Safely storing higher-oil canola seed
By Carolyn King
Spoilage problems in storage can take a big bite out of a grower’s economic returns for canola. With the trend to higher oil content canola, growers are wondering if the requirements for safe storage might be different from those for regular canola.
A recently completed preliminary study in Saskatchewan and a longer-term study in Manitoba are working towards answering that important question.
Making sure storage guidelines are up to date
In a phone survey of about 1,050 producers across the Prairies in 2009, the Canola Council of Canada (CCC) found that over a third of respondents had encountered a problem with canola spoilage in storage on their farms at some point over the years.
“Those results were a bit of an eye-opener for us,” says Kristen Phillips, CCC agronomy specialist in Manitoba. “That’s part of the reason we’ve had a focus on both research into updating the safe storage temperature and moisture recommendations, and also extension to really try to drive home the importance of conditioning canola, so growers get the seed down to safe moisture and temperature conditions if they are planning to keep it in the bin for a few months.”
One of Phillips’ areas of specialty is harvest and storage management. She identifies several trends that are driving the need to ensure up-to-date storage guidelines. One trend is that more growers have higher oil content canola. The Canadian canola industry is approaching its goal to increase canola’s average oil content from 42.5 per cent in 2006 to 45 per cent in 2015. For instance, for No. 1 canola from Western Canada, the five-year average oil content for 2007 to 2011 was 44.4 per cent. (In 2012, the average was 43.5 per cent, relatively low due to a combination of temperature, moisture and disease conditions.)
“Some research in other countries, most notably Australia, has found a difference in terms of safe combinations of temperature and moisture for higher versus lower oil content canola,” notes Phillips. “That information suggests a higher oil content may make canola a little more susceptible to spoilage in storage, but we need research under Prairie conditions to be more definitive on how much the recommendations should change with higher oil content.”
Another trend is that more farmers are using larger bins, which could affect such factors as the possibility of compression damage to the seeds, and the ability of the grain mass to insulate and trap heat in the bin.
Phillips also sees certain trends that might in some cases cause growers to store their canola for longer periods, increasing the possibility that spoilage could eventually occur. “With the changes to the Canadian Wheat Board, it is conceivable that in some situations on some farms, growers may now look at marketing their cereals earlier to meet their cash flow requirements, and may hang on to their canola for a longer time to capture pricing opportunities.
“Also with the high-stability oil varieties of canola for the trans fat-free frying market, there are often some limitations on when they can be delivered. That sometimes leads growers to store at least a portion of that production for a longer time. And as the breeding programs look to increase the oil content of those varieties, it’s that much more important to know the implications for safe storage conditions,” adds Phillips. “High-stability canola is a higher value product, so the penalty for losing quality in storage is that much bigger.”
Preliminary study raises some questions
The Prairie Agricultural Machinery Institute (PAMI) conducted the recently completed study in Saskatchewan. This lab study had two components: testing the compression effects of storage in tall bins; and evaluating the effects of temperature and moisture content on stored canola. The study was funded by SaskCanola, Saskatchewan’s Agriculture Development Fund and PAMI.
With more farmers using larger bins these days, the PAMI researchers were interested in evaluating the compression effects on high-oil and regular canola seeds stored in tall bins. The high-oil sample they obtained had 47.4 per cent oil content, while the regular sample had 45.3 per cent, so the difference in oil contents between the samples wasn’t as large as they had hoped. They tested the high-oil sample at 7.3 per cent and 10.5 per cent moisture content, and the standard sample at 5 and 8.4 per cent moisture content. They incrementally added weights on top of each sample to simulate the force applied by the weight of a column of canola seed stored in a bin up to 100 feet high.
The four samples were evaluated for germination, seed damage and deformation, and oil exudation. None of the samples showed any negative effects due to the compression.
“Some studies in other countries had indicated that higher oil content canola was compressing, especially in tall bins, but our results didn’t bear that out. Of the samples we tested, there wasn’t a significant difference in compressibility,” says Nathan Gregg, a project manager with PAMI.
However, he cautions, “This isn’t a definitive result. It wasn’t a multiple replicated trial, so there might be varietal differences or differences in moisture contents, temperatures and so on that could have an effect in conjunction with a higher oil content.”
Phillips also reminds growers that, whether or not further testing confirms compression is not an issue, storing canola in taller bins still requires special attention. “The greater depth of the seed in taller bins means greater static pressure and that means more resistance to airflow through the seed when it comes to aeration.”
In the study’s other component, the PAMI researchers tested four categories of canola: high oil (47.4 per cent oil content), high dockage, high green count, and standard clean canola. The researchers conditioned the samples to seven moisture contents (7, 7.5, 8, 8.5, 9, 10 and 11 per cent) and then stored them in small-scale chambers at five temperatures (-5, +5, 15, 25 and 35 C).
They monitored the temperature within each sample to watch for heating as an indicator of spoilage. Although they didn’t detect any increase in sample temperature, some samples were visibly mouldy when removed from the chambers after two months.
The samples were tested for several oil-quality characteristics related to spoilage, such as acid value and free fatty acid level. The results suggested that oil quality in the samples had deteriorated somewhat but had not necessarily gone beyond industry-acceptable limits over the two months. However, the trends in the results were not firm enough to develop moisture content and temperature guidelines based on oil content.
