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Guide to make edible oils |
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SEPTEMBER 2005 Author: G. Blaak
The author worked for 30 years in developing countries in a great variety of agricultural projects worldwide. He worked as Senior Officer Industrial Crops with the Food and Agriculture Organization (FAO) of the United Nations in Rome and was involved in projects involving the cultivation and processing of industrial crops such as tea, rubber, coconut, sugarcane, coffee, cocoa, essential oil crops, oilseed crops, fibre crops. During his career the author received numerous requests from farmers, development agencies and local authorities how to improve farmers income. Of course the introduction of improved varieties, better agronomic practices and crop protection help only temporarily the individual farmer until his colleagues catch up with him. A more permanent income improvement can be made by transformation of the crop on the farm. In general a big profit (value added) can be realized that is otherwise realized by the large scale processors. Successful examples of on-farm transformation are fermentation of fresh cocoa pods to cocoa beans, sugarcane to brown sugar, fresh tea leaves to green tea, essential oils by steam distillation of freshly harvested aromatic plants, making chocolate from cocoa beans, latex from rubber trees to ribbed smoked sheets and oilseeds to oil and press cake to a protein rich animal feed. Many development organizations realized that on farm transformation of oilseeds to oil and press cake could considerably improve farmer’s income. The oil can be sold in the local market and the press cake could serve as a protein concentrate in animal feed for local farmers. The great value added in processing oilseeds on-farm lays in the fact that it by-passes the oilseed buyer, the seed processor and the oil wholesaler supplying the market women. Now the oilseed producer can become also the oil retailer in the local market. This guide provides information about on-farm production of edible oils with a low cost oil expeller that also has a high oil extraction efficiency. THE INTRODUCTION OF SUCH A LOW COST, MANUALLY OPERATED OIL EXPELLER COULD BE SEEN AS A MICRO-PROJECT OF A HOME INDUSTRY FOR WOMEN IN LOW INCOME COUNTRIES. The minimum annual requirement of oils and fats is between 8.5 – 10.0 kg per adult according to the World Health Organization. Edible oils and fats are essential for good health. However, in many countries there is a great scarcity of edible oils and as a result the price of one kilogram oil is frequently more than the daily wage of a labourer! Many national and international organizations as well as private companies have developed manually operated oil presses for small scale entrepreneurs or small groups of farmers. The aspect of manual operation is important as the poorer segment of the rural population in many countries is frequently too poor to consider mechanization of processing by using an electromotor or petrol engine. Such an investment in mechanization far exceeds their borrowing capacity. In this guide only a manually operated oil expeller, the PITEBA OIL EXPELLER, will be considered in view of the low exploitation and maintenance cost. A number of small scale oilseed presses are in use. An example is the ancient Ghani, an ox-driven device in the Far East. The oil yield per hour and the extraction efficiency are low. More recent developments are the various piston driven devices that compress oilseeds in a cylinder (press cage) under high pressure. The oil escapes through openings in the press cage. The piston is forced with a very long lever into the press cage. This is very tiresome work. The Bielenberg-, New Dawn and the Yenga press are examples of piston presses in use. The Yenga press is used in Zambia to produce sunflower oil. Information from FAO learns that about 50 kg sunflower seed can be processed per day yielding 13 kg oil. The total oil content in undecorticated sunflower seed is about 45% or 22.5 kg oil in 50 kg sunflower seed. The extraction efficiency is: 13/ 22.5 x 100% = 58%. Thus about 42% of the oil remains in the press cake. The press cake has good economic value as a protein concentrate in animal feed. However, the residual oil content in the press cake is too high to be used as the sole or major protein concentrate in animal feed. The Yenga press is operated by 2 persons. The price quoted for the press is US$ 163. The maintenance costs are US$ 2,78 (ZMK 2,500) per day. The press is relatively a too high investment cost for the target group of users. The investment cost is US$ 81.5/employee. The daily oil production 6.5 kg/employee. The New Dawn press, made in South Africa, is a sturdy piece of equipment with a processing capacity of 100 kg sunflower seed per day. The press is operated manually by 3 persons. The extraction is 22.5 – 29.7 kg (25 – 33 litres) oil per day. At 45% total oil to seed this is an extraction efficiency of 50 – 66%. A similar extraction as with the Yenga press. It means that also with the New Dawn press 34 – 50% of the oil is left in the press cake. The New Dawn press costs US$ 450 excluding crating and freight cost. At a weight of 100 kg the freight cost may be considerable, when exporting. The cost price of this press may be well beyond the borrowing capacity of the low income, small scale oil crop cultivating farmer. About 3 Yenga presses could be bought against one crated New Dawn press. Three Yenga presses have a combined daily capacity of 150 kg seed against 100 kg for the New Dawn press. The investment costs are at least US$ 160/employee. The daily oil production is 7.5 - 9.8 kg/ employee. It is clear that there is a market for a cheaper manually operated oil press with a much better oil extraction efficiency. 