Oil is extracted from a number of fruits, nuts and seeds (Table 1) for use in cooking and
soapmaking1 or as an ingredient in other foods such as baked or fried goods. Oil is a valuable
product with universal demand, and the possible income from oil extraction is therefore often
enough to justify the relatively high cost of setting up and running a small scale oil milling
business.
-Raw material preparationOilseeds and nuts should be properly dried before
storage, and cleaned to remove remove sand, dust,
leaves and other contaminants. Fruits should be
harvested when fully ripe, cleaned and handled carefully
to reduce bruising and splitting. All raw materials
should be sorted to remove stones etc. and especially
mouldy nuts, which can cause aflatoxin poisoning.
When storage is necessary, this should be in
weatherproof, ventilated rooms which are protected
against birds, insects and rodents. Some raw materials
(for example groundnuts, sunflower seeds) need
dehusking (or decorticating). Small manual machines
are available to give higher production rates than
manual dehusking (Figure 1).
Figure 1: A Decorticating Machine
Dehusking is important to give high yields of oil andreduce the bulk of material to be processed` but in
groundnut oil extraction about 10% by weight of husk
should be added back to the nuts to allow oil to escape
more freely from the press. Coconut is dehusked and
split by skilled operators as this is faster than the
available small-scale machines. Most nuts need grinding
before oil extraction to increase the yield of oil. Small
mills are available for grinding copra, palm kernels and
groundnuts.
Figure 2: A Seed Scorcher
Some seeds (e.g. groundnuts) are conditioned by
heating to 80-90oC using a seed scorcher (Figure 2), and
all oil-bearing materials need to have the correct
moisture content to maximise the oil yield. Other
oilseeds and nuts are usually processed cold provided
that their moisture content is below about 7%.
Methods of extraction
There are basically three methods of removing oil from the raw materials: solvent extraction,
wet processing or dry processing. Solvent extraction is not suitable for small-scale processing
because of high capital and operating costs, the risk of fire and explosions from solvents and
the complexity of the process. Equipment for wet or dry processing is available at different
scales of operation from household to industrial scale. Traditional methods of extraction are
described below, followed by higher output manual machines and mechanised extraction.
Traditional methods
Oil is extracted from fresh coconut, olives, palm fruit shea nut etc. by separating the flesh and
boiling it in water. Salt is added to break the emulsion and the oil is skimmed from the surface.
In palm oil processing the fruit is first heated in a ‘digester’.
Methods of extraction
There are basically three methods of removing oil from the raw materials: solvent extraction,
wet processing or dry processing. Solvent extraction is not suitable for small-scale processing
because of high capital and operating costs, the risk of fire and explosions from solvents and
the complexity of the process. Equipment for wet or dry processing is available at different
scales of operation from household to industrial scale. Traditional methods of extraction are
described below, followed by higher output manual machines and mechanised extraction.
Traditional methods
Oil is extracted from fresh coconut, olives, palm fruit shea nut etc. by separating the flesh and
boiling it in water. Salt is added to break the emulsion and the oil is skimmed from the surface.
In palm oil processing the fruit is first heated in a ‘digester’.
Manual methods
Oil can be extracted by pressing softer
oilseeds and nuts, such as groundnuts and
shea nuts, whereas harder, more fibrous
materials such as copra and sunflower
seed are processed using ghanis. Pulped
or ground material is loaded into a manual
or hydraulic press to squeeze out the oilwater
emulsion. This is more efficient at
removing oil than traditional hand
squeezing, allowing higher production
rates.
Figure 3: A Manual Reamer
Fresh coconut meat is removed from the
shell using a manual reamer (Figure 3) or a
motorised reamer. The fine particles are
pressed in a similar way to extract the oil
emulsion. The emulsion is broken and the
oil is then separated and clarified (see
below).
