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close this bookTraining Programme for Women Entrepreneurs in the Food-processing Industry - Volume II (UNIDO, 1985, 286 p.)
close this folderChapter 2 Vegetable Oil Extraction
View the document(introduction...)
View the document2.1 Oilseeds
View the document2.2 Groundnut/Palm Kernel
View the document2.3 Coconut
View the document2.4 Palm Fruit

2.4 Palm Fruit




Remove fruit from bunches, manually operated machine available.


Pulp manually with pestle and mortar or more quickly with motorised pulper.


Press 15-20 kg in 20-60 mins. (Fig. 4) Emulsion extracted.


Heat to 80-90° C to break emulsion.

Skim oil

Small clarifier available (Fig. 6) Clarify.


Pack in lightproof, airtight containers.


Store away from heat, sunlight etc., shelf life 2-12 months expected depending on packaging and storage conditions.



Some raw materials (for example groundnuts, sunflower seed) require decorticating and winnowing. The husk is removed because if left on it 1) has no value as animal feed, 2) it absorbs oil and 3) it increases the weight of material to be transported and processed. However in groundnut processing some fibrous material is needed. It allows the oil to escape from the press or expeller, and also prevents the nuts turning into peanut butter without releasing the oil. Some husk (about 10%) is therefore added back to the nuts to increase the yield of oil. However too much husk reduces the value of the oil cake as human food. Skill is therefore needed to judge the balance between the amount of husk needed for proper processing and the amount which reduces the value of the oilcake.

Oil extraction from dry crops

In all raw materials the oil is contained in oil bearing cells which must be ruptured to release the oil. The best way of rupturing the cells depends on the structure of the food. In some (for example groundnuts, dried coconut, palm fruit) pressure applied in a press is sufficient, whereas in others (for example avocado, oilseeds) a rubbing or "shearing" action is also needed. Traditional methods rely on pounding and sqeezing manually but this is time consuming and hard work. The output is not usually enough for income generation and the oil quality is very variable. Improved equipment for extraction of oil falls into two categories: presses, which only apply pressure and screw expellers which apply both pressure and a shearing action. A third method, used in large scale extraction, uses a solvent to dissolve the oil, but is not suitable for small scale operation due to 1) the high capital costs of equipment, 2) the need for solvents which may not be easily available and 3) the risk of fire or explosions.


There are a large number of different types of presses but the principle of operation is similar for each. A batch of raw material is placed in a heavy metal "cage" and a metal plunger is used to press the material. The main differences in design are as follows: 1) the method used to move the plunger 2) the amount of pressure in the press, 3) the size of the cage. The plunger can be moved manually or by a motor. The motorised method is faster but more expensive. Different designs use either a screw thread or a hydraulic system (for example a lorry jack) to move the plunger. Higher pressures can be obtained using the hydraulic system, but care is needed to make sure poisonous hydraulic fluid does not contact the oil or raw material. Hydraulic fluid can absorb moisture from the air and lose its effectiveness, and jacks also wear out and need frequent replacement Screw threads are made from hard steel and held by softer steel nuts so that the nuts wear more quickly than the screw. These are easier and cheaper to replace than the screw. The size of the cage varies from approximately 5 kg - 30 kg with an average size of 15 kg. The pressure should be increased gradually to allow time for the oil to escape. If the depth of the raw material is too great, oil will be trapped in the centre. To prevent this, heavy "layer Plates" can be inserted in the raw material. The production rate of presses depends on the size of the cage and the time needed to fill, press and empty each batch. Hydraulic presses are faster than screw types and powered presses are faster the manual types. Some types of manual press require a considerable effort to operate.


A rotating screw pulls the raw material from a hopper into the barrel where the seed is broken and pressure is gradually increased as it moves through the barrel. Oil passes through narrow slots in the barrel and press cake is discharged from the end through a 'choke' ring. This ring is adjustable to control the pressure in the barrel. The screw rotates at about 100 rpm and heat is generated due to friction between the seeds and the screw/barrel. Some designs have additional electric heaters around the barrel. The screw, choke ring and barrel all wear and must be repaired and replaced at intervals. There must therefore be mechanical skills available locally to carry out the maintainence and repair work. Sand or grit in the raw material reduces the time between repairs from several months to as little as two weeks and proper cleaning of the raw material is therefore essential.

