Extracting and Refining Oil - Level 1&2 ISBN 978-99960-977-9-9 i
Extracting and Refining Oil Level 1 & 2 i
Extracting and Refining Oil - Level 1&2 iii
Table of contents Chapter 1: Extracting Crude Oil from pulse 1 Introduction 1 Identifying the types of pulses 1 Identifying equipment and machinery for Oil extraction 2 Oil extraction by pressing 8 Roasting pulses 8 Types of roasting 9 Importance of roasting 9 Milling the pulses 9 Pressing Pulses 10 Storing Oils 13 Chapter 2: Extracting Crude Oil from oil seeds 14 Identify oil seeds 14 Description of some of the common members of the oil seed group 14 Identify tools and machines 17 Clean the oil seeds 17 Activity 1 Pressing the pulses 20 Activity 2 Pressing oil seeds 21 Activity 3 Label the parts of the UNATA Press 22 Self-Assessment 23 Further Reading 23 Chapter 3: Refining Oil 24 Introduction 24 Identifying crude Oil 24 Identifying equipment and machinery 25 Objectives of refining 27 Manual method 29 Traditional Methods 30 Packaging 30 Labelling 31 Activity Refining Groundnut oil 32 Self Assessment 33 Further Reading 33 iv
Extracting and Refining Oil - Level 1&2 Acknowledgement The Ministry of Labour, Youth and Manpower Development, is so grateful to UNESCO for the financial and technical support in development of these books. Appreciation is also extended to Korean Research Institute for Vocational Education and Training (KRIVET), and Technical and Vocational Education and Training (TEVET) Authority for facilitation of the development of the curriculum. The following are also recognized for their special roles in different capacities in the development of the material; Malawi Bureau of Standards, Natural Resources College, Magomero Training College, Ministry of Agriculture, Irrigation and Water Development, Export Trading Group (ETG), Transglobe Produce Export Limited, DAPP Mikolongwe Vocational Training Centre, and all those who took part in the labour market assessment, development of the curriculum, validating, and development of this booklets. The Ministry also recognized the role played by journalists from different media houses in editing the booklet and LYPH Outlet for the designing of the material. v
Preface Malawi though being agro-based economy, has failed to maximise benefits from the agricultural trade because it has been taking raw produce to both domestic and international markets which is subject to declining terms of trade. The current Government agenda of transforming Malawi from predominantly importing to export led growth therefore needs a catalyst of skills development to enable the achievement of the goal. Skills have a fundamental place in turning the vision to reality and knowledge to products. This booklet is therefore part of the first curriculum that has been developed to achieve the stated national agenda as enshrined in the Malawi Growth and Development Strategy. The processing of the agroraw materials has the potential of contributing to the much desired economic growth through creation of jobs and employment, development of products, and increasing of income at large. The ultimate goal in all this will be the attainment of poverty reduction. Ministry of Labour, Youth and Manpower Development with support from UNESCO has developed this booklet on Extracting and Refining Oil Level 1 & 2 that aims at empowering both young and old, males and females in agro-processing skills which are applicable to the nation. The Government therefore is greatly indebted to UNESCO for the great technical and financial support through the Better Education for Africa's Rise Project in coming up with these booklets. It is the Ministry's belief that the trainers and trainees will use the booklet to their best in transferring and acquiring knowledge respectively. Godfrey B.C. Kafere, PhD ACTING SECRETARY FOR LABOUR, YOUTH AND MANPOWER DEVELOPMENT vi
Extracting and Refining Oil - Level 1&2 Introduction Most agricultural products must be processed before they can be used. Processing transforms raw agricultural commodities into a high value product. For example, groundnuts, soya beans, cotton; sunflower can be processed into oil. The by-product produced from the processing of oil from sunflower is seed cake which can be used as an animal feed. On completion of this module, the learner should be able to extract crude oil from pulses and oil seeds in the agro food processing industry and be able to refine the processed oil. During oil extraction process the operator should be conscious on quality, hygiene, safety and accuracy. vii