Presses have a number of different designs, which can be grouped into screw or hydraulic
operation. Both types can be manual or motor driven. In all types, a batch of raw material is
placed in a heavy duty perforated metal ‘cage’ and pressed by the movement of a heavy metal
plunger. The amount of material in the cage varies from 5-30 kg with an average of 20 kg. Layer
plates can be used in larger cages to reduce the thickness of the layer of raw material and speed up removal of oil. The pressure should be increased
slowly to allow time for the oil to escape. Screw types are
more reliable than hydraulic types but are slower and produce
less pressure. Except where a lorry jack is used (Figure 4),
hydraulic types are more expensive, need more maintenance,
and risk contaminating oil with poisonous hydraulic fluid.
Ghanis are widely used in Asia but less so in other areas. A
heavy wooden or metal pestle is driven inside a large metal or
wooden mortar (Figure 5a). The batch of raw material is ground
and pressed and the oil drains out. They have relatively high
capital and maintenance costs and need skilled operators to
achieve high oil yields.
Figure 4: Hydraulic Oil Expeller
Mechanised extraction
Motorised presses are faster than manual or animal types
(Figure 5a) but are
more expensive.
Figure 5a: Animal Powered Extraction Figure 5b: Motorised Extraction
Motorised ghanis
(Figure 5b) are also
available, but their
higher capital and
operating costs require
a larger scale of
production for
profitability.
Expellers are
continuous in operation
and work by grinding
and pressing the raw
material as it is carried
through a barrel by a helical screw (Figure 6a). The pressure inside the barrel, and hence the
yield of oil, are adjusted using a ‘choke’ ring at the outlet. The equipment has higher production
rates than similar sized presses but is more expensive to buy and operate.
Figure 6a: Powered Oil Expeller Figure 6b: Manual Oil Expeller
Although manual expellers are available (Figure 6b), small scale oil millers more often use
powered equipment to reduce the time and labour involved in processing. Some designs also
have an electric heater fitted to the barrel to increase the rate of oil extraction. The production
rate using presses and ghanis depends on the size of the equipment and the time taken to fill,
press and empty each batch. The production rate of expellers depends on the size of the
equipment, the speed of the screw and the setting of the choke ring.
Clarification of oil
Crude (freshly extracted) oil contains moisture, and
fibre, resins, colours etc. from the plant material, which
make it darker and more opaque. These materials are
removed by clarification – either by letting the oil stand
undisturbed for a few days and then separating the
upper layer, or by using a clarifier (Figure 7). This
consists of an oil drum placed above a fire. The oil is
boiled to drive off water and destroy naturally occurring
enzymes and contaminating bacteria. The oil is
allowed to stand and contaminants the separate out.
The oil is filtered through a cloth and heated briefly to
100°C to boil off any remaining traces of moisture. This
is usually sufficient to meet the quality needs of
customers and give a shelf life of several months when
correctly packaged. However, the oil requires
additional refining stages of de-gumming, neutralising
and de-colouring to have a similar quality to
commercially refined oils, and these stages are difficult
to complete at a small scale.
Figure 7: A Clarifier
Packaging and storage of oil
If incorrectly stored, some types of oil rapidly go rancid and develop an unpleasant odour and
flavour. The main factors that cause rancidity (in addition to moisture, bacteria and enzymes
above) are light, heat, air and some types of metals. To obtain a shelf life of several months,
oils should be stored in lightproof, airtight and moisture-proof containers in a cool place. Tin
coated cans, glazed pottery, coloured glass and certain types of plastics are each suitable
when properly sealed. Great care is needed to remove all traces of oil from re-useable
containers, and to thoroughly dry them before re-filling, because any residual moisture or
rancid oil on the inside will rapidly spoil fresh oil. The materials used to make processing
equipment and containers should not contain copper as it promotes rancidity. Stainless steel,
galvanised iron, enamelled iron or aluminium are suitable.
