Storage of Canola

Last Update: Friday, June 20, 2014 1:52:46 PM

Table of contents

    Important Tips for Best Management

    • Storing the crop in a dry and cool condition reduces the risk of “sweating” and thereby reduce risk of economic losses from spoilage in storage.
    • 10% moisture content does not equal safe storage.
    • For storage longer than 5 months, canola should be binned at a maximum of 8% moisture and canola cooled to 15°C or lower throughout the bin.
    • Monitor bins closely during the first six weeks in storage and then continue to check stored canola regularly until delivery.
    • If stored canola temperatures plateau or start to rise while outside air cools through the winter, it can signal the start of spoilage.

     

    Aeration = cooling/conditioning  Aeration fans should be started as soon as the canola covers the floor of the bin, so that immediate cooling can take place. Fans must be operated continuously until the temperature of the canola is near the average outside temperature.

    • When the outside temperature has dropped below the temperature of the stored canola by 5 to 10°C, the canola should be cooled again.
    • No conditioning operation is complete until the temperature of the entire bulk has reached the desired level.
    • After the bulk has reached the desired storage temperature, the bin should be checked periodically for evidence of heating or moisture migration.
    • Airflow rates for aeration range from 0.1 to 0.2 cfm/bushel (1-2 L/s per m3)

     

    Natural air drying (near ambient drying) = reducing the moisture in the grain.  Natural air drying using aeration alone can remove one or two percentage points of moisture, but only if outside air has “capacity to dry.” Air’s capacity to dry depends on its temperature and relative humidity (RH).

    • The fans should be started as soon as the canola covers the perforated areas of the bin floor and should be operated continuously in the fall until either the crop temperature is reduced to 0°C or the crop is dry. If the air lacks enough capacity to dry to reach safe storage conditions prior to spoilage, heated air drying may be required.
    • Airflow rates for natural air drying range from 1 to 2 cfm/bushel (10-20 L/s per m3)

     

    Heated air drying= reducing the moisture in the grain with an additional heat source.  Canola destined for seeding purposes should be dried at less than 45°C; however, for oil extraction, seeds can be dried at up to 82°C

    • A wetter seed requires a longer drying process at a lower drying temperature.
    • Grain must be cooled after heated air drying.

     

    Grain bag storage tips:

    • Store only dry seed.
    • Store for short duration (3-6 months).
    • Monitor with temperature probes at least twice per week until temperatures stabilize.
    • Watch for rodent activity.
    • Clear snow to help prevent deer from walking on bags
    • Place in well-drained area.
    • Unload before frost goes out of ground in spring.
    • Place on grass to prevent stubble from poking holes in the bag.
       


    Storage of Canola

    Factors affecting canola quality during storage include:

    • seed maturity and condition;
    • seed moisture,
    • temperature,
    • oil content
    • elapsed time in storage,
    • molds, insects, and mites,
    • dockage,
    • cultivar type,
    • weather during storage period, and
    • the storage structure and handling methods used.


    How Condition of Harvested Seed Affects Safe Storage

    Seed Maturity and Condition

    The original condition of a grain lot at harvest is probably the most important factor affecting its storability. Freshly harvested canola can display a high respiration rate for up to 6 weeks before becoming dormant.  This process is often referred to as "sweating". Fully ripened seeds of low moisture content are metabolically dormant and respiration is negligible. The apparent respiration of freshly harvested and stored grain has been well researched and is predominantly due to the growth of micro-organisms such as fungi.

    Sweating= heat and moisture respired during final ripening of immature seeds from late branches, immature weed seeds and other dockage, and from field fungi normally found on grain.

    Sweating may also be caused by convection currents that develop quickly within bins with grain from different loads of varying moisture and temperature deposited at different levels within the bins. Dockage is known to accumulate at bin walls during unloading and can be significantly higher in moisture (Prasad et al., 1978) Some researchers (Pronyk et al., 2004; Sinha and Wallace, 1977) have monitored freshly harvested canola in steel bins and found no evidence of an initial sweating process. Regular monitoring is required because increases in heat and moisture favour the growth of storage molds. Mold growth and respiration produces additional heat and moisture and then the temperature within the seed bulk escalates quickly. Eventually the seeds may become heat-damaged.

    Storing the crop in a dry and cool condition reduces the risk of sweating.

    Stored green seed

    Immature seeds are distinctly green when crushed. Based on crushed seed examination, No. 1 and No. 2 Canada Canola Grades may contain a maximum of 2.0 and 6.0% distinctly green seeds, respectively (Canadian Grain Commission, 2012).

     
    Table 1. Primary Grade Determinant Canola, Canada
      Damage
    Grade Name Distinctly Green % Heated % Total %
    No. 1 Canada 2 0.1 5
    No. 2 Canada 6 0.5 12
    No 3 Canada 20 2 25
    Grade, in No. 3 specs not met Canola, Sample Canada
    Account Damaged
    Canola, Sample Canada
    Account Heated
    Canola, Sampled Canada
    Account Heated

    Source:  Canadian Grain Commission. Effective Aug 1, 2012.

    Financial penalties are levied for distinctly green seeds in stocks offered for commercial sale because of added refining costs and adverse effects on the shelf-life of canola-based food products. Green seed is a problem when fields are harvested before the majority of seeds have turned color, when the crop was frozen, or when heat and drought stress occurred before maturity. During normal development, the green color disappears upon maturation but arrested development can result in chlorophyll retention.

    Leaving B. rapa canola in the swath for 4 days reduced the proportion of distinctly green seeds at harvest (Cenkowski et al., 1989a). Drying high moisture (>30% moisture) samples at 80°C is also effective in reducing the proportion of distinctly green seeds to less than 3%, however 20°C to 40°C are the best drying temperatures for samples containing less moisture. Long-term storage (five months) may slightly reduce the percentage of green seeds (Table 2). Several researchers (Cenkowski and Jayas, 1993; Johnson-Flanagan et al., 1994) have reported that rehumidification of green seed at moderate temperatures (20-25°C) can slightly reduce the chlorophyll contents; however this will predispose the lot to spoilage unless it is subsequently dried and cooled.

    Developing canola seeds are frequently affected by localized frost in the Canadian prairies. Occasionally, an early frost will cause damage over widespread areas. In late August 1982, a frost arrested seed development over much of the canola growing area of Manitoba and Saskatchewan. Approximately 38% of the total crop was graded No. 3 Canada (3CR) or Sample Account Damaged compared to 4% of the crop in these grades in 1981. Most of the 1.16M tonnes of frost-damaged seed produced in 1982 was not readily marketable and required storage over winter. Quality changes were observed in 60 bins of farm-stored canola monitored within a 200-km radius of Winnipeg, Manitoba from November 1982 to April 1983. In November, the contents of one bin reached 102°C with steam observed arising from the centre surface; corresponding temperatures for non-heating bins were 8 to 13°C. Generally, the quality of seeds in official grades 2CR, 3CR and Sample Account Damaged did not decline in storage. The percentage of green seeds declined slightly in 28 bins of B. napus examined during the storage period (Table 2). Spoilage and heating problems in frost-damaged canola are most likely to occur during the first months of storage and can be prevented by use of aeration, careful bin management with frequent monitoring, and the use of small, readily accessible granaries (Mills et al., 1984).