Oil extraction from wet crops

Palm fruit is reruced to a fine pulp and the oil emulsion is pressed out. The remaining fibre is washed and the water added to the emulsion. The liquid is then heated to break the emulsion and the separated oil is skimmed off.


Crude oil from both wet and dry crops contains a suspension of fine pulp and fibre from the plant material with small quantities of water, resins, colours and bacteria which make it darker and opaque. These contaminants are removed by clarifying the oil, either by allowing it to stand undisturbed for a few days and removing the upper layer, or by using a clarifier. If the oil is still not sufficiently clear for the consumer's requirements, it can be filtered through a plastic funnel fitted with a fine filter cloth. Finally the oil is heated to boil off traces of water and destroy bacteria. When these impurities are removed the shelf life of oils can be extended from a few days to several months, provided proper storage conditions are used.

Refining of oil

Oil from large scale production is further refined by degumming (removing dissolved proteins and other plant materials), neutralising fatty acids and bleaching any colours in the oil. This is rarely necessary for small scale producers who are supplying domestic customers, but one or more of these stages may be necessary for export markets. The correct control of these stages (particularly neutralisation) requires more complex chemical determinations and analytical equipment than is likely to be available for small scale producers.



The heat treatment during processing and low water content of oil reduces the risk of bacterial food poisoning almost completely. The most important risk is from a mould that can grow on nuts or seeds that are not fully dried, which produces a poison called 'aflatoxin'. This is a highly dangerous poison and all precautions should be taken to dry raw materials properly and keep them dry before use. This is a particular problem with groundnuts and these should be shelled before storage to prevent mould growth beneath the shell.

Raw material control

Crops should be harvested when fully mature, as they then contain most oil and it is easily removed. Under-ripe materials give a lower yield of oil and are more difficult to process. Over-ripe fruits are easily bruised and this allows enzyme action and bacterial growth which reduces the oil yield and causes rancidity. Maturity is judged with experience, by the colour/size of the raw materials. Raw materials must be in prime condition because any deterioration leads to a rancid, unpleasant flavour in the oil. Oilseeds, copra etc. that are dried and stored before processing should be stored in weatherproof, ventilated rooms (Fig. 9) and should be protected against insects, rodents and birds. They should be fully dried before storage as inadequate drying and/or poor storage conditions allow mould growth. This causes spoilage which reduces the oil yield and may affect the oil flavour and colour in addition to the risks from aflatoxin.

Seeds and nuts in particular should be cleaned using a screen or sieve to remove soil, sand and grit which would rapidly wear out equipment Leaves, stalks, seeds from other plants and stones should be picked out

Process control

The main quality control point is conditioning of the raw materials by heating with small amounts of water. The degree of conditioning is critical. If the temperature is too high the material dries out, if it is too moist the oil yield is reduced. In practice the raw material should not be sticky (too wet) but also should not fall apart easily (too dry). The correct moisture content can be found by experience or by analytical determination. In addition gentle pressure should be applied to allow the oil to escape. Measurement of the oil yield is routinely made (% oil from raw material - see Table 1).

Product control

The main quality factors for oil are colour, clarity, taste/flavour and odour. Correct colour and clarity are mainly due to proper clarification after the oil has been extracted. The taste and odour of oil result from the type of raw material used and the extent of rancidity. The crude oil produced on a small scale is not usually refined to remove flavour and colour.

Table 1: Raw materials for edible oil production


content (%)

content (%)

(% from oilseed)

Uses for


Seeds and beans





cooking soap

animal feed






animal feed (needs detoxifying)











animal feed






(hulls used for chicken litter, presscake for animal feed)

Safflower seed





animal feed


Coconut fresh








skin cream











food (snacks, soup) animal feed

Palm kernal nuts




cooking, skin cream

animal feed

Shea nut




soap cooking

fuel (shells) fuel


Oil Palm










skin cream






cooking, skin cream

animal feed fuel

* Traditional methods


Rancidity during storage is reduced by using clean, dry containers, excluding light and heat and avoiding contact with metals.

The main factors that cause rancidity during storage are

1) oxidadve rancidity, which takes place in air and is accelerated by light, the presence of copper and iron from machinery/containers and by high temperatures. Oil should be stored away from heat or sunlight, in a lightproof and airtight container which is filled to the top, and does not have iron or copper on the inner surface.