Chapter 1 Extracting Crude Oil from pulse Introduction Pulse is a type of leguminous crop that is harvested solely for the dry seed. Dried beans, lentils and peas are the most commonly known and consumed types of pulses. Pulses do not include crops which are harvested green (e.g. green peas, green beans) these are classified as vegetable crops. The following are the examples of pulses that can be used for oil extraction; black gram, green gram, pigeon peas. On completion of this learning outcome, the learner must have the following competencies: 1. Identify types of pulses 2. Identify equipment and machinery for oil extraction 3. Oil extraction by pressing 4. Roast pulses 5. Mill the pulses 6. Press the pulses Identifying the types of pulses Pulses among others include: all varieties of dried beans, kidney beans, lima beans, butter beans, broad beans, ground beans, chick peas, cowpeas, black-eyed peas, pigeon peas and lentils. The Figure below shows some of the pulses: Types of the pulses 1
Extracting and Refining Oil - Level 1&2 Identifying equipment and machinery for Oil extraction Extraction involves the separation of the raw materials into oil, oil residues, and cake. There are three types of extracting machines which include extruder, expeller and oil extractor. These extract oil through crushing, pressing and solvent extraction respectively. Oil extruders There are two types of extruders namely single and dual or duplex extruder. Below are the examples of extruder machines as shown in the figure below Single screw extruder This equipment consists of gearboxes offered by P.G.Drive. The following are the features of single screw extruder; improved power efficiency due to helical tooth gearing and reduced power tariff & operational cost that directly add to the profit for any business, it has inbuilt thrust HSG for better reliability, durability & space saving, and it has profile ground gears meeting international din quality standard to ensure low noise performance. 2
The Table below defines technical details for single screw extruder. Technical Details Spectrum Input Power (Pn) 2 to 250 kw Ratio (in) 5 to 18 Output Torque (T2) 346 to 25000 Nm Screw Diameter (D) 20 to 200 mm Dual or Duplex oil extruder Side view of dual oil extruder 3
Extracting and Refining Oil - Level 1&2 A dual extruder combines a first pass with low pressure and second pass at high pressure level. In this case the cake which is produced from the first conveyor is fed automatically to the second conveyor, which then leads to the middle section where the heating is being done at high temperature and oil is produced. Oil expeller/press Oil expellers can be categorized into two; manual and mechanical. Manual expellers are those which depend on human effort to press the oil out of oil seeds. Among these are Ram Press and UNATA Press specifically for groundnuts. These are cheaper. However, they have low efficiencies in production. On average their extraction levels are 90 percent. Manual Oil expeller 4
The mechanical oil expellers are those which are motorized or have hydraulic systems which enable and ease oil expelling. These have higher level pressing power and are of high oil extraction efficiency which on average 99 percent. However the mechanical oil expellers are of higher cost than the manual press. Below are the pictures of the two. Ram Press and Hydraulic Press 5
Extracting and Refining Oil - Level 1&2 The mechanical oil expellers are also of different types with the common being single oil expellers and dual expellers. In single screw oil expelling the drive can be operated by either an electric motor or diesel engine. Single screw oil expeller Single screw oil expellers have one screw shaft that moves the pressing dishes towards a pressing direction for extraction of oil. This expels oil in a single oil pass. The figure below depicts a screw expeller which is capable of producing the oil in a single pass. Single screw oil expeller Dual Expeller In the same respect as single screw expeller, there is also a dual oil expeller which combines a first pass at low pressure and second pass at high pressure. In this case, the cake which is produced from the first pass is fed automatically to the second stage. In principle duplex expeller 6
employs screw conveyor of varying pitch and differently shaped barrel areas. This arrangement increases the pressure as the material is forced through the barrel. Dual expeller Oil Extractor Oil extractors are machines that remove oil from the seeds with byproducts like cakes. These machines mill and heat the seed to produce oil. The figure below depicts a picture of an oil extractor. An oil extractor 7