Use of by-products
Coconut by-products (Figure 8) have a wide variety of uses. Groundnut meal is widely used for
human food (biscuits, soups etc.) when it is extracted by manual methods which do not burn
the by-product. Other fruits, nuts and oilseeds produce by-products that can be used for fuel
and animal feeds (Table 1). The high temperatures employed in expellers burn by-products and
they are only suitable for animal feeds. However, all oil extraction businesses need to identify
markets for their by-products for economic viability.
Quality assurance
The main quality checks concern raw materials, processing conditions, product quality and
packaging and storage conditions. Raw materials should be checked to ensure that there is no
mould growth, and that they are correctly dried, cleaned and sorted. During processing, the
temperature and time of conditioning, the moisture content of the raw material, and the yield of
oil should be routinely checked. Quality checks on the product include correct colour, flavour,
odour, clarity and fill weight.
Oil processing as a business
The profitability of oil processing depends on reducing the capital and operating costs as much
as possible, and at the same time maximising the income from the sale of oil and by-products.
A careful study of all costs should be undertaken before setting up a production unit. In
particular the cost of the main pieces of equipment, salaries for the expected number of
workers, and the prices for raw materials, fuel and power should be assessed.
The price that can be charged for oil and by-products depends on a number of factors including
quality, packaging, and the number, type and quality of competing products. These should
each be assessed in order to calculate the likely income at the planned scale of production
over the year. The production costs can then be compared with the expected income to
calculate the likely profitability. In most cases it is necessary to make full use of the byproducts
to make the enterprise financially successful.
Different systems are used for marketing and selling oils and by-products, and it is necessary
to select one that meets the needs of consumers, while at the same time keeping the costs of
selling as low as possible. For example, contract (or custom) oil extraction, in which farmers or
households bring their crop to the oil mill for processing, has the lowest selling costs.
Alternatively, oil can be sold from bulk drums into customers’ containers in markets or at the
production site, or it can be packaged into retail or bulk containers and transported to towns for
sale. By-products are usually sold in bulk to poultry or animal producers, or to other food or
animal feed processors. It may be advantageous to locate the oil mill in an area where byproducts
are needed in order to reduce transport costs.
One problem that faces oil processors is to ensure that there are adequate supplies of raw
material to operate at the planned production rate throughout the year. It is likely that crops will
be bought during harvest time when prices are lowest, but it may be necessary to offer an
incentive for farmers to supply the processing unit, rather than sell on the open market. A
simple contract to buy a specified amount of crop at a fixed price can benefit both farmers and
processors, provided both parties keep their side of the agreement. Oil processors also need a
large working capital to buy the year’s supply of seasonal crops, and adequate storage
facilities so that they remain in good condition until they are processed.
available, but their
higher capital and
operating costs require
a larger scale of
production for
profitability.
Expellers are
continuous in operation
and work by grinding
and pressing the raw
material as it is carried
through a barrel by a helical screw (Figure 6a). The pressure inside the barrel, and hence the
yield of oil, are adjusted using a ‘choke’ ring at the outlet. The equipment has higher production
rates than similar sized presses but is more expensive to buy and operate.
Figure 6a: Powered Oil Expeller Figure 6b: Manual Oil Expeller
Although manual expellers are available (Figure 6b), small scale oil millers more often use
powered equipment to reduce the time and labour involved in processing. Some designs also
have an electric heater fitted to the barrel to increase the rate of oil extraction. The production
rate using presses and ghanis depends on the size of the equipment and the time taken to fill,
press and empty each batch. The production rate of expellers depends on the size of the
equipment, the speed of the screw and the setting of the choke ring.
Clarification of oil
Crude (freshly extracted) oil contains moisture, and
fibre, resins, colours etc. from the plant material, which
make it darker and more opaque. These materials are
removed by clarification – either by letting the oil stand
undisturbed for a few days and then separating the
upper layer, or by using a clarifier (Figure 7). This
consists of an oil drum placed above a fire. The oil is
boiled to drive off water and destroy naturally occurring
enzymes and contaminating bacteria. The oil is
allowed to stand and contaminants the separate out.