    Table 2. Changes in the Level of Frost Damaged Green Canola Seed During Storage
     % Green Seed
    Seed Grade Early November Mid April
    Canada No. 2 4.3 4.4
    Canada No. 3 8.0 6.6
    Sample 18.2 17.6


    Occasionally, canola crops are covered by snow before they can be harvested. In October 1984, a large amount of canola was covered by snow in Northern Alberta and seed was harvested the following spring. Samples of this canola were compared to samples of fall-harvested seed from the same area. Spring-harvested seed stored more poorly than fall- harvested seed, having greater increases in free fatty acids, conductivity (electrolyte leakage when placed in water) and storage (post-harvest) molds, and larger losses in viability (indicators of quality loss) when stored hermetically at 10% or 12.5% moisture levels (Daun et al., 1986).

    Seed Moisture

    The moisture level and temperature of the grain influences events that occur during storage and may lead to spoilage and self-heating.Canola and other high-oil seeds are more prone to deterioration in storage than cereal grains and must be stored at a lower moisture level to prevent molding.Under the Canada Grains Act, the maximum moisture at which canola can be sold as straight grade (dry) is 10% moisture (Canadian Grain Commission, 2012). Because seed with 10% moisture can be sold without penalty, such a figure is often assumed to represent a safe level (Moysey and Norum, 1975).

    10% moisture content ≠ safe storage.

    The upper safe relative humidity limit is 70% at moderate temperatures at which point molds begin to grow. This equates to 8.3% moisture for canola and 13.9% moisture for wheat (Triticum aestivum L.) at 25°C (Mills and Sinha, 1980; Hall, 1980). At high grain temperatures (30 – 40°C), mould can occur even when moisture contents are below 8% (Sathya et al., 2009) Both moisture level and relative humidity are dependent on temperature (Mills, 1989).

    Seed Temperature

    Temperature is important for three main reasons:

    • temperature and moisture influence enzymatic and biological activities and thus the rate of spoilage;
    • temperature differences within bulk commodities favor mold development through moisture migration; and
    • the high temperature of seeds harvested and binned on a hot day is retained within un-aerated bulks for many months due to the insulating effects of the bulk seeds (Mills, 1989).


    Canola in the swath, combine hopper, truck and bin can be several degrees warmer than ambient air on sunny days (Prasad et al.,1978).

    Temperature differences result in moisture moving from warmer to colder areas of the bin. During late fall, cold air sinks in the grain at the outside of the bulk and warm moister air, in the centre of the bulk, rises and condensation may occur when it reaches the cold seeds near the surface. This free moisture and warm temperatures near the surface can lead to rapid spoilage. In late spring and summer, it is possible to get moisture migration in the opposite direction if the outside temperature is warmer than the seeds. Warming action from the sun on the bin causes air to move up near the outside wall of the bin and down through the centre of the bulk. Moisture is reabsorbed by the cooler canola in the centre of the bin. Removing a portion of the seeds from the centre of the bin is a method of interrupting the increase in temperature and moisture in the central core. Friesen and Huminicki (1986) report that significant migration occurs in canola at moisture levels as low as 8% when placed into storage at high temperature and not cooled by aeration.

    Figure 1a. Air movement in bin, winter

    Figure 1b. Air movement in bin, spring

    Figure 1. Moisture Migration in Stored Canola

    Tip: For a quick test of

    restricted ventilation, open the lid at the top of the bin and feel if the expelled air is warm on your face.  If it is, ventilation and conditioning is required.

    Temperature/Moisture Interaction on Safe Storage Time

    Moisture level and temperature determine the safe storage period for canola; the storage time chart shown in Figure 2 predicts the keeping quality of canola over five months, under varying temperatures and moisture.

    If the temperature or moisture level of the canola falls within the spoilage area of the chart, either the seed moisture or temperature or both need to be reduced. Moisture level can be reduced either by delaying combining to allow further drying in the swath or by artificially drying the seed. Aerating the bin contents can reduce the temperature. If the seed is binned at above 25°C, or if pockets of immature seeds or green weed seeds are present, 8.3% moisture is too high for long-term, safe storage. For storage longer than 5 months, canola should be binned at a maximum of 8% moisture and cool temperature (Mills, 1989).

    Tip: Move one-third of the canola out of a full bin to disrupt the moisture cycle and help cool the mass when outside air temperatures have cooled.

    To successfully store canola for periods of 6 to 24 months, particular attention must be given to conditioning and monitoring. Quality seed may be stored 2 to 3 years if its moisture and temperature are properly maintained (Thomas, 1984).

    Figure 2. Canola Storage Risk Increases with Temperature, Mositure and Time

    Figure 2. Canola Storage Risk Increases With Temperature , Mositure And Time

     

    Moulds, Insects and Mites

    Moulds

    Seeds in storage provide a good substrate for storage molds, the most important cause of seed deterioration (Christensen and Kaufmann, 1969). Molds spores, occurring in the soil and on decaying plant material in the field, are coated onto the seeds during harvesting operations. Fungi common on freshly harvested canola (such as Alternaria and Cladosporium) tend to decline during early storage and if suitable conditions exist, spoilage fungi increase (Sinha and Wallace, 1977). Each species of storage mold flourishes at a different relative humidity level and temperature. Some species, for exampleEurotium amstelodamiMangin, grow at low humidities, affect seed germination, and produce water as a consequence of metabolism during their growth. Higher moisture levels enable more damaging molds to grow. These molds includeAspergillus candidusLink and Penicillium species, all of which impair seed germination and are often associated with hot spots - areas within bulk seed that have a higher temperature than the surrounding material (Mills, 1989).

    Molding and heating can occur very quickly in moist canola, and where this happens, the seeds are likely to clump together.

    There can be a marked increase in the level of free fatty acids, probably brought about by the growth of molds (Nash, 1978). Heated seeds are brown instead of a normal yellow color and produce a distinct tobacco-like odour in the oil and meal, which is difficult to remove by processing (Thomas, 1984). The result is that the quality of the stored product for processing is greatly reduced.

    The speed at which molding occurs in freshly harvested canola is important because it influences drying and storage management decisions. Research determined the spoilage time of freshly harvested rapeseed stored aerobically in tubes at five temperatures ranging from 5°C to 25°C and at seven moisture levels ranging from 6% to 17% at each temperature. (Burrell et al. (1980). Spoilage as expected was more rapid at higher temperatures and higher moisture levels. Seed clumping preceded the appearance of visible mold colonies and seed germination was affected much later. Seeds at 25°C and 10.6% moisture clumped together after 11 days and visible mold colonies appeared after 21 days, however germination was still unaffected after 40 days. This suggests that seed clumping (Table 3) is the best criterion for determining the maximum period available for drying before fungal growth because the appearance of the seed will have already deteriorated by the time fungal colonies become visible. (Burrell et al., 1980). Under normal harvest conditions, canola seed over 10% moisture should be dried within 1 - 2 weeks to avoid spoilage.

