To dry or condition, that is the question

October is a busy month for Joy Agnew.

As the grain storage expert with PAMI, an agricultural research and innovation institute based in Humboldt, Sask., Agnew receives dozens of phone calls and emails from farmers who have technical questions about grain drying and grain conditioning

Agnew spoke to The Western Producer in mid-October about grain conditioning

WP: Do most farmers understand the difference between grain conditioning and grain drying?

Agnew: No…. The confusion is the misunderstanding that aeration is the same as drying. It’s not.

WP: What is the difference?

Agnew: Aeration is what (causes) conditioning, or making the temperature distribution in the bin uniform. Drying actually removes moisture from the grain. The fundamental difference between the two is the airflow rate. The more air you put through the grain, the more likely you are to achieve drying….

So .1 cubic feet per minute (of air flow) will result in aeration or conditioning, (but) 1.0 c.f.m. per bushel is required for drying.

WP: Are natural air drying and aeration two different things?

Agnew: Yes. natural air drying is the higher airflow rate, resulting in moisture removal. Aeration is just conditioning.

WP: What should farmers do first, condition the grain or dry the grain?

Agnew: That’s kind of the ongoing debate right now…. Aerating when the outside temperature is cooler than the grain, say 5 or 10 C, that will help get the grain in a safe store condition no matter what moisture content is. Even if it’s a little bit tough, if you can cool it, it will be relatively safe to store.

The problem with that is as soon as the grain mass becomes cool, it becomes very difficult to dry. Ideally, remove moisture first and then (aerate) to get it both dry and cool.

WP: Why is it important to even out the temperature in the bin?

Agnew: If you have a temperature variation within the bin, you will also have a moisture variation within the bin…. If you have an area of higher temperature, that area can hold more water…. If you have temperature gradients, of differences, you’re going to have convection…. As the air moves around and changes temperature, it (the grain) could be gaining or dropping moisture.

WP: How is grain different from other stored materials?

Agnew: The grain is technically still alive. There is microbial activity happening within the grain that is generating it’s own heat and moisture. You also will have temperature gradients due to the grain mass itself. A good chunk of the grain is near the edge of the bin …. and a good chunk of the grain at the core of the bin, insulated by the rest of the grain.

WP: How long does it take to condition stored grain?

Agnew: There are all kinds of rules of thumb that you need something like 12 hours of fan operation to even out the temperature distribution.

WP: Why is it necessary to condition dry grain, or monitor grain bins throughout the winter?

Agnew: The grain is still alive, especially in the cases of canola and some of the pulses. The kernels are still respiring and producing their own moisture and heat. You could put it in the bin cool and dry, but that microbial activity has its own agenda.

WP: Why is PAMI studying storage of straight cut canola seeds? How is it different from canola harvested from a swath?

Agnew: It all comes down to variability of seed maturity. Swathed canola, you kill the plant and theoretically speed up the maturity of the seeds. The seeds are likely to be more uniformly mature when you combine. If you’re straight cutting … you could have more green spots…. That’s going to (influence) the prevalence of hot spots in the bin. Green seeds have higher moisture content and they’re more likely to heat or have the microbial respiration that causes heat and moisture.

WP: On PAMI’s website at, there are charts on the equilibrium moisture content of air, which can be used to predict how ambient (outside) air will affect the moisture content of grain. Should these charts be posted in a machine shop or next to a grain bin?

Agnew: Definitely…. There are also some really cool tools coming out online and available for apps. There’s one … that is basically a five-day equilibrium moisture content forecast. Rather than having the chart there and deciding based on the current conditions, you can plug in your location to this app, plug in the grain type … and it gives you equilibrium moisture content forecast for the next five days. You can decide whether the next five days look reasonable to turn on your fans or not.

WP: Despite all the available information, it seems like there is a high level of confusion around conditioning grain. Is there a good rule of thumb for producers who don’t want to sift through all the technical data?

Agnew: The generic rule of thumb is put air on it, especially (crops) like canola. It should be aerated no matter what.


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