ARCHIVED - Red lentil grading changes guided by research

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In 2010, a wet and cool growing season in Western Canada led to an increase in 3 grading issues in red lentils – bleached, copper-coloured and rinkled seeds.

The red lentil industry asked the Western Standards Committee to investigate how these issues affected dehulling and end-use quality.

On August 1, 2012 new grading specifications for red lentils came into effect based on recommendations from the Western Standards Committee. Scientific research, combined with input from Canada’s grain industry, guided the changes in red lentil grades.

Grading issues investigated

Bleached seeds

Bleached seeds have a whitened seed coat that is distinctly faded from the natural red colour of sound lentils. The discoloration must affect the entire seed coat. Lentils having a lighter pink shade that are contrasting with the overall sample are considered sound.

Copper-coloured seeds

Copper-coloured seeds in red lentils have a rust colour that covers both sides of the seed and the entire seed coat. This rust colour contrasts distinctly with the natural red colour of red lentils that are considered sound.

Wrinkled seeds

Wrinkled seeds in red lentils have sharp ridges and pronounced depressions such as folds and indents in the seed coat. Wrinkles may only occur on one side of the lentil. Seeds with dimpled coats or folds that are only seen on the outside of the ring of the seed are considered sound.

Impact on dehulling

Red lentils are mainly processed by being dehulled or split in half. Dehulling involves removing the seed coat and is an important part of processing because it improves the palatability and taste of red lentils and makes cooking red lentils faster.

Processors are concerned with how well or efficiently a red lentil can be dehulled. Bleached, copper-coloured and wrinkled seeds can affect the efficient dehulling of red lentils and the quality of the end product. Quality factors such as bleached, copper-coloured and wrinkled seeds can make dehulling more difficult and could mean greater expense, lost time and lower yield for lentil processors.

Research methods

The Canadian Grain Commission's Industry Services and Grain Research Laboratory looked at the effect of bleached, copper-coloured and wrinkled seeds on the dehulling quality of red lentils.

Sourcing red lentil samples

The first part of the study included sourcing red lentil samples affected by these grading issues. Industry Services inspectors sourced red lentil samples from Western producers through our Harvest Sample Program. From the samples, inspectors manually picked out red lentil seeds that were bleached, copper-coloured or wrinkled and made samples that contained varying levels of severity for each grading factor. The Grain Research Laboratory used these samples to study how each factor affects the dehulling quality of red lentils.

Tempering and dehulling

Each sample underwent the dehulling process. The first step of the dehulling process is tempering, which includes placing the samples in plastic containers. Water was added to each sample to bring the moisture to 12.5%.The containers were then sealed and kept at room temperature for 24 hours. Researchers occasionally shook the containers to ensure equal moisture distribution.

The tempered samples were then processed in a mill to dehull the red lentils, which involves removing the seed coat. The lentils were then put through a sieve and a Carter dockage tester. Researchers separated the materials into 3 different groups: dehulled seeds; seeds that were not successfully dehulled; and broken seeds and any powder that resulted from the milling. Researchers determined the amount of dehulled seeds and came up with percentages to measure how efficiently red lentils could be dehulled with varying amounts of each grading factor.

Research findings and grading changes

Bleached and copper-coloured seeds

samples with more than 5% bleached seeds showed significant difference in dehulling efficiency compared to those with 0%.

Figure 1. Effect of bleached seeds on dehulling efficiency

Chart shows the effect of bleached seeds on dehulling efficiency. Details in table below.

% Bleached seeds Dehulling efficiency (%)
Sample 1 Sample 2 Sample 3
0.0 77.2aFootnote 1 77.9a 73.6a
2.0 76.7a 77.4ab 73.1ab
5.0 76.3ab 77.3ab 73.1ab
10.0 74.9b 76.3bc 72.2bc
20.0 74.5b 75.2cd 71.2cd
30.0 72.9c 74.5d 70.8d

Samples with no copper-coloured seeds had an average of 16% higher dehulling efficiency, compared to samples that had 100% copper-coloured seeds. Samples with more than 2% copper-coloured seeds showed significant difference in dehulling efficiency compared to samples with 0%.