    Table 3.  Maximum Period (Days) Without Visible "Clumping" of Canola by Moulds Initial Moisture (%) Days Without Clumping
     Temperature °C
    Initial Moisture Content (%) 25 20 15 10 5
    17 4 4 6 11 20
    15.6 4 6 6 11 28
    13.7 4 6 11 20 46
    12.3 8 6 18 25 109
    10.6 11 18 42 42 238
    8.9 23 48 116 279 300
    6.7 69 180 300 300 300


    During 1974 to 1976, considerable spoilage and heating of stored canola occurred on western Canadian farms (Mills, 1976; Daun and Mills, 1979). Spoilage and heating of the 1974 and 1975 crops were reported by 19-25% of the managers of western Canada Pool elevators.

    Generally, crop districts with a high elevator spoilage coincided with districts of high incidence of farm spoilage and heating in 1974. The higher the seed moisture level, the higher the probability of spoilage and heating even with turning (moving grain from bin to bin during storage) (Mills, 1976). Monetary losses resulting from bin-heating of canola were estimated to be at least $Cdn 3 million for the 1975 and 1976 crop years.

    Insects and mites

    Insects occur in stored rapeseed bulks (Sinha and Wallace, 1977) but vary in their ability to survive and establish infestations. Primary stored product insects such as rusty grain beetle, red flour beetle and saw-toothed grain beetle can occasionally be found in stored canola if cereal grain or weed seeds are mixed in with the canola.

    On whole seed, the merchant grain beetle (Oryzaephilus mercator(Fauvel)) was able to multiply 1.87 times in 12 weeks, but the rusty grain beetle (Cryptolestes ferrugineus(Stephens)) failed to complete its life cycle. Generally, whole seeds are less vulnerable to infestation than crushed seeds and only a few insect species are adapted to the high oil content of rapeseed (Sinha, 1972). The optimum temperature for rapid growth of insects is in the range of 30°C to 35°C; their activity is greatly retarded by temperatures below 18°C. If bulk seed is cool and dry, insects will not thrive.

    However, seed may go into storage at acceptable levels of moisture and temperature and then at a later date develop pockets of high moisture and temperature suitable for insect activity (Muir, 1973). Infestation of binned seed by insects and mites will reduce the safe storage times shown in Table 2 (Mills and Sinha, 1980).

    Mites carry mold spores in and on their bodies. Mites may eat the surface and interior of canola seeds affecting seed weight and quality (Hudson et al., 1991) and often feed on molds; heavy contamination by some mite species will leave a distinctly minty odor (Mills, 1989). Sinha and Wallace (1977) found that canola was more vulnerable to pest infestation than barley (Hordeum vulgareL.) when stored in farm bins in Manitoba, Canada during 1973-76. Unlike barley, canola was heavily infested by grain mites and their predators. It was suggested that the prey mites multiplied by feeding (probably selectively) on fungal species and dockage (grain dust, broken grain kernels, weed seeds, etc.). The prey mite populations were effectively checked by predatory mites favored by low temperatures during the cooler months. Turning canola in the spring reduced temperature and moisture differences between the warm centre and cooler edges, but also dispersed mold spores and mites throughout the bulk.

    The distribution of the three most important British genera of stored-product mites in bulks of canola, wheat, and barley at a range of relative humidities was studied over a 10 year period. (Armitage (1984). In winter, in both aerated and non-aerated bulks, grain feeding Acarus and Glycyphagus spp. were frequently present on seed surfaces dampened by moisture. In summer, the mites were usually most abundant below the surface, regardless of the relative humidity of the bulks. The difference between summer and winter distributions appeared to be related to the drying of the surface layers during the spring and summer; this may have caused the mites in those layers to reproduce less quickly. Populations of the predatory mite (Cheyletus eruditus(Schrank)) were usually more evenly distributed than those of Acarus and Glycyphagus and appeared less sensitive to seasonal moisture and temperature changes. Aeration of 9% moisture seeds, at air temperatures below 5°C for 4 months, reduced the population of Acarus spp. to 4000 per kg, compared to 36,000 per kg in non-aerated bins.

    Molds, insects and mites occurring in grain bulks seldom act alone but interact with the grain and with each other. High populations of molds and mites often co-occur and interact together in farm-stored rapeseed. (Fleurat-Lessard,1973; Sinha and Wallace, 1977).

    Tip:  Turning the grain in the winter will reduce the temperature and thus deter insect growth.


    Controlling insects

    Insecticidal control

    There are several products available such as aluminum phosphide to treat insect infestations in canola bins. A registered diatomaceous earth product can be used to treat empty bins, but should never be used directly on canola seed as the product will not be effective.

    Keep Your Canola Export Ready: Do not use malathion on canola before or during storage or in the empty bins where canola will be stored. If the bin was treated previously, do not store canola in bins within six months of treatment. Malathion is lipophilic which increases the risk of absorption by oilseeds as compared to other grains like cereals, hence the need for taking these precautions.

    Heat

    Insects exposed to a grain temperature of 50 degrees C for about 15 minutes will be killed.  If canola requires heated-air drying, this may be an effective option.

    Cold

    Prolonged exposure to cold temperatures will kill most insects. However, grain bins over six metres (20 feet) in diameter will not cool sufficiently on their own to control some insects. To ensure the entire volume gets sufficient cold exposure, aerate or turn the grain while the outside temperature is low.

    The time required to kill insects depends on the grain temperature. For example:

    • A grain temperature of -5°C takes about 12 weeks to kill most insects.
    • A grain temperature of -10°C takes about eight weeks to kill most insects.
    • A grain temperature of -15°C takes about four weeks to kill most insects.
    • A grain temperature of -20°C takes about one week to kill most insects.


    Impact

    The physical impact of travelling through a pneumatic conveyor will control most mites and insects in your canola.

    Dockage

    Dockage is material that must be removed from grain by the use of approved cleaning equipment in order for grain to be eligible for the highest grade for which it may qualify (Canadian Grain Commission 1994). The amount of dockage in farm deliveries of canola to elevators in western Canada over the years prior to herbicide tolerant (HT) varieties has averaged 9% (Manitoba Agriculture, 1980). Current dockage levels in HT canola are much less than with conventional herbicides (O’Donovan et al. 2006). Dockage in canola consists mainly of wild oats, other weed seeds, volunteer cereal grain, broken seeds, broken pods and soil particles. This dockage normally has a moisture level 3% to 4% higher than that of the canola seed. Large amounts of broken seeds influence the rate of respiration because they provide a substrate for the growth of molds (Thomas, 1984). During binning of canola, the chaff concentrates towards the wall of the bin. Fines, or particles smaller than canola, increase the resistance to air flow, while chaff or particles larger than canola decrease the resistance. An equal proportion of fines and chaff in a canola load increases the resistance to air flow. Spreaders have not been found to distribute dockage and chaff more uniformly than spout fills (Jayas et al., 1987).

