Where aeration or natural air-drying can't get your canola to the condition you need, heated-air drying may be the answer, but the crop's properties will require you to take steps to protect it.

Hot-air drying differs from natural-air drying in that heated air will absorb much more moisture from the grain -- and warming of canola forces moisture out much more rapidly, according to the Canola Council of Canada.

Drying decisions will depend on how much time you have for drying before mould starts to grow. Canola dries at a lower rate than cereal crops do, as canola crops are smaller, more densely packed seed, which translates to reduced airflow through the crop.

And because canola offers more resistance to airflow than cereal grains, the fan on a dryer operating at the same speed used for grains will produce a higher static pressure but much less airflow. This means the temperature of the hot-air plenum will rise, unless you reduce the fuel flow.

Keep in mind also that most grain dryers are designed to handle wheat and corn and need to be adjusted and checked to make sure canola's not leaking out or being blown from the drying chamber by higher static pressure.

Screens and floors of dryers more than 10 years old should be checked for rust holes, to prevent canola leakage. Green weed seeds and canola stems and pods can interfere with canola passing safely through a dryer, and at high drying temperatures, stationary canola may catch fire.

Canola seeds can also ignite when they go by the burner. You can reduce your fire risk by cleaning the seed to remove light or fine material.

Before you dry canola, you'll want to remove any debris built up on the walls and other areas of the dryer, use wind deflectors to prevent airborne material from being pulled through the burner -- and avoid overdrying the seed.

The maximum air plenum temperature for drying canola depends on your crop's seed moisture level, seed viability temperature, expected storage period, type of dryer used and other factors.

Overdrying canola causes seed coats to crack, and damaged seeds show a marked rise in the level of free fatty acids, meaning lost oil quality. Seeds dried to moisture levels below six per cent are very fragile and subject to mechanical damage during handling, whereas seed above seven per cent moisture won't suffer cracking. That said, visible cracks and blackening have been observed on seeds dried at an "extreme" temperature of 250°C, the Canola Council noted.

Canola destined for use as seed should be dried at less than 45°C, but if it's headed for crushing and oil extraction, canola seeds can be dried at up to 82°C. Lower temperatures should be used when canola is damp (over 12.5 per cent moisture) or when it's to be stored for over six months.

Canola considered "tough," at 10 per cent moisture, can be exposed to drying air no warmer than 49°C if it's to be used for seed. Tough commercial canola can be dried at maximum drying air temperatures of 82°C, for canola that's mixed during drying, but no warmer than 71°C if unmixed.

Canola considered "damp" (12.5 per cent moisture) should be exposed to drying air no warmer than 43°C. Damp commercial canola can be dried at a maximum drying air temperature of 71°C if mixed during drying, but no warmer than 60°C if unmixed.

Generally, wetter seed requires a longer drying process at a lower drying temperature. Seed viability is adversely affected when drying temperature is too high; damage is more likely to occur when the seeds are dry or nearly dry.

To prevent seed damage, it's important that maximum seed temperature does not exceed the maximum allowable temperature for the type of seed and its intended purpose.

A non-recirculating batch dryer or a dryer that doesn't mix or circulate the seed requires a lower operating temperature, because seeds next to the hot-air plenum will warm to near the hot-air temperature. That's why, for such dryers, temperatures 5° to 10°C lower than those listed for commercial use are advised.

-- Adapted from the Canola Growers Manual, published by the Canola Council of Canada.