Extracting and Refining Oil - Level 1&2 Oil extraction by pressing Operations and capacities vary from machine to machine. However, the general extraction mechanism is that the scorched seed is fed through the intake at lower pressure, the seed goes through a moving roller and driven towards a compressed point. In the process of moving higher temperature is generated, which facilitate the burning and change of enzymatic conditions of the seed. This combined with pressing, oil comes out into filtration chamber separating the oil from residues. Most of the oil is extracted in the middle section whereby the temperature is above 100 C. However, significant additional amount of oil is yielded by second pass. From this process, two products come out, oil and the cake as a by-product. It is worth noting afore that this is process oil which is not refined and edible. Roasting pulses Roasting, as shown in the figure below, is a cooking method that uses dry heat where hot air envelops or covers the food. The importance of roasting prior to oil extraction comes from the fact that oil is solid at room temperature. By roasting rises the temperature of the food product so that fat transforms into oil in the oil seed cells. Mini Roasting Machines 8
Types of roasting There are various methods of roasting. Some of them are broiling, grilling, deep frying and baking. Roasting can be done either manually (traditionally) or mechanically. Manual roasting is applied to light weight operations such as flying of groundnuts for home consumption as opposed to mechanical roasting which calls for higher capacities such as roasting of soybean in the process of oil extraction. Importance of roasting It helps in taking out detrimental enzymes and anti-growth factors that are hazardous to health. It softens the final product It improves digestibility and flavor of final product It reduces the cooking time Milling the pulses Milling is grinding or crushing of pulses into smaller particles. Other methods of oil extraction require size reduction by milling the pulses prior to oil extraction. The figure below shows side view of mill and oil extractor Mill and Oil extractor 9
Extracting and Refining Oil - Level 1&2 Pressing Pulses Oil extraction is the process of removing oil from seed/nut/plant such as algae. There are three main ways to extract oil such as cold oil pressing, expelling, and solvent extraction. The cold oil pressing and expelling involve the use of machines while solvent extraction involves the use of chemicals. Pressing pulses is done by a machine shown below, whereby the extraction of edible oils from pulses and oil seeds is done by using a press. Oil Pressing Machine At household level oil pressing is done using a simple machine which can be locally made. This machine is made from a car jack, either hydraulic or screwed, which pushes a shaft within a chamber towards a point where the pulse is compressed and allows oil to be released from the cells. Figures below shows Hydraulic, UNATA, and Ram press including their cross section (isometric view for hydraulic). It is worth noting that some of these can be manufactured locally even for home use. However, efficiency and optimization levels are lower. Hydraulic Press 10
1000 mm spindle 800 mm nut in bronze holes 330mm 10 mm pressplate 270 mm perforated cage bolts iron wood 70mm container UNATA Press 11
Extracting and Refining Oil - Level 1&2 Handle Piston pin Hopper Tie arms Pivot pins Piston Cage Compression cylinder Adjustable restriction cone Feed Gear box Feed Adjustable nut with spring Ram Press Feed screw Pressing screw Cone Perforated cylinder 12
Storing Oils Storing crude oil is of critical importance even though it is one of the final stages in the extraction. However, storage of the product has critical importance in the whole production. Among the conditions that must be taken into consideration when storing oil are temperature, light, and humidity. Temperatures affect the chemical composition of oil. Oil is fat at room temperature, the heating when extracting enables the change of fat to oil for ease extraction from the cells. When the temperatures are below room temperature then it returns to fat and can't be used in that form. It is however worth noting that fat storage helps increase shelf life and enables easy transportation. The disadvantage however is that it requires maintenance of the temperatures. This therefore needs high technology like air conditioned facilities. Oil contains nutrients which react with the ambient light. The reaction will result in changes of the extracted oil. Oil is carbohydrate, therefore the light will either hydrolyse or oxidize resulting in dis-colour of the oil, rancidity, and loss of flavour. In this reaction, light act as a catalysis of the ambient air and the oil. Humidity has close to similar effect on oil as is the light. Humidity increased the catalytic conditions of oxygen which increases the oxidation process. It also increases the water content in the ambient air, therefore decreasing the quality of oil. Considering the effects of the environment in which crude oil is stored, facilities and equipment for storing oil has to be selected carefully. Mostly oil is stored in drums (barrels), tanks, and containers which are either made of metal or plastic. The storage in these facilities or equipment depends on the state and temperature of the oil. Liquid oil is easily stored in drums with tight closures than fats. The storage therefore should consider the transitions of oil which largely depends on temperature. Furthermore, hot oil cannot be stored in plastic containers because it will rapture the container resulting to loss of oil. It has to be noted that boiling point of oil is higher than most substances including plastic, as such hot oil can be a source for rapturing. 13