    Oil Content

    The oil fraction of canola seed absorbs less moisture than the starch and protein fractions; therefore the equilibrium moisture level for canola is much lower than that of wheat (Thomas, 1984). The amount of water that must be evaporated from canola to safeguard it from molding is therefore greater than with cereal grain. Modern canola varieties have higher oil content and thus the safe moisture and temperature levels for storage needs to be lower.

    Research is looking into the effect of higher oil content on stored canola under western Canadian conditions. A PAMI study shows that oil degradation after 2 months of storage is still within tolerance limits, but longer storage may result in significant oil degradation. (Gregg et al., 2012.)

    Based on the preliminary University of Manitoba research results on high oil canola, higher moisture content (12 and 14%) samples should be dried immediately if they need to be stored at higher temperatures (30 and 40ºC). For storing at lower temperatures (10 and 20ºC), canola seeds should be dried within 6 weeks to reduce deterioration.  Lower moisture content samples (8 and 10%) can be stored for more than 18 weeks at lower temperatures (10ºC, 20ºC), but can only be stored only for 2 and 4 weeks, respectively at 40ºC. Germination of the seeds decreases with increase in moisture content, storage temperature and duration of storage (Jayas; personal communication). 

    Australian researchers have published moisture isotherms for canola and related this to varying oil contents (Cassells et al., 2003).

    A practical guideline for the effect of oil content on safe storage moisture is:

    • for every 1% higher oil content, decrease the safe moisture by 0.1%.


    For example, if canola with 40% oil is safe at 8.5% moisture, then canola with 45% oil should be stored at 8% moisture. Although producers cannot easily measure oil content at harvest, if combined canola is larger in size than normal and cooler and wetter growing conditions during seed fill occurred, then it is very likely that the seed will have elevated oil content.

    Cultivar type

    Few storability studies have compared B. napus and B. rapa cultivars, or specialty oil types (high erucic, high oleic, low linolenic). Mills et al. (1978) studied the storage quality of 106 samples of B. napus and 71 of B. rapa. The samples were obtained from primary elevators across western Canada and assessed as sound, spoiled or heated. High fat acidity and conductivity levels, low pH, weathered seed surfaces, strong off-odors, and a brown seed interior on crushing, low germination levels, and high frequency ofAspergillusspp. storage molds were correlated and indicated deteriorating quality in both species of canola.

    Be Sure Your Canola is Export Ready :  Ensure bins and trucks are clean, free of de-registered varieties.

    Canola samples were considered high quality with (Mills and Sinha, 1980).:

    • seed with a sweet odor,
    • no visible mold,
    • less than 1% other seeds,
    • greater than 90% germination,
    • more than 97% yellow seeds after crushing,
    • conductivity of less than milliohms per centimetre, and
    • a fat acidity value of less than 30 mg KOH per 100 g of moisture-free seed


    Monitoring stored canola

    Monitor bins closely during the first six weeks and then continue to check stored canola regularly until delivery. Make sure stored canola cools to 15°C or lower throughout the bin. If stored canola temperatures plateau or start to rise while outside air cools through the winter, it can signal the start of spoilage. It only takes one small hot spot to start a chain reaction that can spoil a whole bin.

    Use properly anchored bin monitoring cables.

    These add to the cost of storage but make monitoring easier. One cable has a coverage diameter of 20 to 24 feet. Bins with a diameter greater than 24 feet will need at least three cables to adequately monitor grain temperature. More cables provide extra assurance because grain never conditions or dries consistently throughout the mass. Temperature fluctuations are normal based on erratic air flow patterns.

    Probes.

    Probing through doors or roof hatches may uncover hot spots near the bottom and top of the bin, but cannot show canola condition through the central core and all sides. Be careful and consider your own safety when climbing bins to probe grain. Reduce your risk of falling by using appropriate safety equipment such as a harness.

    How Type Of Storage Affects Safe Storage Of Canola

    Canola is very sensitive to heating in storage (Mills, 1976) and therefore requires better bin construction than that required for cereals to exclude moisture. The small size and free flowing characteristics of canola mean that high quality construction is necessary to prevent leakage. Roof and door openings, joints between structural components, and even bolt holes must be sealed to avoid losses. As heating and moisture migration problems tend to be more severe in larger storage structures, canola should be stored in the smallest bins available, without sacrificing convenience and efficient handling.

    Keep Your Canola Export Ready: Do not use malathion on canola before storing or in the empty bins where canola will be stored. If the bin was treated previously, do not store canola in bins within six months of treatment. Ensure bins and trucks are free of treated seed and animal protein such as blood meal and bone meal, and de-registered varieties.

    Bins

    Storage in wooden granaries does not facilitate control of seed leakage and also provides access for the entrance of moisture, insects and rodents. Steel granaries, on the other hand, require almost no maintenance and can be more easily sealed against pests and weather. Also, if conditioning of hot or damp grain is necessary, metal bins are best suited to the controlled movement of air through the grain mass. Regardless of the construction material used, storage structures must be as weatherproof as possible, yet still allow easy access to the bin for sampling and monitoring. The weather proofing process must include the floors of bins that are set on concrete. Concrete floors may resist the movement of water through the slab, but moisture can still enter the bin in the form of vapour. For this reason, it is important to place a vapour barrier, such as polyethylene, between the concrete and the gravel base during construction.

    Size

    Figure 3. Effect of Grain Depth on Static Pressure

    Research has shown that bin height does not affect the structural integrity of canola seed stored in tall bins.  The compression forces experienced by canola seed in tall bins (up to approximately 100 feet tall) are not detrimental to canola.  Some deformation of seed shape may be experienced, especially with increased moisture content, but seed coat rupture or oil exudation do not appear to be common.  Higher seed moisture content seems to correlate with increased compaction, but decreased germination was not evident. (Gregg et al., 2012)

    The aeration system and fan horsepower have to be adequate for the volume and configuration of canola storage. Increasing grain depth increases the static pressure and requires increased fan size to push air through the grain (Figure 3). To keep the fan requirements as low as possible, use large diameter, short bins with full floor perforations for natural air drying of canola.

    Saskatchewan Agriculture and Food extension shows the impact of differing grain bin sizes on fan requirements. Two grain bins of equal volume but different diameters require different aeration fan size because greater grain depths results in a higher static pressure (Table 4).

    Table 4. Effect Of Bin Diameter On Fan Requirements

    Also remember that the small size and round shape of canola seed leaves fewer air pockets relative to wheat and other larger grains, which adds to the aeration capacity requirement. For example, a 2,000-bushel hopper bottom bin may require only a 3 hp fan for wheat but will need a 5 hp fan to effectively condition canola.

     

    Grain Storage Bags

    A more recent type of storage being adopted is a harvest bag or silage bag made up of three-layer polyethylene membrane (235 microns thick) that is filled like a sausage in the field. They provide a nearly air-tight environment for the grains.

