AGRICULTURE
REPORT - Pressing Oil from Seeds
By Gary Garriott
This is Steve Ember with the VOA Special English
Agriculture Report.
From the beginning of human history, people have used
oils from seeds and nuts. Most of the time these oils are used as food,
especially in cooking. But sometimes they have other uses. For example,
oils are found in paint and in cleaning products, like soap.
Oil is separated from seeds by using pressure. A machine
called a press is often used. Sometimes it is surprising to learn how
much oil the seeds contain. These common seeds all contain at least
fifty-percent oil: olives, groundnuts（落花生）,
sesame, cotton and sunflower（向日葵）.
The soybean is an important seed around the world,
but it is only twenty percent oil. So chemicals are needed to release
oil from soybeans.
The first step in pressing the oil from seeds is to
crush the seeds between two stones. A cloth container or bag is filled
with the crushed seeds. Then the bag is hung up. Some of the oil will
flow out of the bag and can be collected. But some oil will remain in
the crushed seeds inside the bag. The easiest way to get the rest of
the oil out is to place heavy rocks on the crushed material.
Another method is to place several cloth bags on top
of each other in a box. Then a long wooden stick is used to slowly push
a heavy cover down on the bags. Great pressure is produced in this way.
Much greater pressure can be produced by using a machine, a hydraulic
jack（水压千斤顶）. The greater the pressure, the more oil will be produced.
Oil can also be collected with small, hand-operated
machines. Small presses are important in areas where electricity or
gasoline cannot be used. They are also a good way to test if a local
market for oil exists.
Small batch presses can be made of local materials.
Their cost is low. They are not difficult to operate. And they are easy
to repair. The small presses produce good quality oil. But the work
is hard. And getting all the oil from the seeds can be difficult.
A system can be set up to press together an amount
of seeds at different times of the day. But if there is a large supply
of seeds, then large, powered presses that can operate all day are needed.
You can get more information about collecting oil
from seeds from the group VITA, Volunteers in Technical Assistance.
VITA is on the Internet at v-i-t-a dot o-r-g.
This VOA Special English Agriculture Report was written
by Gary Garriott. This is Steve Ember.
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