2) hydrolytic rancidity is caused by enzymes present in the raw materials or produced by contaminating bacteria. Bacteria grow on the oil if moisture, plant material or dust are present. The enzymes increase the levels of fatty acids and cause rancidity. This can be prevented by filtering the oil after extraction, heating oil to remove moisture and destroy enzymes and bacteria, and preventing moisture pickup during storage by using moisture proof containers.


In view of the factors that cause rancidity described above, and the need to contain the oil without leakage, suitable storage containers include sealed glass or plastic bottles, preferably made from coloured glass or kept in a dark box, metal oil cans, where the metal is tin coated (to prevent oil from reaching the iron of the can), or glazed ceramic pots, sealed with a cork and wax stopper. Great care should be taken to properly clean oil containers if they are to be reused. A film of old, rancid oil on the inside of an empty container will quickly make fresh oil go rancid. The containers should be properly dried after cleaning to remove all traces of moisture. If correct storage conditions are not used the shelf life of the oil is reduced from many months to as little as a few days or weeks. Oilcake should be dried to prevent mould growth and stored in a cool dark place to prevent rancidity of oil remaining in the cake. It should be protected from insect and rodent attack using the same methods as those used for the raw material.


Oilseeds have a long storage life if sufficiently dry and oil processing can therefore continue throughout the year, thus making better use of equipment (compared to more seasonal products). The low volume of oil makes transport and distribution easier and distribution to a wider area also creates a larger potential market Producers can therefore receive an income throughout the year.

Byproducts contain protein and residual oil and are valuable as animal or human food (Table 1). Byproducts also have a long shelf life if properly dried and this allows income generation throughout the year. The potential income from oil extraction is often high enough to justify the relatively high costs of setting up and operating a production unit.

Potential disadvantages to oil extraction include the higher value of oilseeds compared to other crops and hence the higher financial risk from losses, the need for fuel, and the time-consuming and hard work. Equipment is relatively expensive and year-round production needs a large working capital to buy and store seasonal crops. There is also the risk of competition from large scale producers who are able to market high quality oils at a lower cost because of economies of scale.

Small scale extraction processes usually produce crude oil which has a different appearance and flavour to commercially refined oil. It is therefore essential that market surveys for consumer acceptability are conducted before production starts. Other considerations to running a smale scale oil extraction project include

1) The local demand for vegetable oils,

2) Sufficient raw material in the area for year-round work and adequate transport and storage facilities,

3) The relative prices of raw materials, crude oil, and oilcake to ensure profitability,

4) Availability and cost of materials and equipment,

5) Organisational/marketing skills available.


· Sieve/screen 1-2mm mesh
· Decorticator (Fig 7)
· Winnower
· Heat conditioning pan or seed scorcher (Fig 3)
· Press (Figs 4, 4a) or Expeller (Fig 5, 5a & 5c)
· Clarifier (Fig 6)
· Bottle filler and sealer or film sealer
· Nut cracker
· Coconut scraper (Fig 8)
· Palm fruit bunch stripper
· Pulper
· Storage facilities (Fig 9)

Further Reading

Oil processing

GATE Oil presses: an introduction (GATE/GTZ Publications, Eschborn, Germany, 1979)

UNIDO Appropriate industrial technology for oils and fats (United Nations, New York, 1979)

UNIDO Guidelines for the establishment and operation of vegetable oil factories (United Nations, New York, 1977)

CORBETT, S A new oil press design: but is it any better? VITA News, (Vita Pubs, Washington DC, 1981)

RAO, P.V.S. A study of village oil industry in India (Appropriate Technology Development Association, Lucknow, 1980)

BOYD, JOHN A buyer's guide to low-cost agricultural implements (Intermediate Technology Publications Ltd., London, 1976)

GODIN, V.G., and SPENSLEY, PC. Oil and Oilseeds, Crop and Product Digests No. 1 (TPI, London, 1971)

German Adult Education. Make your own oil. Association Africa Bureau, Ghana, (traditional palm oil processing)

NWANZE, S.C., The hydraulic hand press. Nigerian Institute for oilpalm research, 4 (15), (1985)

HARTLEY, C.W.S., and NWANZE, S.C. Factors responsible for the production of poor quality oil. The Oil Palm, pp 68-72. (Tropical Products Institute, London 167 pp., 1965)

ACHAYA, K.T. Appropriate technology for production and processing oils and fats. Paper presented at International Forum of Appropriate Industrial Technology (UNIDO, New Delhi, 1978).