    Harvest bag adoption has been higher in Argentina and Australia, where farmers often do not have sufficient permanent storage capacity. In Argentina, more than 50% of the harvested grains were stored using silo bags in 2007 (Cardoso et al., 2008). 

    These harvest bag systems are cost competitive and provide flexible choice of storage location and surge capacity in years with high yield. Recent studies in Argentina and Australia indicate that canola can be successfully stored for a year with low moisture canola and careful bagging (Ochandio et al., 2010; Darby and Caddick, 2007).

    The harvest bags probably are best suited for short term storage of a few months. Shortcomings noted in the Australian report include:

    • easily torn or punctured membrane which leads to localized spoilage;
    • overall inadequate sealing (need to achieve air-tightness) under farm situations;
    • little protection against wildlife access;
    • localized condensation on the inside of plastic when grain is damp; and
    • insect disinfection method are not currently available.


    There may also be limitations under western Canada conditions such as below freezing temperatures during harvest or unloading that causes problems with the working properties of the plastic membrane.

    Accumulation of condensed water inside the grain bags is a common problem under Canadian climatic conditions. When compared to other storage systems, a high proportion of the bulk seed is held in the surface (peripheral) layer of the bag storage system. This peripheral layer undergoes large temperature and moisture changes during storage. More than 18% of the stored bulk in harvest bags has some quality changes (Darby and Caddick, 2007).

    In a demonstration project during the winter of 2009, 19 grain bags were monitored for temperature and quality changes in Saskatchewan. (Boyle, Stonehouse, Martinka, and Flaten, 2010).  Much of the canola crop was taken off and stored in November at moisture content between 10 and 13%.  The project found that the temperature decreased relatively quickly, likely due to the outside air temperatures between 2 to 16 degrees C. Seed temperatures also rose in the spring with rising air temperature. In two side-by-side bags with 12 and 14% moisture content, the higher moisture canola did not decrease in temperature to the same degree. Because the producers removed the canola from the bags for sale or drying when temperatures did not fall or began to rise, implications for long term storage could not be evaluated in this report.

    In research conducted at the University of Manitoba, canola with 3 moisture contents of 8, 10 and 14% were stored in grain bags from October 2010 to Aug 2011. Preliminary results showed germination rate of 14% m.c. canola seeds reduced to less than 50%, but there was no significant loss in germination rate of dry seeds (8 or 10% m.c.) throughout the 40 week storage period. There was no significant change in quality of dry seeds (8 or 10% m.c.) throughout the 32 week storage period.  In the second year of the study, 12% moisture content canola was stored in grain bags in September 2011. The canola maintained its No 1. Grade to the first unload date approximately 20 weeks after storage.  After 28 weeks in storage, the grade dropped to No. 2, and after 44 weeks, had dropped to Sample grade.  (Chelladurai, Jian, Jayas and White).

    With these preliminary results, the researchers concluded that, canola seeds can be stored at low moisture contents (8 or 10% m.c.) in silo bags for 7 months without significant quality deterioration. Wet canola seeds can only store for a short time without any quality deterioration.

    Grain bag storage tips:

    • Store only dry seed.
    • Store for short duration.
    • Monitor with temperature probes at least twice per week until temperatures stabilize.
    • Watch for rodent activity.
    • Clear snow to help prevent deer from walking on bags
    • Place in well-drained area.
    • Unload before frost goes out of ground in spring.
    • Place on grass to prevent stubble from poking holes in the bag.


    Importance of Conditioning for Canola

    The susceptibility of canola to heating justifies extra care when placing the grain into storage. Because bulk canola contains seed of varying ripeness and surface borne fungi from the field, it may undergo a sweating process before becoming dormant. Therefore the top hatch of the bin should be left open initially for several days during dry weather to allow heat and moisture to escape. The efficiency of conditioning operations will be enhanced by cleaning the seed prior to storage (Thomas, 1984).

    The term conditioning usually refers to those processes that involve the movement of air through seed to ensure safe storage over a period of time. Conditioning systems are used to cool or dry freshly harvested hot or moist seed, to avoid spoilage in storage. These systems also help to prevent moisture migration caused by temperature gradients which can occur in moist seed. Conditioning also reduces the effects of sweating, and is used even in areas where the seed usually can be harvested in a satisfactory state. Conditioning systems can extend the harvest season since canola can be removed from the field in a tough (>10.1% moisture) or damp (>12.5% moisture) condition; thus the harvest can be started earlier and continued later. The degree to which the harvest season can be extended will depend on the level of conditioning available. Conditioning also reduces field losses, as advancing the harvest means there will be less exposure of the canola to weather conditions that can affect the yield and grade. In addition, harvesting at a higher moisture level will reduce machine shatter losses and premature shattering of pods. The ability to condition canola also helps producers to avoid harvesting and selling of overly dry grain, thus minimizing economic losses, and to take advantage of good but short-lived market conditions prior to the main harvest (Thomas, 1984).

    Proper operation of conditioning systems, particularly natural-air systems, is dependent on the knowledge of the state of the seed. Monitoring of the seed condition is necessary to avoid danger of spoilage and to know when the operation is complete. A final sampling for both temperature and moisture content is advisable before long-term storage. The most critical factor in monitoring seed condition is an awareness of any changes that have occurred. Accurate monitoring, therefore, requires repeated sensing of conditions at specific locations. Permanent sensors in a bin add to the cost of a monitoring system, but ensure that measurements are always taken at the same place. Portable probes can be used effectively, but do not provide the same precision for repeated monitoring (Thomas, 1984).

    How Canola Compares To Other Grains

    Stored canola differs from stored wheat because, unlike wheat, adverse changes can occur very rapidly. Canola grain may go through a period of active respiration after binning, and if the heat and moisture is not quickly removed, mold growth and increased respiration soon occurs (Mills, 1989). Seeds can be conditioned to avoid spoilage in storage, to extend the harvest season, and to reduce field losses. Conditioning systems using aeration, natural-air drying or heated-air drying or a combination of these can ensure safe storage (Thomas, 1984). Going from cereal grains to canola during drying operations requires temperature readjustment because reduced airflows increase drying times and the possibility of unsafe temperature buildup (Canola Council of Canada, 1981). Under western Canadian conditions, canola can be stored readily for long periods of time at moisture levels of 8 to 9% if seed temperatures are below 20°C and insect and mite infestations are not present (Thomas, 1984).

    How Other Climates Compare To Western Canada

    In Kansas, it is recommended that canola be stored at a moisture content of 8 to 9% and temperatures of 10°C or less. For every 6°C or 1% moisture reduction below 25°C and 9% moisture, the storage life will double. Aeration fans are needed on any bin used to store canola, regardless of the storage time. Fully-perforated floors and aeration fans of 0.37 to 2.24 kilowatt are required to reduce temperature. It will take more than twice as long to move a cooling front through canola as grain, sorghum or wheat. Under Kansas conditions moulds and mites develop on canola if moisture content is above 9 and 8%, respectively. At 20°C, mites develop from egg to adult in about 14 days, however, if temperature is 4.5°C, development will take several months. High-temperature batch and continuous-flow dryers are frequently used. If the moisture content is above 17%, it is advantageous to dry the seeds in two passes. The first pass reduces moisture content to 12%, then the canola can be transferred to a bin for drying with natural-air. Too much moisture extracted at one pass can lead to shrivelling and cracking of the seed as well as limit the drying performance. Natural-air and low-temperature drying work well with canola if the moisture content is below 15% and the drying depth is less than 3 m.