Extracting and Refining Oil - Level 1&2 Chapter 2 Extracting Crude Oil from seeds On completion of this learning outcome, the learner must have the following competencies: 1. Identify oil seeds 2. Identify tools and machinery 3. Clean oil seeds 4. Crush oil seeds 5. Press oil seeds 6. Filter oil product Identify Oil seeds Oilseeds are staple foods for millions of poor people in developing countries, and are these days developing an even more important role as cash crops. The most important crops in these categories are oilpalm, beans (soybean, cowpeas, broad beans, red beans) and groundnuts. Further can be mentioned cashew, sheanut, sesame, sunflower, coconut and olives. Oilseeds add nutritional value to the diet by high quality protein and/or vegetable oil, together with oil soluble vitamins like vitamin A. Description of some of the common members of the Oil seed group Crops belonging to the oil seed group are divided into two subgroups: Major and minor. Among the major oil producing crops are; oil palm, coconut palm, groundnut and sheanut. Among the minor are sesame, melon, cotton, castor, sun flower, cocoa bean, kapok and locust beans. As far as Malawi is concerned, soya, groundnut and sunflower are considered as the most important group. The oil content varies in different species. Most contain 1% fat content but groundnuts and soya beans have a very high fat content, about 30% for soya beans and 49% in groundnuts. In Malawi several oil producing varieties exist. These are; a. Cotton Seeds Fitala b. Ground nuts c. Sunflower Chalimbana d. Soya CG 7 Makwacha Malimba Nansoko Manipinta e. Pigeon Peas RG1 MwaiWathuAlimi (White) Mawanga 1512 (white) 14
Cotton seed Cotton seed is obtained from the cotton bowl. The seeds are obtained after the fibres have been removed. When obtained from gin, cotton seed includes remnants of unginned lint and the fuzz. It yields an average 16 percent crude oil, 45.5 percent cake or meal, 25.5 percent hull and less than 1 percent linters. There is principal Chapter 1 poisonous pigment in the seed known as gossypol which interferes with protein digestion when consumed. Chickens and pigs are sensitive to the feed from cotton because of that Sunflower There are various varieties of sunflower: giant, semi dwarf and dwarf types. The seeds are contained in pocket like cells called achenes. The giant types are about 190-450cm tall with large heads, about 30 to 45 com in diameter. They are white or grey with black stripes and have rather lower oil content. The semi dwarf types are about 135-190cm tall and their heads are about 20-25cm in diameter. The seeds are smaller, black, grey or stripped and are higher in oil content than the giant types. The dwarf types are rather small but contain the highest amount of oil. The seeds can be eaten raw, roasted or salted. They are also used as livestock feed, and for poultry and cage birds. The seeds contain semi drying oil (20-35 percent of the seeds) which is pale yellow and of high quality. Groundnuts As a food crop groundnut Sunflower 15
Extracting and Refining Oil - Level 1&2 is one of the most important sources of edible oil and is mainly grown for this product. It contains 47-50% oil in shelled nut. Some varieties contain less oil content about 38-47 percent. It is rich in protein, containing about 30 percent, and it also contains some Groundnuts carbohydrate, about 10 percent. These constituents make groundnut one of the most concentrated food crops, high in energy. Groundnut protein is highly digestible and has many uses both for human and animal consumption. It is an excellent source of the B vitamins and high in Vitamin E. Soya beans Soya beans The nutritional content of soy depends on variety. Black seeded types are one of the richest in protein but low in oil. The yellow seeded one is high in oil but low in protein. The mature bean contains higher percentage of protein than any other beans except winged bean. The seed contains semi drying oil. The proportion depends (14-24 percent) depends on variety. Oil produced from soya is very useful in the manufacture of margarine and shortening, and is exclusively in the manufacture of paints, limonium, oil cloth, printing ink, soap, insecticides, disinfectants, detergents and also in pharmaceutical preparations. 16
