out and I couldn’t believe my eyes: with the fan turned on continuously, it would be drying and drying and then it would be wetting the grain, then drying again. There was a distinct daily cycle of drying and wetting. The drying wasn’t taking place when we expected — it was taking place at night,” he says.

The team also found that whenever the grain was cooling, it was also drying.

“If the grain is cooled by 15 degrees you’re taking out one per cent moisture — that’s a nice rule of thumb,” Palmer says.

More recently, Palmer has been studying the dynamics of what’s going on in the bin when the air outside comes into contact with the grain.

“It turns out that if you take the absolute humidity (the actual amount of water in the air, as opposed to the relative humidity) of the air outside and it’s less than the absolute humidity of the air in the bin and you run your fans, you’ll have drying,” he says.

Keep it cold

Palmer emphasizes that there’s more than one objective when it comes to storing grain.

“We’ve always thought the only thing to worry about is getting the grain dry, but there’s a more important one than that: keeping it safe, protecting it from spoilage,” he says.

“In actual fact your grain starts to spoil the minute you take it off the combine. Grain has never gotten any better sitting in the bin — the only thing we can do is to stop that process. We can only do that by keeping it cold.”

He says producers should look out for two factors: moisture content and temperature.

“There isn’t a one-size-fits-all management practice. What is your objective? If it’s keeping the grain safe, you want to keep it cold,” Palmer says. The best management practice is to keep conditions controlled, where the fan only goes on when the outside air is less than the grain temperature.

The ‘yard light rule’

“If you want the most drying possible,” Palmer says, “measure the absolute humidity in the bin, measure the absolute humidity of the outside air, and if the bin’s AH is higher than the air’s, turn the fan on. And you get drying.”

As soon as grain comes off the field, producers should turn the aeration fans on immediately to cool the grain down.

When there are conditions for condensation, particularly in the spring and fall, they should leave aeration fans off to protect grain from the outside air.

Producers who lack sophisticated monitoring equipment should follow Palmer’s “yard light rule” — turn fans on at night and off during the day.

Agnew says monitoring is essential when it comes to grain storage — particularly when producers are storing grain in large bins and there’s more to lose.

But monitoring technology has a way to go. PAMI is working with University of Sask­atchewan mechanical engineering students to develop more effective sensors for large bins.

“I understand producers don’t have time to continually monitor, but they need to keep an eye on it,” she says. “A bin can go quickly.”

BINCast aeration forecasting

Website uses weather data to tell you when to turn the fans on and off

BINCast, the web-based aeration forecasting tool from Weather INnovations Consulting (WIN), is now available for use anywhere in the Prairies, Ontario and Quebec, says WIN president and business manager Ian Nichols.

The tool helps producers calculate when to turn the aeration fans on based on the moisture content in the air. In other words, it tells you whether turning fans on will add or subtract moisture from stored grains. Better yet, its range is five days, meaning producers have lots of time to plan aeration strategies based on projected conditions.

“Every grain has a propensity to exchange moisture with the environment, the atmosphere around it. It’s like osmosis. If the air is wetter than the grain, the grain will gradually take on some additional moisture. BINCast tells you what the equilibrium moisture content (EMC) of grain will be hour by hour if you run the fan right now,” says Nichols.

“BINCast helps you know whether your air quality is going to be good or bad, and good — if you’re trying to dry the grain — is an EMC below what your grain is currently at. You don’t have to measure the relative humidity of your bin and look up charts. This gives you a look into the future and lets you know how to plan for the next few hours.”

BINCast is available on the Manitoba Co-operator website at

About the author


Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

Julienne Isaacs's recent articles



Stories from our other publications