    In North Dakota, heating and spoilage occurs at moisture levels of 9 to 10% and canola as low as 8.5% moisture should be examined for heating at regular intervals. If harvested at high moisture, natural-air drying or heated-air drying is recommended. To maintain seed quality, a maximum drying temperature of 43°C is recommended for commercial production.

    In Montana, canola is harvested at optimum storage moisture of 8 to 9% and stored in the smallest available bins with aeration. Fans are operated continuously until the temperature is near the average of the ambient air and long enough to be certain the cooling front moves completely through the bulk. Harvest temperatures may reach 27 to 32°C, therefore aeration should continue long enough to get the seed temperature below 21°C.

    In Maryland, seed will not store safely with more than 10% moisture and will not be considered acceptable by canola buyers. If seed is harvested with more than 10% moisture, it is likely to be discounted because of green seed. When marketed, seed quality is further discounted if seed moisture exceeds 9% moisture. It is essential that suitable drying facilities be available if seed moisture content at harvest exceeds 10%.

    In South Carolina, quality and handling regulations include a 1% discount for every 0.5% moisture above 9% with further financial discounts for the presence of heat damaged seeds over 0.1%, and musty, sour or weevil infested seeds.

    In Georgia, it is recommended that only clean seed be stored; seed moisture should not exceed 8 to 9% for storage of more than a few days; and aeration and air movement are used for short-term storage. Fans should be used in wet weather to prevent hot spots and mould development if seed contains more than 9% moisture. Periodically operate fans to remove any moisture that may have accumulated after drying to reduce the chance of mould growth. To control mite levels, bins should be thoroughly cleaned before seed is stored.

    In Western Europe, the climate is either temperate oceanic (United Kingdom, France, Denmark, western Germany) or temperate continental (Sweden, Poland, eastern Germany). Because of frequent wet weather, canola is normally harvested at a higher moisture level than in western Canada. To permit successful storage for a year or more requires drying from 20% moisture down to 7% moisture. A moisture level of 8% permits storage for only a few months before spoilage occurs. Aeration is adequate for seed lots with moisture contents of up to 10%, but seeds with greater than 12% moisture should be pre-cleaned and dried with hot-air in a continuous-flow dryer; mite infestations are a serious problem at higher seed moisture levels. According to Swedish guidelines, the seeds should be dried to a moisture content where they remain viable. Seed viability rapidly decreases to 40% from 100% when moisture levels increase from 9 to 12%.

    A study at Yorkshire, U.K. found the moisture level of the incoming canola seed varied considerably from about 8 up to 30% in extreme cases. A large proportion of the crop left the farm immediately for drying on contract by farmers or merchants using continuous-flow dryers. Safe drying temperature was up to 66°C to maintain the oil quality, but if the moisture level was above 17%, temperature was reduced to slightly above 50°C to safeguard germination. Very wet samples were often passed through the drier twice to reduce the likelihood of damage. Floor drying of rapeseed is frequently practiced in the U.K., with air blown through a 1.3 m deep layer of seeds via mesh-covered ducts at the bottom of the bulk.

    Types of Conditioning Systems

    Conditioning systems can be divided on the basis of both the purpose and the state of the air used in the operation. Natural-air systems use the surrounding or ambient air to condition the grain, whereas, heated-air conditioning systems use energy to heat the ambient air. Heated-air conditioning systems have a higher capacity for drying canola because of the increased drying ability of heated, low-humidity air and the higher airflow rates usually used. Conditioning systems are usually separated into aeration, natural-air drying, and heated-air drying categories; combinations of these systems, involving two or more of these operations, are also used (Thomas, 1984).

    Aeration vs Natural Air Drying

    Aeration = cooling/conditioning

    • Airflow rate approximately 0.1 to 0.2 cfm/bu
    • If air is cooler than grain, grain will cool.
    • At 0.1 cfm/bu, about 200 hours of fan operation will be required to equalize the temperature in the bin.

    Natural air drying (near ambient drying) = reducing the moisture in the grain.

    • Airflow rate approximately 1 to 2 cfm/bu
    • If air has capacity to dry (depending on air temperature and relative humidity and grain moisture content), grain will dry.
    • Drying is highly dependent on ambient temperature and relative humidity conditions.


    Aeration Systems

    Aeration systems are used to preserve seeds by cooling and by preventing moisture migration. They are used during seed storage, between harvesting and drying operations and after heated-air drying.

    Operation of Aeration Systems

    The purpose of an aeration system is to produce the lowest practical temperature and the least temperature variation within the stored seeds. The amount of air required to change the temperature of the seed will produce very little change in moisture level. At moisture contents above 11%, aeration should not be used alone unless seed temperatures are near or below 0°C. Management of aeration systems differs in fall, winter, spring, and summer seasons (Friesen and Huminicki, 1986).

    The airflow rates for aeration of canola are normally 1-2 L per second per M3. With an airflow rate of 1 L per second per M3 about 150-200 hours of fan operation are needed to change the temperature throughout the bin; at 2 L per second per M3 this time is halved (Friesen and Huminicki, 1986).

    Tip:  Aeration fans should be started as soon as the canola covers the floor of the bin, so that immediate cooling can take place. Fans must be operated continuously until the temperature of the canola is near the average outside temperature.

     The operation of aeration equipment during extended periods of high relative humidities (over 80%) may promote mold growth, even in dry canola. However, continuous aeration through one or two days of high relative humidity will not damage the canola, as long as an equal time of dry weather follows. Since aeration is essentially a cooling procedure, the temperature of the air is more important than the relative humidity.

    Tip: 

    • When the outside temperature has dropped below the temperature of the stored canola by 5 to 10°C, the canola should be cooled again.
    • No conditioning operation is complete until the temperature and moisture level of the entire bulk have reached the desired level.
    • After the bulk has reached the desired storage temperature, the bin should be checked periodically for evidence of heating or moisture migration.


    Aeration can be accomplished by moving air upward or downward through the grain bulk (Figure 4).

    Figure 4.

    Figure 4. Air movement patterns in upward and downward aeration systems
    There are advantages and disadvantages to each direction, but in most situations upward air movement is preferred. Upward air movement permits the aeration progress to be easily determined by checking the canola temperature at the top of the bin. Also, with an upward air flow, the fan can be started prior to filling and air leaving the duct will help to keep the perforations clear of fines as filling progresses. The disadvantage of moving air upward is the potential for condensation to form on the underside of the roof when aerating warm seed in cold weather. Moving air downwards and exhausting it at the bottom minimizes condensation. However, in downward air movement, the canola at the bottom is the last to cool and the hardest to check to determine when aeration is complete. A further disadvantage of downward movement is that when warm seed is added to the bin, the heat from the added seed is drawn through the previously cooled seed and warms it up again. When aerating grain in summer, downward movement will draw the hot-air from under the roof down through the rest of the seed (Friesen and Huminicki, 1986), another disadvantage.

