Small-scale oilseed processing
Practical Action
Motor driven ghanis are now common in South Asia where they are used for mustard and rape
seed oil extraction. Their capacity is approximately 12 to 15 kg per charge. Each charge takes
around 75 minutes to process, so several charges can be processed in a day.
The equipment can be made locally and the running costs can be low. The oil yield is relatively
high at around 60% although production is slow.
Small-scale manual presses have been promoted by a
number of organisations. As these machines do not
require any power source their running costs are
minimal.
Types of manual press include:
Spindle press
Bridge press, also known as a screw press
Ram press
Hydraulic press
Manually powered spindle presses are usually small
table mounted devices with a capacity of around 2 to
5 kg per hour.
The bridge press comprises of a cylinder that
contains the seed which is compressed by rotating a
screw down onto the seed. The screw is held in place
by a frame that bridges over the seed container. As
the seed is compressed the oil drains through holes
Figure 4: A manual screw press
Photo credit Practical Action / Paul
Harris
in the cylinder onto a collection tray. The process is
relatively slow as the cylinder needs to be filled,
compressed and then the remaining cake needs to be removed.
Ram presses use a lever mechanism to produce high pressures on a piston that forces the oil out
of the seed. Manual ram presses can be tend to be hard work.
Hydraulic presses use a hydraulic pump to exert a high pressure on the seed. Hydraulic jacks
from cars and trucks can be used. The process is similar to a screw press, in that the seed has to
be loaded into a cylinder and then pressed to extract the oil, which runs onto a collection tray.
Once the seed has been pressed the remaining cake needs to be removed. Capacities are from
around 1 kg per press.
In India in particular a number of efficient
small or "baby" motorised expellers are
available with a capacity of up to 100
kg/hr. A typical machine has a central
cylinder or cage fitted with eight separate
sections or "worms". This flexible system
allows single or double-reverse use and
spreads wear more evenly along the screw.
When the screw becomes worn only
individual sections require repair, thus
reducing maintenance costs. As the seed
passes through the expeller the oil is
squeezed out, exits through the perforated
cage and is collected in a trough under the
machine. The solid residue, oil cake, exits
from the end of the expeller shaft where it
Figure 5: Tinytech oil expeller in operation in
Zimbabwe.
Photo credit: Practical Action / Keith Machell
is bagged.
Filtration
The crude expelled oil contains solid particles. These can be removed by allowing the oil to stand
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