The residue after the extraction of oil is very rich in protein. This is used in various food preparations. It is used in artificial adhesives, textile sizing material, water proofing material and firefighting foam. As a feed, soy bean cake is a good source of protein for cattle and poultry and the beans and haulm are good folder and as fertilizer. The seed are also used as green vegetables. Identify tools and machines There are different kinds of tools and equipment, and machinery used in extracting oils from oil seeds. Before oil extraction, the following tools and equipment are used for preparing the seed for oil extraction and maintenance of quality; Decorticators: These they help in removing the seed cort. Though sometimes these are also used in extracting oil. Dehullers: These machines help in removing the hard seed cort. Delinters: These remove lint from seeds. Copra cutters: This cuts the copra as means of size reduction. Seeds Cleaners: For maintenance of quality, the equipment helps in cleaning the seeds. Destoners: This helps in removing stones from the seed. Below are machinery used in oil extraction. These are the same as in extracting oil from pulses. Ram press UNATA press Hydraulic press. Clean the oil seeds This involves the removal of all foreign materials other than the oil seeds. It starts with sieving, sorting, grading and ends with polishing. 17
Extracting and Refining Oil - Level 1&2 Crush Oil seeds This refers to the breaking down of oil seeds into smaller particles in readiness for pressing. Usually machines are used to break down the oil seeds. This increases the surface area for heat penetration and absorption in readiness for pressing. Press oil seeds The extraction of oil from oil seeds using a press involves forcing the oil out of the plant cell at high extraction pressure. This can be achieved by employing compression, or vacuum extraction. Filter Oil The need for filtering oil is aimed at separating the oil from residues contained in the crude oil. During this process, biological membrane or heating is employed. For biological membrane filtration, the plant particles absorb or collect undesirable compounds from crude oil in the process of filtration. Membrane oil-filtration employs use of the following machines: plate and frame type chamber press vertical leaf tank or pressure filter centrifugal self-cleaning Local vertical filtration Furthermore, filtering by heat involves adding 1litre of crude oil to 10 parts of water and boil until all the water is evaporated. However, this method is energy intensive. It should be mentioned that there are two methods of refining edible oils namely Alkali refining (Classic chemical refining) and Physical refining. a) Alkali refining process can treat almost any kind of edible oils and fats but involves the production of soap stocks and has a refined oil yield lower than the one physically obtainable even if of more stable quality in the time. Below are the standard steps in the commercial refining process: Neutralization, Combined neutralization and Dewaxing, Bleaching Deodorizing 18
b) Physical refining basically consists of removing fatty acids by steam distillation under vacuum, which has the following advantages: Higher yield of refined product No soap stocks formation Lower quantity of polluted effluents Lower refining costs In comparison to the two refining systems the following facts in Table below should be considered. Table 2: Factors for consideration in oil refining systems Refining Method Chemical Method Physical Methods Applicability Almost no limit Not recommended for some oils and fats Final quality and storability Good to excellent limited storability Oil yield Standard Higher Bleaching agent requirements Standard Higher Degumming requirements - Very critical By products Diluted soap stocks Fatty acids and deodorizing distillates Effluents waters (Quantity/quality) Higher quantity/ Lower quantity/ heavy pollution minor pollution 19
Extracting and Refining Oil - Level 1&2 ACTIVITY 1 Pressing the pulses Task description After treating the pulses, you are requested to identify type of pulses, equipment and machinery, roast, mill, press and store oils. Time allocated for this activity is 4 hrs. Tools and materials required for the exercise. Extruder, expeller, hammer mill Trainer s Instructions Ensure trainees are given appropriate tools and materials Demonstrate how to extract oil Trainee s Instructions Select tools and materials for extracting oil Put on appropriate protective gear Identify type of pulses Identify equipment Roasting pulses Milling pulses Pressing pulses Storing oils Follow the procedures for extracting oil step by step Procedure for extracting oil Identify type of pulses Identify equipment and machinery Roast pulses Mill pulses Press pulses Store oils 20
