Preparation is the first step in the process of extracting oil from oilseeds.
Once harvested, oilseeds are stored for some time before transported to the extraction facility. Inorganic and organic impurities accumulated during harvesting, storing and transport must be removed before the extraction process can begin. These include contaminants like leaves and stems, shells, dirt, stones, cloth, woodchips, metal, glass. They must also be sorted to remove imperfect or diseased oilseeds, pests before extraction.
Oilseed preparation is a critical step in the extraction process and when oilseeds are not prepared properly, it can result in
- Poor yield efficiency
- Poor oil quality
- Discoloured oil from the presence of flora and pests
- Malodorous oil
- Increased sediment
- Poor quality of extraction by-products
- Damage to parts from inorganic debris like stones, glass or metal
- Blockages in the feeding inlet
- Shorter life span of parts and the machine
- Production accidents
Efficient preparation also ensures the production of oil cake in different grades and protein levels to meet individual market needs or requirements.
There are 5 key steps in the oilseed preparation process.
In this step, all the foreign materials are carefully removed from the oilseeds and imperfect and diseased oilseeds are separated. Depending on the type of oilseeds a combination of the following equipment is used to select and clean:
- Vibrating sieve for screening,
- A destoner to separate seeds from stones
- Magnets to remove metal impurities
Oilseeds with casings like sunflower, peanuts, cottonseed must be dehulled before the extraction process can begin. Shells and hulls absorb the oil and reduce oil yield significantly. Moreover, colour compounds and waxes in the hulls degrade the quality of the extracted oil. The process of separating the seed from the casing is known as dehulling or decorticating. Dehulling can also be called shelling or decorticating. With a good quality dehuller, you are assured of efficient production and minimal wear on the expeller.
While smaller oilseeds like rapeseed do not need to be cracked or flaked, oilseeds like soybean, sunflower, cotton seed are usually cracked to facilitate hull removal and size reduction.
Cooking or conditioning of the seed ensures an efficient oil output. Conditioning is a key aspect of the extraction process, and the quality of the conditioning determines the quality of the pressing. It imparts elasticity to the seeds.
Oilseeds are also flaked before the solvent extraction process for high and efficient oil output. Flaking ruptures the cellular structure of the seed and increases it surface area so there is increased contact between the seed and solvent during the extraction process. Flake thickness ranges from 0.25-0.37 mm in size. It is advisable to extract oil within 24 hours of flaking to minimise meal and quality degradation.
Effective preparation is 70% of the job done when it comes to oil extraction. It allows you to improve yield, generate quality oil and meal products and increase the longevity of your equipment.
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