Oils and Fats

Oil And Fats:-

Vegetable oil and fats are lipid material drived from plants.Physically oils are liquid at room temperature and fats are solid. Chemically fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerene in their structure. Although many plant yield oil but in commercial practice oil is primarily extracted from seeds.

The melting temperature distinction between oils and fats is imprecise, since definitions of room temperature vary, and typically natural oils have a melting range instead of a single melting point since natural oils are not chemically homogeneous. Although thought of as esters of glycerin and a varying blend of fatty acids, fats and oils also typically contain free fatty acids, monoglycerides and diglycerides, and unsaponifiable lipids.

Vegetable fats and oils may or may not be edible. Examples of inedible vegetable fats and oils include processed linseed oil, tung oil, and castor oil used in lubricants, paints, cosmetics, pharmaceuticals, and other industrial purposes.

Oil Extraction and/or Expression Methods:-

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 businessRaw material preparatioOilseeds and nuts should be properly dried before storage, and cleaned to 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 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.

Dehusking:-

Dehusking is important to give high yields of oil and reduce 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. Some seeds (e.g. groundnuts) are conditioned by heating to 80-90oC using a seed scorcher (    2) and all oil-bearing materials need to have the correct moisture content to maximize 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 mechanized 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 method:-

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 ghazis. Pulped or ground material is loaded into a manual or hydraulic press to squeeze out the oil water emulsion. This is more efficient at removing oil than traditional hand squeezing, allowing higher production rates. Fresh coconut meat is removed from the shell using a manual reamer (    3) or a motorized 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 Meta 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 a Manual Reamer 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, 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. 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.

Mechanized extraction

Motorized presses are faster than manual or animal types (    5a) but are more expensive.Motorized ghanis 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. 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.Although manual expellers are available 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 ghazis 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 fiber, resins, colors etc. from the plant material, which make it darker and more opaque. These materials are removed by clarification – either by letting the oil stands undisturbed for a few days and then separating the upper layer, or by using a clarifier. 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, neutralizing and de-coloring to have a similar quality to commercially refined oils, and these stages are difficult to complete at a small scale.

Packaging and storage of oil:-

If incorrectly stored, some types of oil rapidly go rancid and develop an unpleasant odour andflavour. 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, colored 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, galvanized iron, enameled iron or aluminum is suitable.

Use of by-products:-

Coconut by-products 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 viabThe 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 maximizing 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.