ACTIVITY 2 Pressing oil seeds Task description After treating the oil seeds, you are requested to identify type of oil seeds, equipment and machinery, roast, mill, press and store oils. Time allocated for this activity is 4 hrs. Tools and materials required for the exercise. Extruder, expeller, hammer mill Trainer s Instructions Ensure trainees put on appropriate PPE Ensure trainees are given appropriate tools and equipment Demonstrate how to extract oil Trainee s Instructions Select tools and equipment for extracting oil Put on appropriate protective gear Identify type of oil seeds Identify equipment Roasting oil seeds Milling oil seeds Pressing oil seeds Storing oils Follow the procedure for extracting oil step by step Procedure for extracting oil Identify type of oil seeds Identify equipment and machinery Roast oil seeds Mill oil seeds Store oils 21
Extracting and Refining Oil - Level 1&2 ACTIVITY 3 Label the parts of the UNATA Press here below 1 12 2 13 14 15 3 4 5 6 7 8 9 10 11 22
Self-Assessment a) What is the difference between pulses and oil seeds? b) Mention two methods of extracting edible oil c) Differentiate the products of crushing and pressing? d) Give three types of crude oil storage facilities? e) Compare and contrast roasting and baking? Further reading Muhammad S. and Mark A.U., (2012) Dry beans and pulses: Production, Processing and Nutrition. Chavan and Pawar, (2012). Postharvest Management and Processing Technology: cereals, pulses, oilseeds, fruits and vegetables. Daya Publications, New Delhi. Pall W. (1998). Small-Scale Manufacture Of Compound Animal Feed, Natural Resources Institute. UK. 23
Extracting and Refining Oil - Level 1&2 Chapter 3 Refining Oil Introduction Crude oils as received from the extraction plant which contains several non-triglyceride components which must be removed. Refining processes comprises several processes that accomplish this aim of removing impurities through use of machines, modern technologies and traditional methods. In refining, physical and chemical processes are combined to remove undesirable natural as well as environmental related components from the crude oil. These components comprise of for example phosphatides, free fatty acids, pigments such as (chlorophyll), odours, flavours (including aliphatic aldehyde and ketone), waxes, as well as heavy metals pesticides. Learners are advised that while learning they should make an effort to improve their safety, time, cost and environmental consciousness. Learning Outcome On completion of this learning outcome, the learner must have the following competencies; Identify crude oil Identify tools and equipment Select method of oil refining Package refined oil Label refined oil Identifying crude Oil Crude oil can be obtained after extraction from various sources such as leguminous crops (groundnut, soya, sesame and oil seeds (baobab and sunflower). 24
Crude oil has a deep dark colour or extreme right as shown in the fugure below. Crude oil Identifying equipment and machinery Edible oils obtained from coconut, corn, cottonseed, olive, palm, peanut, soybean and sunflower etc. contain gums and other impurities which are removed by degumming, neutralizing and bleaching processes with the use of oil refining machines of various capacity 25
Extracting and Refining Oil - Level 1&2 Figure below shows an example of a complete edible oil refinery of 5- ton capacity 1&2-Neutraliser;3-Bleacher;4-Deodoriser;5-Cooler;6-Thermic Fluid boiler;7&8-filter Press;9-Raw oil tank;10-bleach oil tank;11&12-soap pan. The edible oil refinery can refine almost all types of oils. The refined oil quality depends on the type of crude oil and its chemical structure. Some refineries can have a higher capacity of up to 1000 litres or more depending on the design, requirements and specification. Factors affecting selection of machine for oil refining include capacity of the refinery and the nature of crude oil. For example on capacity, a refinery of capacity ranging from 1-5 tonnes can be used to refine palm oil, palm kernel oil, peanut oil, rapeseed oil, cottonseed oil, sunflower oil, corn germ oil, animal oil among others. Nature of crude oil involves viscosity which is determined by the source of crude oil. The viscosity affects choice of sieves to be used when crude oil is being refined. 26