4. SOME THEORETICAL ASPECTS OF OILSEED PRESSING To understand the oil pressing operation one has to understand what happens with the oilseed during pressing. The oil in the oilseeds is locked up in tiny plant cells . Only when these plant cells are broken, the oil is released and can be extracted by, for example, applying pressure. The very hard kernels (seeds) of the oil palm contain about 68% oil. Pressing whole kernel yields little oil. Grinding the kernel to small pieces yields more oil. However, passing the kernels through a hammer mill, as used for producing maize flour, results in a good oil extraction. The reason is that in the hammer mill the oil containing plant cells are properly broken and the oil is released. The problem with the piston operated oil presses is the insufficient breakage of the oil cells. Inside the press cage the pressure on a plant cell is more or less equal from all directions and the cell will not break. Another problem is the temperature of the seed in the press cage during pressing. The oil will have a lower viscosity (will be more watery) at a high temperature and will escape easier from the seed, when it is compressed in the press cage. These problems can be resolved by using a different type of oil press as described in the following chapters. The following objectives were formulated for a newly designed oil press:
Manually operated screw expellers were in use in The Netherlands during World War II to expel oil from rapeseed. After a long search such an expeller was found in a farm implement museum. Replicates of this expeller were made and during the subsequent years drastic changes in the design were made:
However, a number of properties of the ancient model should be maintained such as: the manual operation by one person, the sturdiness in construction, the absence of the need for spare parts and the low cost of the expeller. Most important feature of the ancient screw expeller was its good ability to break the oil containing cells during the oil expelling process due to a high friction within the press cake, when under pressure. 6 THE DEVELOPMENT OF THE PITEBA OIL EXPELLER
The press cage should be heated for about 15 minutes with a small lamp oil burner, mounted under the end of the press cage, before starting oil expelling. The burner uses 4 – 5 millilitre (4 – 5 grams) oil per hour. One litre lamp oil can serve for about one month of processing. Heating the press cage during oil expelling greatly improves the extraction efficiency. The heating liquefies the oil escaping from the press cake at the end of the expeller. The hotter the oil, the easier it is squeezed from the press cake. Also hot oil flows better to the oil outlet. Some seeds develop so much friction (heat) within the press that the flame can be reduced during expelling as is the case with hammer milled oil palm kernel. The temperature at the end of the press cage will normally be around 50 – 70 degrees centigrade. This means that the oil can still be considered as a result from cold pressing and will maintain its natural flavours. 7. PREPARATION OF OILSEEDS BEFORE EXPELLING THE OIL 7.1 Removal of dirt Sand is regularly present in seed as seeds are frequently dried on the ground or on mats in many countries. Sand will wear out the screw of the expeller. A simple, cheap plastic strainer (sieve) with holes that are smaller than the seeds concerned can serve to remove sand. Bigger pieces like small stones, small sticks and pieces of flower heads can be removed with a plastic strainer that will allow passage of the seed but not the dirt. Such bigger pieces of dirt may wedge between the screw and the press cage wall. The crank will be difficult to turn and the screw may be damaged. Thus a few simple strainers with holes of different size are part of the equipment of the oil maker. These low cost strainers are normally available in the local market. Some seeds are too big and are not grasped easily by the expeller screw. They have to be reduced in size to improve the throughput of the seed. This is the case, for example, with dried coprah, oil palm kernel, babassu kernel, unshelled groundnuts and beechnuts. Crushing the seeds in a big wooden mortar, as found in most villages, is most effective. The pounding will crush the oil cells in the seed and the oil will be liberated. This results in a better oil extraction than grinding to small pieces, because the oil cells are not necessarily broken in the grinding (cutting) process. Grating of fresh coprah and drying of the grated coprah afterwards seems to be effective in case of the coconut. 7.3 Drying of oil seeds Oilseeds should be properly dried before expelling the oil. Normally dry rapeseed contains 8% moisture. Increasing the water content to 11 – 12 % sharply reduces the extraction efficiency. In general seed has the correct water content when normal farm procedures in drying and storage are followed. 8. INVENTORY OF A PITEBA OIL EXPELLER A good number of simple gadgets are needed to operate the oil expeller beside the expeller and the bench.