SRIKANTA RAO, P.V, A search for appropriate technology for the village oil industry (ATDA Pubs. Lucknow, India, 1978)

TPI Oil and oilseeds. Crop and Product Digests, No 1, London, (1971) Palm oil TPI Processing of oil palm fruit and its products (TPI Pubs, London, 1973) BLAAK, G.A village palm oil mill. Oil palm news, 23,5-11, (1979)

CORNELIUS, J.A. Processing of oil palm fruit and its products (London: Tropical Products Institute, 95pp, 1983)

KING-AKERELE, 0. Traditional palm oil processing, women's role and the application of appropriate technology (United Nations Economic Commission for Africa 1983 ST/ECA/ATRCW/82/02, 1983)

COWARD, L.D.G. Assistance in the design of a prototype palm oil extraction press for rural areas SI/CMR/82/801 Cameroon (UNIDO. Vienna, 1985)

ATA, J.K.B.A. Processing and quality characteristics of Ghanaian commercial palm oils Ghana Journal of Agricultural Science, 7(2), 147-149, (1974) BERGER, K. Production of palm oil from fruit. Journal of the American Oil Chemists' Society, 60, 158A - 162A, (1983)

CORNELIUS, J.A. International standards for palm oil. Journal of the American Oil Chemists' Society, 54943A-948A, (1977)

COURSEY, D.G. The deterioration of palm oil during storage. Journal of the West African Science Association 7(2), 101-115, (1963)

HARTLEY, C.W.S. The oil palm (2nd Ed. Longmans, London, 806 pp, 1977)

JOHNSON, R.M. and Elaeis RAYMOND, W.D. The African oil palm, guineensis. Colonial Plant and Animal Products, 4(1), 14-23, (1954)

JACOBI, C. Palm oil processing with simple presses GATE Magazine (GATE/GTZ, Eschborn, Germany, 1983)

MACLELLAN, M. Palm oil Journal of the American Oil Chemists' Society, 60, 320A - 325A, (1983)

DONKOR, P.A hand-operated screw press for extracting palm oil. Appropriate Technology vol 5, No 4. (1979)

NWANZE, S.C. Semi-commercial scale palm oil processing. The Oil Palm, pp 63- 66. (Tropical Products Institute, London 167 pp., 1965)

RUTOWSKII, A. Traditional palm oil processing in Western Africa. Fette Seifen Anstrichmittel, 85 (7), 262-267., (1983)

TCC Extraction of palm oil using appropriate technology hand screw press. (Technology Consultancy Centre Report, Ghana, 1978)

BOWEN, B.H.A screw press for low cost palm oil extraction. Engineering Research Publications Research Paper No TE12, (Univ of Sierra Leone, Freetown, Sierra Leone, 1976)


ATEN, A., MANNI, M., and COOKE, F.D. Copra processing in rural industries. FAO Agricultural Development Paper, No. 63 (FAO, Rome, 1958)

GRIMWOOD, B.E. Coconut palm products (FAO, Rome, 1976)

HAGENMAIER, Robert D Coconut aqueous processing (San Carlos Publications, Cebu City, Philippines, 1980)

THEIME, J.G. Coconut oil processing (FAO, Rome, 1968)

TPI Development of a wet coconut process designed to extract protein and oil from fresh coconut. (TPI, London, 1973)

ILO Small scale oil extraction from groundnuts and copra. (ILO Pubs, Geneva, 1983)

BANGOR, J., and and VELASCO, J.R. Coconut production utilisation. Philippine Coconut Research and Development Foundation Centre, (PCRDF), Amber Avenue, Pasig, Metro Manila, Philippines.


HAMMONDS, T.W. HARRIS, R.V., MACCFARLANE, N. The small-scale expelling, of sunflower seed oil in Zambia. Appropriate Technology Journal, vol 12, No 1. (IT Pubs, London)

NIESS, T. New shea-butter technology for West African women. GATE Magazine GATE/GTZ Pubs, Eschborn, Germany, 1983)

BULK, J.V.D. UNATA Press No. 4, Heuvelstraat, 131,3140 Ramsel, Belgium, (1986)

TPI Rural Technology Guide 10 A hand-operated disc mill for decorticating sunflower seed. (TPI Pubs, London 1981)

TPI Rural Technology Guide 9 A hand-operated disc mill for decorticating sunflower seed. (TPI Pubs, London, 1981)

TPI An economic study of lauric oilseed processing (TPI Pubs, London, 1973)









Figure 9 STORAGE