Objectives of refining Most crude oils contain impurities that must be removed before further processing can take place. These impurities can include; Solid particles (such as dirt), gums, free fatty acids, pigments and substances that affect smell and taste. Removal of undesirable products from crude oils is crucial in ensuring the desired product quality, and the way it is done must comply with required standards. Preservation of valuable vitamins such as vitamin E ortocopherolnatural anti-oxidants Minimising oil losses Minimising oil losses Protection of the oil against degradation. Select Method of Oil Refining Methods of refining crude oil to include; mechanical, manual and traditional Mechanised method use oil refineries which are done as follows: degumming, neutralizing, bleaching, and deodorizing. Step 1 - Degumming This is the first stage in the refining process. It is used to separate the gums, phospholipids, proteins and impurities that are insoluble in oil when hydrated. Importance of degumming is because it removes the emulsification of phospholipids which increases oil losses during alkali refining and may lead to brown discolourisation of oil after heating during deodorization There are two main types of gums that need to be removed such as hydratable phosphatides (NHP) that are easy to remove and Non-hydra table phosphates(nhp) which are hard to remove from oil such that they require the use of acid to convert to hydratable for complete removal. Degumming technique comprise of the following processes: Water degumming: treatment of crude oil with hot water to remove hydratable phospholids. Water degumming is commonly used with palm and coconut oils and is not associated with significant oil loss, saponification or environmental pollution. 27
Extracting and Refining Oil - Level 1&2 Dry acid degumming: treatment of crude oil with phosphoric acid, citric acid, oxalic acid or maleic anhydride. In this treatment, the acid is dispersed in oil followed by raising the ph with a base and some trapped triglycerides. Wet acid degumming uses very small amount of water to increase degree of hydration. Enzymatic degumming is modification of phospholipids with enzymes to obtain the water soluble compounds. Step 2 - Neutralizing The purpose of neutralization is to remove free fatty acids (FFA) that are responsible for the oil acidity. There are two different processes in this operation, the Alkali Neutralization and the Distillative Neutralisation. The usual method of alkali neutralization is treatment with weak lye. The method comprises the conversion of FFA in soaps and dilution of the resulting soaps in water phase. These soaps are removed by separators. In the separation stage other undesirable substances such as gums, oxidized component, metal ions, pigments and insoluble impurities are also removed. In distillative neutralization (physical refining) the free fatty acids are continuously removed from the crude oil with water vapor normally after degumming. Step 3 - Bleaching The major purpose of bleaching is the removal of undesired colour materials in the oil. Heated oil (~85 O C) may be treated with various bleaching agents such as fuller s earth, activated carbon, or activated clays. Many impurities, including chlorophyll and carotenoid pigments, are adsorbed onto such agents and removed by filtration. However, bleaching also promotes lipid oxidation since some natural antioxidants are removed together with the impurities. Bleaching is done with acidactivated clay minerals to absorb colouring components and to decompose hydro peroxides. Step 4 - Deodorising This is usually the last stage of the refining process of edible oils. Deodorizing is done to remove volatile components, mainly aldehydes and ketones, 28
with low threshold values for detection by taste or smell. Deodorization is essentially a steam distillation process carried out at low pressures (2-6 mbar) and elevated temperatures (180-220 C). For some oils, such as sunflower oil or rice bran oil, a clear table product is obtained by a dew axing step or crystallization of the wax esters at low temperature, followed by filtration or centrifugation. Two main refining routes are alkaline refining and physical refining (steam stripping, distillative neutralization) which are used for removing the free fatty acids. Figure 3 below is a flow diagram of the major processes in the refining process according to method. The classical alkaline refining method usually comprises the following steps; Manual method Manual method involves the removal of fatty acids by a steam distillation (stripping) process similar to deodorization. The low volatility of fatty acids (depending upon chain length) requires 29
Extracting and Refining Oil - Level 1&2 higher temperatures in physical refining than those required for only deodorization. In practice, a maximum temperature of 240-250 C is sufficient to reduce the free fatty acid content to levels of about 0.05-0.1 percent. A prerequisite for physical refining is that phosphatides be removed to a level below 5 mg phosphorus/kg oil. In the classic refining process, this level is easily achieved during the neutralization stage, but special degumming processes may be required for physical refining of high-phosphatide seed oils. These procedures rely on improved hydration of phospholipids by intimate contact of the oil with an aqueous solution of citric acid, phosphoric acid andlor sodium