9. THE POTENTIAL USERS OF THE PITEBA OIL EXPELLER During winter not much is growing on the fields in Northern Pakistan, Nepal, Tibet, Northern India, Bhutan, P.R. China. Mustard seed, rape seed, linseed , sunflower seed, hazelnuts, walnuts could be processed during the winter months. Similarly not much is growing on the fields in those countries with a pronounced hot dry season. Seed from sesame (sim sim), undecorticated sunflower seed, nigerseed, safflower, pumpkin, unshelled groundnut and hemp can be expelled with the PITEBA expeller. Kernels from the oil palm and babassu palm can be processed as well as the coprah from the coconut. Even beechnuts from the beech tree provide a good oil, that develops a nice scent during frying. ALL THESE OILSEEDS CAN BE PROCESSED WITH THE MANUALLY OPERATED PITEBA OIL EXPELLER. THE EXPELLER COULD BE INTRODUCED AS MICRO PROJECTS IN RURAL AREAS SERVING FARMER’S WIVES AND LANDLESS LABOUR TO EARN A SUBSTANTIAL ADDITIONAL INCOME. 10. A WORKING DAY IN THE LIFE OF AN OIL PRODUCER Assume the oil maker is a Zambian woman making sunflower oil at home from undecorticated seed. Assume that she works 8 hours, of which 6 hours in actual oil expelling and 2 hours for odd jobs such as cleaning seed, decanting oil from the previous day, cleaning bottles and bottling of oil. She starts the day by unlocking the cupboard (toolbox) underneath the bench and removes the 2 strainers for removal of respectively sand and coarse dirt. She sifts about 24 kilogram of seed, the quantity for the day. Afterwards she takes the vertical board and bolts the board with 4 butterfly nuts to the bench and she attaches the expeller with 2 butterfly nuts to the board. She fills up the oil reservoir of the burner with lamp oil and ignites the burner. In the mean time she uses a few drops of edible oil to grease the washer near the crank. She installs the plastic funnel on top of the seed inlet of the expeller. She installs the receptacles for the oil and the press cake on the bench. She cleans the oil outlet slit of the expeller with a kitchen knife to ensure a free flow of the oil. Three buckets are placed beside the bench: one for seed, one for oil and one for press cake. She makes sure she has a small wooden stick at hand to correct any bridge formation of seed in the funnel. She removes the terminal adjustment bolt as the bolt is not needed for sunflower seed expelling. She sits down on the bench and fills the inlet funnel with sunflower seed. By this time the expeller has been heated sufficiently to start processing by turning the crank at about 55 - 60 rounds per minute. If the turning goes lightly turning can be done faster and this increases the oil output per hour. This depends somewhat on the size of the seeds and the thickness of the seed shell of the sunflower variety. Every 30 minutes she can take a 10 minutes break and do some other odd job. At the end of the day she will have processed 22 kg seed and collected about 6 hours x 1.2 kg oil/hour = 7.2 kg oil (8 litres) and 22 kg – 7.2 kg = 14. 8 kg press cake. The oil extraction on seed will be 35%. The oil extraction efficiency will be around 75 – 78% assuming the use of seed with a total oil content of 45% on undecorticated seed. With small seeded, undecorticated sunflower seed with a total oil content of 45% up to 1.5 kg oil/hour i.e. 9 kg oil ( 10 litres) per 6 hours has been obtained. The extraction efficiency was 85%. However, at such a high extraction efficiency turning of the crank may not be sustained unless it is a well trained oil maker. At the end of the day she cleans the expeller by unscrewing the press cage cap (swivel) and turning the crank a few times. She replaces the press cage cap. She puts a few drops of oil on the washer near the crank of the expeller. All utensils and pieces are put into the cupboard underneath the bench. She locks the cupboard (toolbox). The oil is kept in a warm place overnight in the house. Any dirt will settle during the night. A warm place keeps the oil warmer and thinner so that dirt can settle faster. The press cake should be stored airtight in a drum or in big plastic bags. This will avoid attraction of water during storage especially during the rainy season. Moulds develop easily on press cake left in the open and make it unsuitable as an animal feed. Data from FAO were received indicating various costs such as:
The PITEBA expeller delivers 1.2 kg oil/hour. In the following economic analysis it will be assumed that the lady will sell her oil and press cake at a 10% discount at home. Thus ZMK 3.870/kg sunflower oil and ZMK 300/kg press cake. Lampoil is estimated at ZMK 4,000/litre. Depreciation of the expeller at ZMK 180/kg oil (US$ 0.20/kg oil). Income
