Recommendations for the storage and conditioning of rapeseed in a metal silo.
Rapeseed is an oilseed that, due to its seed size, offers different challenges at harvest and post-harvest: handling, movement of grain inside the silo, aeration and drying .
The original state of the product is the factor that most affects the preservation of rapeseed during storage.
During the “transpiration” stage, which takes place during the first 6 weeks of storage, the high respiration rate of the seeds produces hot and humid conditions that favor the development of fungi, which produce more heat and humidity, so constant monitoring is necessary. This effect can be minimized by cold, dry store of seeds.
FACTORS AFFECTING RAPESEED STORAGE
Humidity, temperature, and storage time
Rape seeds are more prone to deterioration during storage than cereals, so they must be stored at lower humidity level to prevent the development of fungi and ensure proper conservation.
For a “safe” storage, the relative humidity of the storage space must be 70% or less. Storing grains above this safe humidity level may create optimal conditions for fungal development. Therefore, if the rape is harvested wet, drying will be very important to insure safe storage conditions.
Temperature also affects rapeseed storage. If the silo is filled with hot seeds, since the rape is harvested in summer, and there is no aeration, the seeds will remain at high temperatures throughout the storage period due to the insulating characteristics of the grain.
The combination of temperature and humidity of the seed determines whether the storage condition is safe or not.
Fungi, insects and mites
Field-harvested seeds come with fungal spores. It is not possible to eliminate these spores, but it is possible to create conditions that are unfavorable to their development.
Most fungi achieve maximum growth at temperatures between 25º and 28º. The lower the temperature, the less the fungi will be able to grow.
Insects can be found in stored canola or rapeseed, but their ability to establish and infest the silage during storage is highly variable.
In general, whole seeds are more resistant than damaged seeds and only a few insects have been reported to be able to tolerate the high oil levels of canola or rapeseeds.
Mites feed on the surface and inside of the rapeseed, affecting the weight (fat loss) and the quality of the product. Their presence is associated with the presence of insects and fungi in the bulk, since they require high humidity conditions in the grain to survive.
POST-HARVEST HANDLING OF CANOLA OR RAPESEED AND ITS EFFECTS ON QUALITY
The main processes involved in the post-harvest handling of rapeseed are storage, handling and conditioning. If all these processes adequately performed, the highest quality of rapeseed will be maintained.
It is very important to store the seed:
- In good quality facilities to prevent the entry of humidity, since the rapeseed is very susceptible to heating and fungal development.
- In well-constructed facilities to prevent product loss.
- In small silos to prevent moisture migration.
In concrete-based silos it is important to check that there are no cracks through which moisture can enter.
Because rape has a high respiration period when the silo is filled, it is recommended to equip the silo with ventilation and temperature control systems.
The particle size of the product poses a real challenge in terms of product transport and storage. This consideration is especially important if losses are to be reduced, whether due to product loss or grain breakage.
Due to the small size of the seed, it is necessary to ensure that the grain handling machinery does not have openings through which the product can escape.
The augers and threads must be used at maximum capacity to prevent grain from seeping between the thread and the pipe.
Rapeseed has a lower density than wheat, so a 100 T wheat-based silo can store up to 87 T of rapeseed (Specific rape weight: 620 kg/m3).
Through drying and aeration the grain is kept in safe storage conditions.
Early harvest and subsequent plant conditioning may contribute to reduce losses in quality and quantity (yield) since the seed remains exposed to inclement weather for less time.
An exhaustive sampling of the silo is advisable to determine the temperature and humidity conditions of the total mass of grains for their correct, final storage.
For proper conservation of rapeseed, it is important to monitor the moisture condition of the seed, to see when the storage operation is concluded. For proper temperature monitoring, the installation of thermometry systems is recommended as they ensure its quality and allow us to know the development of temperature over time.
The conditioning systems are divided into:
- Aeration systems
- Drying systems with natural air or low temperature
- High temperature drying systems
Aeration systems control the moisture of stored seed and are used to cool recently harvested seeds and to maintain and standardise seed temperature during long-term storage. These systems, when properly sized, can also be used to temporarily keep grain moist prior to drying or to cool and finish drying hot grain coming out of the high temperature dryer.
Aeration systems designed for rapeseed must take into account the particular susceptibility of the seed to damage by self-heating and the physical characteristics of the seed.
It is important to highlight that the grain size of the rapeseed requires good aeration design for two reasons:
- The grids through which the ventilation air is introduced into the silo must have holes that are small enough to prevent the product from escaping.
- The small intergranular space greatly increases the resistance to the passage of air through the product, which increases the pressure drop of the air flow. This results in the need to use high pressure fans on many occasions.
Natural air/low temperature (AN / BT) systems are characterised by drying in silo with natural air, or air heated up to 7° C above ambient temperature.
The performance of these systems is highly influenced by climatic conditions since, if they are very dry, the drying will be completed in a short time, but the lower layers will be overdried and, if they are very humid, the drying will take a long time to reach the upper layer of the bulk. In this case, and to gain independence from the climatic conditions, supplementary heat can be used.
High temperature drying allows harvest humidity to be lowered to safe storage values much faster than natural air or low temperature drying systems. This occurs because hot air has a much greater capacity to extract water than natural air, and also because high temperature dryers use air flow rates much higher than that of other systems, although they should not exceed 90ºC (unlike cereals that easily exceed 110ºC).
Both, the buffer silos before drying and the tempering silos after drying must be equipped with fans and roof extractors.