Here’s a tip for canola growers about dockage, conspicuous admixture and grades — pay attention to the sieves.
If your canola is downgraded due to conspicuous admixture, or if you feel your dockage is too high, check with the buyer about what sieves were used to determine dockage — material that isn’t canola and buyers don’t pay for.
When assessing dockage in canola, sieve selection is key.
In some cases farmers will earn more money selling a higher grade of canola, even if it results in more dockage, but to be sure they should do the math.
“You can potentially increase the dockage percentage on a sample of canola if that will help improve the grade and value of your product,” Usman Mohammad, a CGC inspection specialist said in an interview following a grain-grading workshop here Dec. 7, organized by the Manitoba Canola Growers and Manitoba Wheat and Barley Growers associations.
Under Canadian Grain Commission (CGC) regulations, when determining dockage, grain company and CGC inspectors alike are required to clean canola so the farmer gets the best possible grade and an accurate assessment of dockage, Mohammad said.
“Most years, most canola grades No. 1 and that’s what the CGC has found through its harvest sample program this year. But there might be rare cases where you won’t have a No. 1 because of too much conspicuous admixture remaining in the sample even after normal cleaning.
“There are a lot of considerations for grade improvement. The last thing you want is to not get a No. 1 because the cleaning sequence wasn’t done according to the CGC-approved method.”
The provision, found in the CGC’s Official Grain Grading Guide, is called “cleaning for grade improvement” and states the following: “If the grade of a delivery can be improved by additional cleaning, perform the cleaning and add the additional material to dockage. Cleaning for grade improvement can be done at any time after the cleaning assessment has been completed. After the cleaning assessment has been completed, examine the material to be removed and select your equipment according to the material you want to remove.”
The equipment consists of six CGC-approved round-hole sieves and five slotted sieves and the Carter dockage tester.
The CGC defines conspicuous admixture as “material that remains in the sample after cleaning and it is easily distinguished from canola without the use of magnification.”
Conspicuous admixture is removed by hand after the canola sample has been cleaned to determine the dockage. (Conspicuous admixture is included as dockage.)
The tolerances for conspicuous admixture in No. 1, 2 and 3 canola is 1.0, 1.5 and 2.0 per cent respectively. With such tight tolerances it’s important to use the right combination of sieves when determining dockage, Mohammad said.
The CGC says inspectors are to use the round-hole sieve that allows “reasonably sound canola” to pass through while removing large material.
The slotted sieve reduces the “admixture of conspicuous inseparable material within the grade tolerance with a minimum loss of reasonably sound canola.”
When selecting a round-hole sieve the goal is to separate larger material on the top while allowing the canola to fall through, Mohammad said. What’s on top of the round-hole sieve is part of the dockage. If a lot of canola doesn’t fall through the round-hole sieve it will also become dockage, reducing what the farmer is paid. To prevent that, the inspector can try a larger round-hole sieve, he said. However, that can increase the admixture.
The dockage captured on top of the round-hole sieve is kept in a bowl. What falls through will be mostly canola with smaller material such as weed seeds.
The sample — approximately 250 grams at a time — is then poured over a slotted sieve, which is moved from left to right 30 times using a sifting motion. The total distance from left to right is 20 cm or about eight inches. The fine material that falls through is also dockage and kept in a separate bowl.
Dockage is kept separately making it easier to try different-size sieves later if the canola is downgraded or if other adjustments need to be made.
Now the ‘screened’ canola is placed in a Carter dockage machine with settings prescribed by the CGC. The machine’s riddle removes any large material that’s left and it’s added to the dockage captured by the round-hole sieve.
Material removed via Carter machine aspiration is placed in a bowl and counted as dockage too.
Now the cleaned material is divided into portions of at least five grams and not more than 50.
From this portion the inspector hand picks the conspicuous admixture, such as cow cockle, lamb’s quarters, cleavers, smartweed, ball mustard and pigweed seed.
The admixture is weighed and the percentage calculated.
If admixture exceeds grade tolerances the inspector should consider using a larger slotted screen to reduce the admixture and improve the grade.
For example, say the admixture is 1.5 per cent, making the canola a No. 2. The inspector might have used a .028 slotted sieve, which is the smallest option. Using the largest slotted sieve — .040 — will allow a lot of material to fall through, reducing the admixture.
Say the admixture drops to 0.2 per cent, now the grade goes to a No. 1, but dockage has increased. By using a .035 slotted screen the admixture might increase to 0.8 per cent. That’s still under one per cent so the grade remains No. 1 and there’s slightly less dockage.
“That’s an example of what an inspector needs to think about when assessing dockage on canola,” Mohammad said. “The point I am making is when you go straight to the .040 slotted sieve from the .028 there are other sieves in between you can use (.032, .035 and .038),” Mohammad said. “If you select the .040 slotted right away you’ve really reduced your conspicuous admixture percentage well below the tolerance to improve your grade to a No. 1 but your dockage may be higher than what it actually should be.”
You might have some space to make further adjustments. For example, you can use a .035 slotted sieve instead to reduce the admixture while achieving the same grade improvement and lowering the dockage percentage to help out the producer, he said.
For more information on determining dockage go to the CGC’s Official Grain Grading Guide or contact the CGC.