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Pre-harvest activities can impact red lentil quality

As the number one exporter of red lentils in the world, there is a lot on the line for producers when it comes to marketing a quality product. Plant breeder Bert Vandenberg at the University of Saskatchewan’s Crop Development Centre explains that about six years ago when significant amounts of red lentil were being exported for the first time, millers had difficulty with the product.


March 18, 2010
By Bruce Barker

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As the number one exporter of red lentils in the world, there is a lot
on the line for producers when it comes to marketing a quality product.
Plant breeder Bert Vandenberg at the University of Saskatchewan’s Crop
Development Centre explains that about six years ago when significant
amounts of red lentil were being exported for the first time, millers
had difficulty with the product.

26-13frame17  
Research has shown that proper timing of lentil desiccation will help to ensure a high-quality seed sample. (Photo by Emily Watson)  

They found that the higher moisture
content in the seed made the seed coat difficult to remove, and
approximately 95 percent of the red lentils consumed in the world are
consumed with their seed coats removed, mostly in soups and stews.
“Part of the problem was that our red lentil production system was
based on green lentils, where the objective was to keep the moisture at
14 percent so that the seed coat stayed on,” explains Vandenberg.
“That’s the opposite of what we want with red lentils, so we need to
treat them like a different crop than green lentils.”

With a red lentil harvested at 14 percent moisture, millers became
frustrated trying to remove the seed coat, and their milling yields
were lower. As a result, western Canadian red lentils would often be
purchased at a discounted price.

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To better understand how to produce a red lentil with better milling
quality, Vandenberg and graduate student Jesse Bruce conducted a
two-year research study looking at the effect of pre-harvest
treatments, such as swathing or desiccation on milling quality of red
lentils. They grew eight red lentil varieties at Rouleau and Floral,
Saskatchewan. The varieties, in order of increasing seed size were CDC
Robin, CDC Imperial CL, CDC Rosetown, CDC Blaze, CDC Impact CL, CDC
Rouleau, CDC Redberry and CDC Red Rider.

Each variety received pre-harvest treatments consisting of swathing at
early, recommended (bottom third of the plants at the pod rattle stage)
or late stages of maturity; and desiccation with Reglone at early,
recommended, and late stages. Seed samples were cleaned and sized over
roundhole and slotted screens, and the two most common fractions on
each type of screen were retained.

The samples were stored so that seeds eventually had 12.5 percent
moisture, which is considered the ideal moisture content for milling
red lentils according to research conducted by Dr. Ning Wang at the
Grain Research Laboratory in Winnipeg. The samples were passed through
both a Satake laboratory dehuller and a Turkish table top dehuller.

Milling quality was assessed according to three criteria. The first was
milling efficiency, which was the percent split and unsplit of the
total sample after removal of seed coats, flour and small broken
pieces. The second was dehulling efficiency where the percent of seeds
with complete seed coat removal was measured. The final was football
recovery, which was the percentage of dehulled but unsplit seeds. 

Vandenberg says that at three of four sites (Rouleau in 2005 and ’06,
and Floral in 2006), ideal warm sunny weather lasted all through
harvest. With these, the milling results were similar with all
treatments. The Floral 05 site had unfavourable harvest weather with
high humidity and intermittent rainfall throughout harvest and into
September.  Under the unfavourable conditions, the research did
highlight some differences. “We saw that under good conditions there
really wasn’t much difference, but with cool, wet conditions, milling
quality declined with early desiccation,” explains Vandenberg.


Milling efficiency and dehulling efficiency similar between treatments

Under good harvest conditions, both milling efficiency and dehulling
efficiency showed no effect of swathing or desiccation. Almost all
varieties were in the 85 to 90 percent range for milling efficiency;
millers aim for efficiencies above 80 percent to be economical, and 85
percent makes them happy.

Similarly, under good harvest conditions, dehulling efficiency reached 97 to 99 percent, with no difference in treatments. 

However, when the weather was cool and wet, early desiccation
significantly reduced milling efficiency to below 70 percent. Early
swathing under the same cool, wet conditions, though, still maintained
milling efficiency above 85 percent, while the other preharvest
treatments had milling efficiency just below 80 percent.

Vandenberg says that significant variety effects were also evident
under cool, wet conditions. CDC Robin and CDC Imperial CL were around
74 percent milling efficiency, while all the other varieties were in
the 78 to 82 percent range.

When harvest was cool and wet, the range of dehulling efficiency
dropped to 91.5 from 98.7 percent. Early desiccation was worse than all
other pre-harvest treatments, with only 90.5 percent seed coat removal,
and early swathing was the best at 98.8 percent. Once again, the
varieties with the smallest seeds, CDC Robin (92.1 percent) and CDC
Imperial CL (91.5 percent) had significantly lower dehulling efficiency
compared to all other varieties in the cool, wet harvest year.


Similar observations for football recovery

Under ideal harvest conditions, all pre-harvest treatments milled with
the Satake dehuller resulted in about 80 percent of the sample in the
form of footballs. When harvest was cool and wet, the percent football
recovery dropped from an overall 80 percent to about 50 percent.
Vandenberg explains that the wetting and drying cycles of intermittent
rains caused severe reduction in football recovery. The most effective
treatment for high football recovery was early swathing.


Good agronomics can help overcome weather

While the weather can not be controlled, Vandenberg says that red
lentil producers can look after agronomics in order to help beat the
weather. Early seeding and avoiding herbicide crop injury that delays
maturity will help to minimize the risk. But late seeding and delayed
maturity from herbicide injury can delay harvest into the second and
third weeks of August when weather conditions can start to get dicey.

Should harvest weather go bad, though, careful desiccation timing can
still improve the chances of maintaining milling quality. Wait until at
least the recommended stage (bottom third of plants at the pod rattle
stage) to ensure that milling quality is not compromised. Early
swathing also resulted in better than average quality than early
desiccation with Reglone. “It comes down to prudent risk management.
Make sure you do everything you can to get the crop off early,” says
Vandenberg.  “Then if you get caught by poor harvest weather, make sure
desiccation is timed properly.”