Small-scale oilseed processing
Practical Action
Equipment required
The equipment needed to set up a small or medium scale oil extraction enterprise falls into three
main categories:
pre-extraction equipment; dehullers or decorticators, seed/kernel crackers, roasters, grinding
mills.
extraction equipment; ghani, manual bridge press or ram press, expellers
equipment for basic refining of the oil; filters, settling tanks for caustic soda to treat free
fatty acids FFA (do not use aluminium tanks).
packaging equipment
The specific equipment required will depend on the particular crop being processed, the final oil
quality required and the scale of operation.
Shelling or dehulling
Most oil-bearing seeds need to be
separated from their outer husk or
shell. This is referred to as
shelling, hulling or decorticating.
Shelling increases the oil
extraction efficiency and reduces
wear in the expeller as the husks
are abrasive. In general some 10%
of husk is added back prior to
expelling as the fibre allows the
machine to grip or bite on the
material.
A wide range of manual and
mechanical decorticators are
available.
Figure 3 : Decortication (removal/winnowing of husks)
machine for sunflower seeds. The decortication
machine is used in conjunction with Tinytech oil mills.
Photo credit: Kieth Machell / Practical Action
After decortication the shell may
have to be separated from the kernels by winnowing. At small scale this can be done by throwing
the material into the air and allowing the air to blow away the husk. At larger scale mechanical
winnowers and seed cleaners are available.
Milling is carried out to reduce the size of particles and improve the efficiencies of extracting oil.
Heating or conditioning
Pre-heating the seeds prior to expelling improves the release of the oil by breaking the cell walls
and by thinning the oil. The most basic method of heating is spreading the seed on a black
plastic sheet exposed to the heat of the sun for 15 minutes. Stoves can be used either with a
pan for 5 minutes or with a double-boiler for 15 minutes. There is a likelihood that the seed will
burn while using a pan which is not the case with a double-boiler. A double-boiler is an
arrangement in which one pan is placed inside a larger pan without touching the bottom or
sides. Water is placed at the bottom of the larger pan and is heated to produce steam that heats
the seed in a more controlled manner preventing the seed from burning. Special kettles can be
made, for example from an old oil drum, or a commercially available kettle that is specifically
designed for this task can be purchased. Pre-heating is often done with the kettle mounted
above the expeller.
Expelling
A wide range of makes and sizes of expellers are available. A ghani is a pestle and mortar that is
traditionally animal powered. Its capacity is approximately 40 kg a day although this will vary
depending on the size, strength and number of animals used. Animals need to be replaced after
3 or 4 hours work as they tire.
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