    Under hot, humid harvesting conditions, such as often occur during late July and August in southwest Ontario, aeration can result in a greater potential for condensation within the bin. Moisture condensed on the inner bin roof will then drip onto the bulk surface favoring moldy crust development and insect pest populations. In this case, cross-ventilation to remove warm air rising from the bulk surface is effective before condensation occurs. Delaying aeration until air temperatures have moderated will avoid the problem (Mills, 1990).

    Aeration systems

    The specific requirements of aeration systems for canola are determined by the susceptibility of the seed to spoilage and its physical characteristics. The small size of both canola seeds and the void spaces around the seeds increases the resistance of this crop to airflow. Aeration fans must operate at static pressures two to three times greater in canola than in cereals, consequently systems designed for cereals may not produce adequate airflow rates through canola; and the risk of spoilage to the seed may be substantial. In B. napus varieties of canola, aeration fans typically operate at static pressures of 200 pascals at a seed depth of 3.4 m, and 500 pascals at 8.3 m depth. The smaller seeds in the B. rapa varieties can increase these static pressures to 300 pascals and 750 pascals for the 3.4 m and 7.3 m depths, respectively (Thomas, 1984).

    Many duct and perforated floor arrangements are available for use with aeration systems (Friesen and Huminicki, 1986). Given the sensitivity of canola and the difficulty in forcing air through it, a large perforated floor area is required (Thomas, 1984). Perforations must be small enough that seeds cannot enter the air passages. A 6-m deep bin requires a minimum of at least 15% perforated floor area; a 10-m deep bin should have at least 25% perforation to avoid excessive air velocities (Friesen and Huminicki, 1986). A completely perforated floor usually produces uniform airflow throughout the bulk and reduces the chance of unventilated spoilage pockets developing (Mills, 1990). Uniform air distribution is more difficult to achieve in flat (horizontal) grain storages than in cylindrical bins because flat storages usually have less uniform grain depths; to help offset the associated air-distribution problems, use higher airflow rates of 2 to 3 L per second per m3. Foreign material in the canola bulk may reduce the overall static pressure requirements, but increase the possibility of spoilage. Furthermore, the concentration of dockage at the centre and outer edges of the bin creates uneven resistance to airflow and hinders the effectiveness of conditioning operations. The uniform distribution of fine and coarse material is advantageous when canola is being aerated (Thomas, 1984).

    Natural Air Drying

    Moisture can be removed from stored canola by passing outside air at high flow rates through the bulk with the only heat coming from the fan and motor. Grain in a ventilated bin begins to dry where the air enters the bulk, usually at the bottom of the bin. A drying front develops and moves slowly upward through the bulk. Below the drying front the grain is at the temperature of the incoming air and at a moisture level in equilibrium with the incoming air. Incoming air at 70% relative humidity, for example, will result in moisture levels of between 8 to 9% for canola seed (Table 5).

    Table 5. Relationship between Seed Moisture Level and Relative Humidity of Ambient Air for Drying of Canola
    Relative humidity (%) 50 57 65 72 77 82 86 88
    Moisture level (%) 6 6.6 7.4 8.2 10.0 11.2 12.8 13.9


    Natural air drying using aeration alone can remove one or two percentage points of moisture, but only if outside air has “capacity to dry.” Air’s capacity to dry depends on its temperature and relative humidity (RH) (Table 6). For example, if air has 50% relative humidity and is 5 degrees C, and it is passed over canola for a length of time, the canola will eventually equilibrate to 8.1% (regardless of whether it started at 10% or 6%). Air with a higher RH may be capable of cooling the grain but don’t expect much drying capacity. In winter, as temperatures drop, the capacity to dry canola using aeration alone is minimal unless RH is very low.

    Table 6. Equilibrium Moisture Content for Canola/Rapeseed
    Temp °C 35 40 45 50 55 60 65 70 75 80 85
    -2 6.7 7.5 8.2 8.9 9.7 10.5 11.3 12.2 13.2 14.3 15.7
    2 6.4 7.0 7.7 8.4 9.1 9.9 10.7 11.6 12.5 13.6 14.9
    5 6.1 6.8 7.4 8.1 8.8 9.5 10.3 11.1 12.0 13.1 14.3
    8 5.9 6.5 7.1 7.8 8.5 9.2 9.9 10.7 11.6 12.6 13.8
    10 5.7 6.3 7.0 7.6 8.3 8.9 9.7 10.5 11.3 12.3 13.5
    13 5.5 6.1 6.7 7.3 8.0 8.6 9.4 10.1 11.0 11.9 13.1
    15 5.4 6.0 6.6 7.2 7.8 8.5 9.2 9.9 10.7 11.7 12.8
    18 5.2 5.8 6.4 7.0 7.6 8.2 8.9 9.6 10.4 11.3 12.4
    22 5.0 5.6 6.1 6.7 7.3 7.9 8.5 9.3 10.0 10.9 12.0
    26 4.8 5.4 5.9 6.5 7.0 7.6 8.2 8.9 9.7 10.5 11.6
    28 4.8 5.3 5.8 6.3 6.9 7.5 8.1 8.8 9.5 10.4 11.4

    Source:  PAMI.

    The grain above the drying front will remain at a moisture level within about 1% of its initial storage condition. The rate of movement of the drying front is mainly affected by the airflow rate per unit mass of seed. To dry the entire stored crop in the least possible time requires a uniform air pattern throughout the bulk. The airflow pattern in a bin equipped with a completely perforated floor and a leveled grain surface is uniform unless a centre core of densely packed grain and dockage has formed under the filling spout (Mills, 1990). The required airflow rate for unheated-air drying depends on the type of grain, when the grain is harvested, its initial moisture level, and the outdoor air conditions (Friesen and Huminicki, 1986). Typical airflow rates for unheated-air drying are in the range of 5 to 25 L per second per m3 (Thomas, 1984). For the lowest equipment and operating costs, the lowest recommended airflow is used. Minimum airflow rates for in-bin drying are chosen so that the crop dries just before it undergoes unacceptable spoilage (Mills, 1990). Theoretical minimum airflow rates for natural-air drying of canola in the area of Winnipeg, Manitoba without loss in quality are given in Table 7 (Muir and Sinha, 1986).

    Table 7. Theoretical Airflow Rates for Natural-air Drying of Canola
    Date Predicted Minimum Air Flow Rate Requirements for Natural-air Drying in the Winnipeg Area*
    Initial Moisture Level (%)
    11 13 15
    Air Flow Rate, (litres per second per m3)
    August 15 11 15 28
    September 1 13 20 23
    September 15 17 20 24

    * Predictions are based on the top layer dried to 10.0% moisture within 15 - 20 days for the median of 17 years of recorded meteorological data.

