The facilities manager of the world’s biggest canola crushing facility says a lot happens to the black seed after it is dropped off in the driveway.
Scott Johnson, manager of Cargill’s operation in Clavet, Sask., told delegates attending the 2016 Sask-atchewan canoLab workshop that the facility’s two plants crush the equivalent of 5,500 acres of canola a day.
The first step in the process is removing rocks and coarse dockage from the shipment.
Moisture and temperature are the two keys to the crushing process. Cargill needs the seed to be at six percent moisture content and 80 C to begin the process.
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Flaking is the first stop in the journey through the plant, where the heated canola makes its way through two big steel rollers moving in opposite directions.
“The seed goes between them and then we just smoosh that seed up,” said Johnson. “It’s a very precise operation. We’re targeting about 12 thousands of an inch thickness.”
The canola then enters the cooking process, where it is taken down to three percent moisture content and heated to 100 C. From there it moves to the expeller, where two-thirds of the oil is removed from the seed.
“We’ve got a screw that goes inside what we call a cage, and we basically squeeze those flakes,” he said.
The oil pours through the holes in the cage and the meal goes out the other end of the processing line.
The expelled oil contains 10 percent fines that need to be removed. That is done by dragging a coarse steel chain along the bottom of the tank and then spinning out the remaining fines in a horizontal centrifuge.
The press cake left over from the expeller process still contains 16 to 18 percent oil.
“We want to get all of that oil out,” said Johnson.
Hexane is used in a solvent ex-traction process to absorb the oil contained in the press cake. The hexane is boiled to separate the oil and then condensed and reused thousands of times.
Oil from the hexane process is mixed with the oil from the expeller process and stored in a crude oil tank.
The white meal that remains contains less than one percent oil but about 30 percent hexane. It is heated up to get rid of the hexane and then cooled.
That meal contains 35 to 36 percent protein, which is much lower than soybean meal but suitable for dairy cattle rations.
One of Cargill’s plants in Clavet is generally used for commodity canola and the other for specialty canola. The facility also has a refinery, where oil from the two plants is refined into a food grade product.
“We just need to clean it up and get rid of the impurities,” said Johnson.
The first step in that process is degumming, where the phospholipids are removed from the oil. Canola oil typically contains 500 parts per million phospholipids.
Water is added to the oil to hy-drate the phospholipids. The mixture is then placed in a centrifuge, where the heavy phospholipids go to the outside of the mixture and are separated from the oil.
Bleaching is the most misunderstood step in the refining process.
“We don’t add bleach to the oil, but we are removing colour.”
Canola contains chlorophyll and other components that make the oil green or dark red in colour, which is undesirable for the North American market.
Bleaching clay, which is a naturally mined mineral, is added to the oil.
“It is very fine. It’s like talcum powder,” said Johnson.
The unwanted colours stick to the outside of the clay, which is then filtered out. Unfortunately, the clay also absorbs some of the oil.
The industry wants the Canadian Food Inspection Agency to allow crushers to put the used bleaching clay back in the meal because 25 percent of its weight is oil, which would be a valuable ingredient in the meal. Crushers in the United States are allowed to do that.
“Today in Canada we can add clay to our meal and we can add oil to our meal, but we can’t add spent clay to our meal,” he said.
Deodorization is the final step in the refining process, which takes out anything that can affect the taste of the oil. Food grade oil should taste like nothing at all when you swirl it in your mouth.
The oil is heated to 260 C to strip off any undesirable flavours.
“We also operate this thing at almost a full vacuum, so pretty extreme conditions,” said Johnson.
The end result of the crushing and refining process is 43 percent food grade oil and 57 percent meal, which is destined for the California dairy market.
