Canola can be harvested dry and relatively cool but once it’s in the bin, microbial activity continues and creates moisture
Canola can be tough crop to store.
“Just because it’s in the bin doesn’t mean you can stop managing it,” said Joy Agnew, who researches canola storage for PAMI.
The key to storing canola is to constantly monitor its temperature and condition and understand what the crop needs to stay sound in the bin.
Canola is considered dry at 10 percent moisture content, but lower moisture content is recommended to help reduce spoilage. Most producers are targeting eight to nine percent moisture content before the crop goes in the bin.
High temperature grain can also cause spoilage. It is often a combination of the two factors that cause the problem.
Even dry canola needs to be kept below 15 C to be safe.
Temperature and moisture content can be managed by blowing air through the grain, but Agnew said there are misconceptions about this practice.
One is that aeration is the same thing as natural air drying. Agnew said they are two different things.
Aeration cools or conditions the grain, typically by using a low airflow rate of .1 to .2 cubic feet per minute per bushel.
“The physics behind cooling or conditioning of the grain is straight forward,” she said.
“If the outside air is cooler than the grain and you blow that air through the grain, then the grain is going to cool.”
Agnew said operating continuously for eight days at .1 cubic feet per minute per bushel is a good rule of thumb when calculating the length of time needed to run the fans to achieve cool air conditioning and equalize the temperature of the grain in the bin.
Natural air drying doesn’t just equalize temperature but also removes moisture from the grain.
The airflow rates to achieve natural air drying are 10 times higher than for aeration.
“You are targeting one to two cubic feet per minute per bushel to actually remove moisture from the grain,” she said.
The air is able to dry when the air equilibrium moisture content is close to the target grain moisture content.
Unlike aeration, there is no easy rule of thumb to follow when determining how long to run the fans because it depends on outside conditions such as temperature and relative humidity.
“The general recommendation for both aeration and drying is turn the fans on and let them run continuously until you’re satisfied with the temperature or moisture content,” Agnew said.
Fan control systems and strategies are available that may help producers run their fans and in-crease efficiency for aeration and natural air drying. For example, producers may not want to run their fans when high moisture content is in the air.
Weather Innovations Consulting provides a forecast for equilibrium moisture content in the air called BINcast.
The online model provides five-day, site-specific forecasts of optimal times for operating fans by predicting equilibrium moisture content.
Canola seeds are small, so the space between the seeds is tight when packed together in the bin.
This makes it difficult to achieve a high airflow rate through the grain, and larger fans are required to dry canola than what is necessary for crops such as wheat.
Canola seeds are still alive for up to six weeks after harvest.
“So canola can be harvested dry and relatively cool, put in the bin and you think it’s safe and three weeks later it’s heating because there is still microbial activity going on generating its own moisture,” she said.
Green seed often enters the bin the way it comes off a field, in localized pockets. These can result in hot spots in the bin that promote spoilage.
All canola should ideally go into an aeration bin so that producers can blow air through the crop and control hot spots.
“Canola with dockage or green seeds must go into an aeration bin, because that is really the only way to control hot spots,” Agnew said.
“Canola with dockage and green seeds can almost be guaranteed to form hot spots sometime during storage.”
Producers who don’t have access to aeration bins must check on their canola often and be ready to turn the grain to even out the moisture. Long-term storage requires that temperatures below 15 C are maintained well into the following season.
Producers can cool their canola by running fans in the winter, but care needs to be taken because any cooling action in the bin is going to dry the grain.
The cooling should be done in stages rather than leaving the fans on and cooling the grain all at once.
“Target about a 10 C drop each time the temperature changes so that you can cool a little bit further,” she said.
Agnew’s research has shown that the grain should be left alone once it is cool.
“Don’t turn it, don’t aerate it, just leave it,” she said.
“This was a direct result from our study last summer where we had a bin that was turned, a bin that was aerated and a bin that was left alone. They all started off at about – 20 C, and the bin that was left alone was the most stable throughout the entire year.”
Bin sensing technology is useful, but producers should be careful how much they trust their bin sensors because they will give only the average temperature in the bin and won’t pick up hot spots.
Canola has high insulating cap-acity, and a sensor may not pick up a hot spot even if they are close to each other.
“A sensor is monitoring about a bushel or two around it. Until that hot spot grows and affects that one or two bu. around the sensor, you have no idea, ” Agnew said.
“Cables for monitoring temperature are great, you just have to understand the limitations. In a 2,500 bushel bin with four sensors, it represents about two percent of grain in that bin.”
Producers who want to watch for hot spots should track the temperature trend over several hours or days rather than just looking at the absolute temperature value one or two times a week. A slight increase over a couple days may indicate a hot spot that is near one of the sensors.
For more information, visit www.pami.ca