    A more comprehensive simulation model has been developed for in-bin drying of canola under Saskatoon, Saskatchewan weather conditions. (Arinze et al. (1993).

    The drying of canola by near-ambient air is currently favored in western Canada rather than the use of hot-air. Near-ambient drying is preferred because there is a saving of energy, a smaller initial investment in equipment, and an improvement in the quality of the dried product compared to that dried with hot-air systems (Jayas and Sokhansanj, 1985).

    Operation of Natural-Air Drying Systems

    Tip:

    • The fans should be started as soon as the canola covers the perforated areas of the bin floor.
    • Operated continuously in the fall until either the crop temperature is reduced to 0°C or the crop is dry.
    • In spring, if drying was not completed the previous fall and no spoilage has occurred, drying is continued when the air temperature rises above 0°C.


    Even under humid or rainy conditions the fan is operated continuously to ensure that the main drying front will continue moving through the bulk despite the risk of rewetting the bottom slightly. As long as the fan operated for a few days after the humid period, the moisture will redistribute through the bulk and will not cause spoilage. Rewetting can be an economic benefit if the canola at the bottom has dried below the maximum allowed selling moisture level. Although it improves the storage quality, any drying below this regulatory value reduces the saleable mass, and thus the monetary value of the bulk (Mills, 1990).

    Natural-Air systems

    The proper design of natural-air drying systems is important because of the need to dry the bulk quickly enough to prevent spoilage. High airflow rates are used which result in high static pressures. The airflow resistance of a grain mass is directly related to the depth, so reducing the grain depth is one way of bringing static pressures into an acceptable range. Fans drying B. napus varieties of canola operate at typical static pressures of 1,000 pascals at a depth of 3.0 m, and 2,000 pascals, at a depth of 4.3 m. Using comparable fans to condition B. rapa varieties, depths are restricted to 2.6 m and 3.6 m, respectively (Thomas, 1984).

    Bulk density and porosity are major considerations in designing near-ambient drying and aeration systems because these physical properties affect the resistance to airflow of the stored mass (Bern and Charity, 1975). The bulk density and porosity of B. rapa (cultivar Tobin) and B. napus (cultivar Westar) were studied using loose and dense filling methods (dense fill simulates packing when seed falls from a significant height). (Jayas et al. (1989). The bulk density of Westar was 3.6% lower than that of Tobin canola. Dense fill resulted in bulk densities about 12% higher and porosities about 14% lower than the respective properties for loose fill.

    High flow rates require an effective design for the air distribution system. The ducts delivering air to the bin, together with any transitions along this network, must have sufficient area for the required airflow. Fully perforated floors for natural-air drying systems are often recommended, especially for canola (Friesen and Huminicki, 1986). Natural air drying can lower canola moisture content up to 2% over 2 months after harvest (Sinha et al., 1981).

    Grain Dryers – heated air drying

    Heated-air drying is used when aeration or natural-air drying fails to adequately condition canola. This may occur when ambient (outdoor) weather conditions are wet and cold or when canola is very damp following harvest. Rapid drying is essential to prevent spoilage. Other circumstances for heated-air drying are the need for an early harvest and rapid drying to meet best markets or contractual obligations, and to reduce the risks at harvest to producers having lower field-harvesting capacities. Hot-air drying differs from natural-air drying in that heated-air will absorb considerably more moisture from the grain, and the warming of canola forces moisture out much more rapidly (Thomas, 1984). Bin, batch, and continuous heated-air dryers may be used to dry canola. Multistage drying, using grain dryers and high-capacity aeration systems are also used effectively (Friesen, 1981; Thomas, 1984). An efficient system of augers, hoppers and other handling equipment is necessary when heated-air drying systems are used to ensure a continuous flow of grain from the field to the bin (Friesen, 1981).

    Heated Air Drying Temperatures

    The maximum air plenum temperature for drying canola depends on seed moisture level, seed viability temperature, expected storage period, type of dryer used, and other factors. Generally, a wetter seed requires a longer drying process at a lower drying temperature.

    Seed viability is adversely affected when drying temperature is too high; damage is more likely to occur when the seeds are dry or nearly dry. To prevent seed damage, it is important that maximum seed temperature does not exceed the maximum allowable temperature for the type of seed and its intended purpose.

    Tip:

    • Canola destined for seeding purposes should be dried at less than 45 to 50°C.
    • For oil extraction, seeds can be dried at up to 82°C.
    • Lower temperatures are used when canola is damp (over 12.5 % moisture) or when it is to be stored for over six months.


    Overdrying causes cracking of the seed coats; damaged seeds undergo a marked rise in the level of free fatty acids causing a reduction in oil quality. Seeds dried to moisture levels below 6% are very fragile and subject to mechanical damage during handling, whereas seed above 7% moisture will not suffer cracking (Nash, 1978). Additionally, visible cracks and blackening were observed when seeds were dried at an elevated temperature of 250°C. (Pathak et al. (1991). Canola drying temperatures are shown in Table 8.

    Table 8. Safe Drying Temperatures for Canola
    Grain Condition
    (% moisture)
    Maximum Temperature of Drying Air °C
    Seed Grain Commercial Grain
    Mixed During Drying Unmixed
    Tough (10%) 49 82 71
    Damp (12.5%) 43 71 60


    A non-recirculating batch dryer or a dryer which does not mix or circulate the seed requires a lower operating temperature as seeds next to the hot-air plenum will warm to near the hot-air temperature (Friesen, 1981; Thomas, 1984). For these dryers, temperatures 5 - 10°C lower than those listed for commercial use are advisable.

    Heated Air Drying Considerations

    Drying decisions will depend upon the maximum periods available for drying before mold growth occurs. The drying rate for canola is less than that for cereals because of the reduced airflow through the smaller, more densely packed seed. As canola offers more resistance to airflow than cereal grains, the fan on a dryer operating at the same speed used for grain will produce a higher static pressure but considerably less airflow. This causes the temperature of the hot-air plenum to rise unless the fuel flow is reduced. Another consideration in drying canola is leakage. Grain dryers are designed mainly for wheat and corn (Zea mays L.) and must be adjusted and checked for canola losses through leakage or being blown from the drying chamber by the higher static pressure. Screens and floors of dryers more than 10 years old should be checked for rust perforation to prevent canola leakage (Harner, 1989). Green weed seeds and canola stems and pods may interfere with the passage of canola through the dryer and at high drying temperatures stationary canola may catch fire (Thomas, 1984). Canola seeds may also ignite when they are passed by the burner. Fire risk when drying canola may be reduced by cleaning the seed to remove light or fine material before drying, removing accumulations of debris from the walls and other areas of the dryer, using wind deflectors to prevent drawing airborne material through the burner, avoiding overdrying the seed, and putting canola through the dryer on warm sunny days without starting the burner (Mills, 1989).

    J. T. Mills - Agriculture and Agri-Food Canada, Winnipeg, Canada January - 1996
    Revised by M. Hartman – Alberta Agriculture and Rural Development, 2011


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