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Canola seeds can lock in green when frost or high temperatures stop or interrupt the chlorophyll-clearing process. No.1 canola cannot have more than two per cent green seeds. Green seed can also increase storage risk, even if canola is dry and cool.
This article has the following four sections:
Grading factors for green seed
Processors don’t want chlorophyll in canola seeds. It can give the oil a green tint. Processors use a clay filtration process to remove chlorophyll, and canola oil with more chlorophyll will require more clay and possibly more passes with the clay to remove it. This adds to processing cost. Clay filtration also removes some oil, reducing the overall oil yield from a tonne of canola seed.
The Canadian Grain Commission’s Official Grain Grading Guide says:
- No.1 canola may contain up to 2% distinctly green seeds and a maximum of 5% damaged seed (including green).
- The allowable limit for No.2 is 6% distinctly green and 12% total damaged seed.
- The allowable limit for No.3 is 20% distinctly green and 25% total damaged seed.
- Anything above that is sample.
What is ‘Distinctly green’ (DGR)?
The Canadian Grain Commission has a colour guide for graders. Look under the distinctly green (DGR) section in the guide for an email to order one. Also read the Canadian Canola Growers Association’s Know Your Grade. DGR is dark green throughout the whole seed.
Graders cannot include light green or greenish yellow seeds – sometimes called ‘limes’ – in the distinctly green total. But if a lot of seeds are lime coloured, this can factor into the overall evaluation of colour. Without the “good natural colour” required for No.1, graders can downgrade the canola. (Read the Colour section in the Grain Grading Guide.)
What is ‘Damaged seed’ (DMG)?
The Grain Grading Guide describes damaged seed (DMG) as distinctly shrunken or shriveled; badly discoloured from mould; completely and densely covered with rime; excessively weathered, sprouted, tan coloured, distinctly green, heated, insect damaged or otherwise damaged. Damage is severe and obvious.
Know your green count
When shopping around for buyers, know the green count and use a representative sample. Elevators and processors can reject loads that don’t meet the specifications indicated in the original sample. Growers can send samples to the Canadian Grain Commission’s Harvest Sample Program, which provides dockage, oil, protein and chlorophyll content for canola.
Get more than one opinion
With a grade-reducing amount of green seed, talk to grain buyers to see if your green count assessment matches what they find, and ask around for potential blending opportunities if the percentage is high. Distinctly green is a subjective analysis, requiring graders to decide whether marginal lime green seeds count as ‘distinctly green’ or not. The Canadian Grain Commission has a process to challenge a grade.
Primary causes for green seed
Frost
Most green seed issues result when heavy frost hits canola before the seeds mature. This permanently stops the chlorophyll-clearing process and locks in green. Nothing can be done to reduce this green.
If frost is forecast, should farmers cut canola ahead of the frost – even if the canola is green? Swathing too early in anticipation of a frost is rarely a good move. To be effective, growers need to swath three good curing days ahead of the frost. This early swathing can backfire because it locks in a yield loss (because most seeds are not physiologically mature) in anticipation of a heavy frost that may not occur.
Not frost
Late-season hail, cutting in hot, dry weather and cutting the crop too green can lead to high green counts in the sample. Basically anything that stops canola from physiologically maturing properly can lead to high green.
–Cutting too green
Cutting canola before all seeds are firm can lead to higher green counts. The ideal timing is when 60 per cent, or more, of seeds on the main stem are showing signs of colour change and all sides on side branches are “firm to roll”. (They roll between thumb and forefinger without squishing.) This cut timing is good for maximum yield, and also reduces the green risk.
–Cutting in hot weather
Cutting canola on a hot day can lead to extra fast curing, which can trap green in the seeds. The de-greening process can restart in swathed canola after rainfall re-wets pods and seeds. (More on the that in the next section.) But the lower-risk option could be to delay swathing until highs are not “hot” or until seeds are more mature.
Risk of green seed is low on plants swathed when seed colour change approaches 60 per cent on the main stem, and the plant doesn’t have many side branches. However, if the crop has large plants with multiple branches, and if seed colour change has not started on the side branches, swathing on a hot day will be higher risk for green seed. Note that hot humid conditions are more favourable for green-clearing function than hot dry conditions.
Reducing green levels
Frost
Frost stops the chlorophyll-clearing process in canola seed. High green counts are likely in fields not fully mature when the frost occurred. But how bad was the frost? In fall, hardened canola may tolerate as low as -4°C for a few hours. If growers can leave canola standing after a frost, green-clearing not stopped by the frost can continue. Waiting may also cause seeds in severely damaged pods to shell out. This will likely reduce overall yield but could increase grade if seeds in top pods have a high green count.
Monitor these fields regularly to make sure shattering losses are not excessive. If shattering is minimal, the extra time before swathing or combining could benefit chlorophyll reduction. If shattering, swathing may help preserve the yield – but again, high green will reduce the grade.
Not frost
High green counts that result from causes other than frost could drop with enough time and moisture. But this only occurs if canola is left in swaths, not in the bin. The enzyme process to clear chlorophyll could resume when canola seed moisture gets back up to 20 per cent and temperatures remain at 15°C or warmer. Several days of heavy dew, high humidity and rain events may be required. Note that if green counts are high and seed moisture is also high, the crop may still be curing.
In 2024, CCC agronomy specialist Ian Epp saw a big drop in green in one of his own fields in north central Saskatchewan. The field experienced hail damage on September 10. When they first started combining the hail damaged field, the canola had 12 per cent green. So they waited. After a few humid days and half an inch of rain, they tried again and the sample had dropped to less than two per cent green.
Will green seed go down in the dryer?
Drying can shrivel up green immature seeds, which might seem to have a benefit, but it does not reduce the green in mature seed.
Will green content go down over time in storage?
Some researchers found that long-term storage may decrease green seed count slightly, but significant movement – enough to improve grade – is not likely. (See Table 1 in the Green seed section under Factors impacting canola storage.)
Storage risks
Research shows that green canola seeds can increase the storage risk, even if canola is dry and cool. It could be that small shrivelled canola seed, which often comes with high green seed, can mean smaller air pockets between seeds in the bin. Smaller particles will increase the resistance to air flow. This makes it even more important to leave the fan on as it will need to work longer to cool the entire bulk.
Canola with high chlorophyll content is less stable in storage, even if the canola is dry and cool. The safest bet is to deliver sooner than later. If that is not an option, monitor it closely.