Despite additional testing to examine the methods used in the tests, the researchers weren’t able to conclusively explain some aspects of the results. In particular, Gregg is concerned that they hadn’t detected heating in the mouldy and deteriorating oil-quality samples. He points out, “Farmers rely on heating as an indication of spoilage. If temperature isn’t an accurate or timely indicator, then that’s a big problem.” He would like to see further investigation to clarify to what extent grain temperature is a reliable early indicator of different spoilage processes.
Even if it turns out that early steps in spoilage processes aren’t necessarily signalled by a temperature change, Phillips thinks temperature monitoring in larger bins is still a valuable practice for obtaining information on current conditions in the bin. “My concern would be if the PAMI researchers had found heat-damaged seed, which is a big downgrading factor for the grower, without a shift in the temperature. I would like to see them explore that a little further, and determine if that was the case.”
Phillips adds that grain monitoring technology is advancing and many companies now offer monitoring cables with sensors for both moisture and temperature, which would shed more light on the actual conditions within a bin.
“As the oil content of any crop increases, the percentage amount of other material – protein, carbohydrate and fibre – in the grain is less. Oil does not absorb moisture; only the non-oil materials absorb moisture. So you would expect that, as the oil content increases, the grains would spoil faster at much lower moisture contents,” explains Dr. Digvir Jayas, a grain storage specialist in biosystems engineering and vice-president (research and international) at the University of Manitoba.
Jayas is leading the Manitoba study, which is expected to finish this year. One of the objectives of this lab study is to develop moisture and temperature guidelines for safe storage of high-oil canola. The study is funded through the Canola/Flax Canadian Agri-Science Cluster. The other members of the research team are Dr. Noel White with Agriculture and Agri-Food Canada, and Dr. Fuji Jian, Chelladurai Vellaichamy and Ke Sun at the University of Manitoba.
The researchers are testing three high-oil hybrids at four initial moisture contents (8, 10, 12 and 14 per cent) and stored at four temperatures (10, 20, 30 and 40 C) in small-scale chambers with controlled temperature and humidity conditions. The three hybrids are NX4-105 (45.4 per cent oil content), InVigor 5440 (47.1 per cent) and 45H29 (45.4 per cent).
During the 20-week storage period, samples were tested regularly to evaluate the degree of spoilage based on germination, mould and free fatty acid value.
The results so far indicate NX4-105 and InVigor 5440 samples could be safely stored for 20 weeks at 10 or 20 C at all of the moisture contents except 14 per cent. However, for 45H29, the samples at 12 or 14 per cent moisture content were already in poor condition after two weeks of storage at 10 or 20 C. The researchers are doing further tests with new samples to see if 45H29 requires special attention for storage or if the early spoilage was due to a problem in the particular sample used.
As expected, spoilage was greater at 30 and 40 C. According to the germination tests, high-oil canola at 8 per cent moisture content should be stored for less than 12 weeks at 30 C and less than four weeks at 40 C. At 10 per cent moisture, it should be stored for less than six weeks at 30 C and less than two weeks at 40 C. At 12 or 14 per cent moisture, high-oil cannot be safely stored at 30 or 40 C.
Based on the results so far, Jayas advises, “Eight per cent should be the recommended moisture content for storing canola; 10 per cent would not be safe for long-term storage.” The criterion of this safe storage recommendation is either a 20 per cent drop in germination from its initial value or the appearance of visible mould.
Jayas also notes, “Under the current guidelines, farmers are not penalized if they sell canola at 10 per cent moisture content. So they usually try to store it at close to 10 per cent, even though there’s a greater risk of spoilage. If they stored it at 8 per cent, then it would have 2 per cent less moisture and they aren’t compensated [for the lower tonnage]. As an industry, I think we should seriously look at perhaps giving farmers a premium if they reduce the moisture content to 8 per cent, because the canola would then have a longer storability.”
Although the CCC hasn’t explored this idea of pricing based on moisture content, Phillips thinks it might be a challenge to come up with a universal recommendation that fits every situation. “From a grower’s standpoint, the benefit of a lower moisture content for maintaining quality in storage comes if you’re planning to store it over a longer term. If you’re planning to deliver it relatively soon, then [being able to sell it at between 9 and 10 per cent moisture] gives you the opportunity to harvest a little sooner.”
Phillips adds, “I think it comes down to the growers having a good relationship with the companies buying their seed. The quality of the seed that you’re delivering is always part of the negotiation, and part of that quality is the moisture content that it’s been taken off at.”
She is leery about the idea of adding moisture to drier canola seed to raise the moisture content closer to 10 per cent and bring the weight up. “It might add some value, but it might instead be detrimental if you lose a grade or two on a portion of your seed.”
For now, for safe longer-term storage of higher-oil or regular canola, 8 per cent moisture content or less is preferred. But Phillips emphasizes, “Canola is likely going to need some conditioning almost regardless of the moisture content, particularly these days.
“With larger farms and more acres to cover and the shift to larger equipment, we have really increased our capacity to harvest larger volumes of canola in a shorter period of time. Our combining capacity, in terms of the acres and tonnage per hour, is probably the greatest during the hottest parts of the day when the canola is the driest. So a big proportion of your grain is likely going to be at an elevated temperature. It’s important to condition it to bring down that temperature even if it is testing dry,” she says.
“We have certainly seen individual instances where canola coming off hot has started to heat [in the bin], even though it was down around 7 or 8 per cent moisture. When you get grain temperatures around 30 C or more, canola can be pretty unstable even at lower moisture contents.”
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