Expenditure
Profit per working day
The total investment of
US$ 100, at ZMK 900/US$, could be repaid within
The expeller can be repaid at least within one month and credit for such a short period may not be a problem. A more up to date analysis can be made by inserting the most recent prices within this analysis. 10.3 Secondary income from oil expelling Assume that during 4 months/year oil is produced during 4 days a week or during 17 weeks x 4 days/week = 68 days. (This means processing 1.5 ton sunflower seed or a crop of 1.5 hectares rain fed sunflowers.) It means that 14.2 kg press cake/day x 68 days = 965 kg press cake is accumulated. Assume a laying hen needs 125 grams of feed/day. Thus a chicken needs 0.125 kg/day x 365 days = 46 kg feed/year. With the availability of 965 kg of press cake the oil maker could keep 965 kg feed : 46 kg/chicken = 20 chicken and one cock. Raising chicken may also earn an extra income within the compound. The economic analysis of the chicken business is not within the context of this guide. It might be more profitable to keep the press cake than to sell it. Also the chicken excrements are a very valuable plant nutrient that may serve raising some vegetables or fruit trees near the compound. 10.4 Income, expenditure and profit per day for processing rape seed in Pakistan in 2002
At Rs 40/US$ and US$ 100 total investment the press can be repaid from the profits in US$ 100 : (Rs 284 : Rs 40/US$) = 14 working days or within processing 300 kg rape seed. A more up to date analysis can be made by inserting the most recent prices within this analysis. Based on figures supplied by FAO in Nairobi the following economic analysis can be made for processing undecorticated sunflower seed in Kenya.
At an investment cost of US$ 100 and an exchange rate of KSh 79/ US$ (2002) the investment can be recovered in US$ 100 : ( KSh 459 : KSh 79/US$) = 17 working days. An up to date economic analysis can be made by inserting the most recent prices in this analysis. 10.6 Income, expenditure and profit per day for processing Niger seed in Ethiopia in 2004 Basic data were provided by Birale Agricultural Development PLC in Ethiopia.
10.7 Income, expenditure and profit per day for processing rape seed in Ethiopia in 2004 Basic data were provided by Birale Agricultural Development PLC in Ethiopia.
In this analysis no value is assumed for the 18 kg press cake that is produced per day. However, FAO publications indicate that protein feed for milk cattle may contain up to 50% rape seed cake. Pig rations may contain 5% rape seed cake without causing problems. If the cake can be sold this will add about Birr 9 to the daily profit at Birr 0.5/kg press cake. A total investment of US$ 100 could be repaid from the profits in US$ 100 : ( Birr 22 : Birr 8/US$) = 36 working days. However, if the press cake can be sold for Birr 0.5/kg, the repayment time will be much shorter i.e. US$ 100 : (Birr 31 : Birr 8/US$) = 26 working days. A more up to date economic analysis can be made by inserting the most recent prices. 11. PERFORMANCE OF THE PITEBA OIL EXPELLER FOR VARIOUS OIL SEEDS In this section general information will be provided on oilseeds that can be processed, quantities of oil/hour , percent oil extraction and extraction efficiency. Precise instructions about specific processing requirements for each seed type will be provided with the supply of the expeller.
Table 1. P
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The PITEBA
screw expeller is presented in the photograph. Inside the press cage is
the expeller screw. At the end of the press cage is a cap (swivel)
screwed on the press cage. A terminal adjustment bolt can be screwed
into the cap. In the cap are two holes. With the adjustment bolt the
openings in the cap can be adjusted. This adjustment is specific for
each type of seed processed. Some seeds such as seeds from sunflower,
Niger seed, pumpkin, safflower, hemp can be expelled without using the
terminal adjustment bolt . Cleaning of the press can be done by
unscrewing the swivel. Afterwards the crank is turned a few times and
the press cage is cleaned out. Some seed may be put into the funnel and
pass through the expeller without using the swivel. This will clean out
the press cage. A cheap seed inlet funnel can be made from the top of
most plastic soft drink bottles. A slit under the seed inlet funnel
serves as the oil outlet. A washer at the top of the expeller screw is
used to avoid direct contact between screw and press cage. It is the
only part that needs replacement due to wear.