Figure 2. Effect of copper-coloured seeds on dehulling efficiency

Chart shows the effect of copper-coloured seeds on dehulling efficiency. Details in table below.

% Coppered seeds Dehulling efficiency (%)
Sample 4 Sample 5 Sample 6
0.0 72.0aFootnote 1 77.1a 77.9a
2.0 71.4ab 76.5ab 77.7a
5.0 70.4b 75.4b 76.0b
10.0 69.8bc 74.4bc 75.1bc
20.0 67.9c 72.8c 74.3cd
30.0 66.8d 71.6d 73.1d

New grading tolerances for bleached and copper-coloured seeds

The findings for bleached seeds and copper-coloured seeds were used to set the grading tolerances.

Table 1. Tolerances for copper-coloured and bleached seeds for red lentils
Grade name Copper-coloured Total bleached and copper-coloured
No. 1 Canada 1% 3%
No. 2 Canada 3% 10%
Extra No. 3 Canada 10% 25%
No. 3 Canada no limit no limit

Wrinkled seeds

It was observed that wrinkled seeds are more fragile than sound red lentils. The greater the percentage of wrinkled seeds in a sample, the greater the amount of broken seed fractions and powder, leading to a corresponding decrease in dehulling efficiency.

Figure 3. Effect of the level of severity of wrinkled seeds on dehulling efficiency

Chart shows the effect of wrinkled seeds on dehulling efficiency. Details in table below.

Severity Dehulling efficiency (%)
Sample 7 Sample 8 Sample 9
Sound 82.5aFootnote 1 56.7a 80.6a
Light-wrinkled 79.8b 55.9ab 79.6ab
Medium-wrinkled 75.1c 53.7b 78.0b
Severe-wrinkled 70.7d 50.3c 76.2c

New grading tolerances for wrinkled seeds

The findings for wrinkled seeds were used to set the grade tolerances.

Table 2. Tolerances for wrinkled seeds in red lentils
Grade name Damage
Heated (%) Peeled, split and broken (%) Other damage (%) Total damage (%) Wrinkled (%) Total damage including wrinkled (%)
No. 1 Canada 0.2 2 1 2 2 4
No. 2 Canada 0.5 3.5 2 3.5 5 8
Extra No. 3 Canada 0.5 5 5 5 n/a n/a
No. 3 Canada 1 10 10 10 n/a n/a

Did you know?

The Western Standards Committee is made up of grain producers, processors exporters and other members of the grain industry. This group studies and reviews grain grading issues. It is responsible for reviewing Canada's grading system to make sure it continues to be relevant and meets the needs of the grain industry and buyers of Canadian grain. Based on its studies and reviews, the Western Standards Committee makes recommendations to the Canadian Grain Commission for standards and specifications for grain grades.

The Canadian Grain Commission's research, combined with input from Canada's grain industry, guides grade changes for other pulse crops, such as peas and beans, as well as for wheat, barley, oats, canola, flax and other grains.


Bleaching is an indication of exposure to wet conditions at or near maturity. Bleaching is caused by alternate wetting and drying of grain which causes tiny fissures to develop throughout the kernels. The fissures are caused because the grain swells a little when it is wet and doesn't dry back to the same size.
Copper-coloured seeds have a rust color covering both sides of seed and the entire seed coat. The rust colour is in distinct contrast with the natural red colour of sound lentils.
A sample is a portion of grain taken to represent an entire truckload, carload or cargo.
Wrinkled seeds are characterized by a seed surface that has sharp ridges and pronounced depressions that could also be described as seed coat folds and indents. Wrinkles may be evident only on one side of the lentil. Lentils that only have dimpled seed coat or folds restricted only to the outside ring of the seed are considered sound.

Request a guide

Red lentil colour guides and wrinkled guides are provided, on request, to grain companies licensed by the Canadian Grain Commission. To receive a red lentil colour or wrinkled guide, please contact:

Daryl Beswitherick
Program Manager, Quality Assurance Service
Canadian Grain Commission
Telephone: 204-983-4627


Footnote 1

Means within a column with the same letter are not significantly different (p>0.05) as determined using Duncan's multiple range test.

Return to footnote 1 referrer