The oil is filtered through a cloth and heated briefly to
100°C to boil off any remaining traces of moisture. This
is usually sufficient to meet the quality needs of
customers and give a shelf life of several months when
correctly packaged. However, the oil requires
additional refining stages of de-gumming, neutralising
and de-colouring to have a similar quality to
commercially refined oils, and these stages are difficult
to complete at a small scale.
Figure 7: A Clarifier
Packaging and storage of oil
If incorrectly stored, some types of oil rapidly go rancid and develop an unpleasant odour and
flavour. The main factors that cause rancidity (in addition to moisture, bacteria and enzymes
above) are light, heat, air and some types of metals. To obtain a shelf life of several months,
oils should be stored in lightproof, airtight and moisture-proof containers in a cool place. Tin
coated cans, glazed pottery, coloured glass and certain types of plastics are each suitable
when properly sealed. Great care is needed to remove all traces of oil from re-useable
containers, and to thoroughly dry them before re-filling, because any residual moisture or
rancid oil on the inside will rapidly spoil fresh oil. The materials used to make processing
equipment and containers should not contain copper as it promotes rancidity. Stainless steel,
galvanised iron, enamelled iron or aluminium are suitable.
Use of by-products
Coconut by-products (Figure 8) have a wide variety of uses. Groundnut meal is widely used for
human food (biscuits, soups etc.) when it is extracted by manual methods which do not burn
the by-product. Other fruits, nuts and oilseeds produce by-products that can be used for fuel
and animal feeds (Table 1). The high temperatures employed in expellers burn by-products and
they are only suitable for animal feeds. However, all oil extraction businesses need to identify
markets for their by-products for economic viability.
Quality assurance
The main quality checks concern raw materials, processing conditions, product quality and
packaging and storage conditions. Raw materials should be checked to ensure that there is no
mould growth, and that they are correctly dried, cleaned and sorted. During processing, the
temperature and time of conditioning, the moisture content of the raw material, and the yield of
oil should be routinely checked. Quality checks on the product include correct colour, flavour,
odour, clarity and fill weight.
Oil processing as a business
The profitability of oil processing depends on reducing the capital and operating costs as much
as possible, and at the same time maximising the income from the sale of oil and by-products.
A careful study of all costs should be undertaken before setting up a production unit. In
particular the cost of the main pieces of equipment, salaries for the expected number of
workers, and the prices for raw materials, fuel and power should be assessed.
The price that can be charged for oil and by-products depends on a number of factors including
quality, packaging, and the number, type and quality of competing products. These should
each be assessed in order to calculate the likely income at the planned scale of production
over the year. The production costs can then be compared with the expected income to
calculate the likely profitability. In most cases it is necessary to make full use of the byproducts
to make the enterprise financially successful.
Different systems are used for marketing and selling oils and by-products, and it is necessary
to select one that meets the needs of consumers, while at the same time keeping the costs of
selling as low as possible. For example, contract (or custom) oil extraction, in which farmers or
households bring their crop to the oil mill for processing, has the lowest selling costs.
Alternatively, oil can be sold from bulk drums into customers’ containers in markets or at the
production site, or it can be packaged into retail or bulk containers and transported to towns for
sale. By-products are usually sold in bulk to poultry or animal producers, or to other food or
animal feed processors. It may be advantageous to locate the oil mill in an area where byproducts
are needed in order to reduce transport costs.
One problem that faces oil processors is to ensure that there are adequate supplies of raw
material to operate at the planned production rate throughout the year. It is likely that crops will
be bought during harvest time when prices are lowest, but it may be necessary to offer an
incentive for farmers to supply the processing unit, rather than sell on the open market. A
simple contract to buy a specified amount of crop at a fixed price can benefit both farmers and
processors, provided both parties keep their side of the agreement. Oil processors also need a
large working capital to buy the year’s supply of seasonal crops, and adequate storage
facilities so that they remain in good condition until they are processed.