hydroxide, followed by bleaching (Segers and van de Sande, 1988). Traditional Methods Traditional methods include roasting, crushing to break cells in order to release the fatty acids, squeezing and sieving. Some of the traditional methods are as follows; Clean, dry and roast the raw materials, cooling, crushing in mortar or grinding in mills of the seeds, squeezing the rushed material in a manual oil press till oil starts dripping from it and collecting the oil. At this stage the oil can be further filtered or it is collected in withholding tanks where is it left for a number of days through a process of sedimentation. The sediments remain in the tank bottom and the refined oil form a clear top layer. It is then checked and packed in bottles and containers for safety. Packaging Various packaging materials are used for refined oil to ensure that the oil quality is maintained and protected from damage and spoilage. Plastic containers are a relatively new means of edible oil packaging due to their comparatively low price and low weight. The polymers most frequently used are PET, HDPE, and PVC. Although they do not provide as long a shelf life as metal containers, they are economical compared to tinplate and therefore suitable for use where a very long shelf life is not required. 30
Figure below shows oil in packages of 1-5 litres. Metal containers for vegetable oils are manufactured using tinplate or aluminium and in two different ways such as bottom and top closed at the metal fabrication plant with an orifice on the top for subsequent sealing and capping or bottom seamed onto the body blank and the top closed only after filling and bottling. Figure below shows the plastic, metallic (aluminium) containers for packaging oil. Aluminium is also employed as a packaging material for edible oils as it is light and very resistant to corrosion. Glass containers are widely used for bottling olive oils and virgin olive oils in particular. This is due not only to marketing requirements but also because glass containers prevent the permeation molecules into the bottle, slowing down the autoxidation rate. Labelling Labelling is required by law and must appear on food products including refined oil. It helps to provide information such as manufactured date, ingredients, best before, storage, usage general information about the product. Further information can be added to labels such as the amounts of polyunsaturated, monounsaturated, starch, cholesterol, vitamins or minerals. 31
Extracting and Refining Oil - Level 1&2 ACTIVITY Refining Groundnut Oil Task description After obtaining the groundnuts crude oil, you will be required to put crude oil into a machine, filter crude oil, refine, package and label for storage. Time allocated for this activity is 2 weeks. Below is a list of tools and equipment for this exercise. Tools and materials required for the exercise. Holding tank, drums, bottles, labeling material, boxes, filtering machine, expeller, oil press Trainer s Instructions Ensure trainees put on appropriate PPE Ensure trainees are given appropriate tools and materials Demonstrate how to carry out each activity. Trainee s Instructions Select tools and materials for handling raw materials Put on appropriate protective gear Prepare storage facility Identify crude oil Identify tools and equipment Select method of oil refining Package Label Follow the procedures for refining oil step by step Procedure for refining oil Identify crude oil Place in oil refinery Check after refining Pack in containers and bottles Label containers Store refined oil 32
Self Assessment a) Identify agro sources of crude edible oil? b) Mention three types of refining methods c) Classify packaging materials for refined oil? d) What are the factors to consider when labelling products? e) How can you maintain quality of refined oil? f) What is the most important information required when labelling? Further Reading Dunford N.T and Durnford H.B (2004) Nutritionally enhanced Edible Oil Processing FAO Publication (2010) Fats and Oils in Human Nutrition Wilson et al (2013) Edible Oils Processing. John wiley and Sons Inc. Woffham, et al. (2013) Edible Oils Processing. John wile and Sons.Inc Segers,J.C. and R.K.K.M.(1988) Proceedings of the world conference on edible fats and oils. Muhammad Siddiq and Mark A.Uebersax (2012) Dry beans and pulses: Production, processing and nutrition Oi Mig Lai et al (2012) Palm Oil Production and Processing Characterisation and uses.aocs Press. 0 Chavan U and Pawar, V. (2012). Postharvest Management and Processing Technology: cereals, pulses, oilseeds, fruits and vegetables. Daya Publications, New Delhi. George A, (2010) Principles of Crop Production, Theory, Techniques and Technology. Eastern Economy Edition 33
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Extracting and Refining Oil - Level 1&2