2.5.1. Introduction
2.5.2. The site
2.5.3. Design and construction of the building
2.5.4. Equipment
2.5.5. Packaging materials
All fruit and vegetable processing operations require an hygienically designed and easily cleaned building to prevent products from becoming contaminated during processing. The two main sources of contamination are 1) insects and animals and 2) micro-organisms. Insects and animals are attracted to food buildings if foods or wastes are left lying round after production has finished. Micro-organisms can grow in food residues that are left on equipment, tables or floors which have not been properly cleaned. Micro-organisms require water to grow (Section I, Introduction) and wet processing therefore has an inherently greater risk of contamination than dry processing does. However, some types of micro-organism can form inert spores that are able to survive under dry conditions and then grow when they come into contact with water or foods and strict hygiene should also be enforced in drying operations. In dry processing there is an additional risk of contamination by dust, which can spoil foods itself and also harbour micro-organisms. The following aspects of setting up a processing facility should therefore be addressed by entrepreneurs, whether they are constructing a new facility or converting an existing building.
The location of a food building is very important and the following aspects need to be considered when choosing a site:
· location in relation to raw material supplies and likely markets· ease of access for staff (public transport, distance down an access road)
· quality of road access (all year, dry season only, potholes that may cause damage to products, especially when glass containers are used)
· nearby swamp land that would be a source of smells and insects
· any potential contamination of water supplies upstream of the processing site
· available land for waste disposal away from the building
· electricity supplies
· cleared land to reduce problems caused by insects and birds (preferably planted with short grass, which acts as a dust trap for airborne dust).
Roofs and ceilings
Walls
Windows and doors
Floors
Lighting and power
Water supply and sanitation
Layout of equipment and facilities
In general, a building should have enough space for all production processes to take place without congestion and for storage of raw materials, packaging materials and finished products. However, the investment should be appropriate to the size and expected profitability of the enterprise to reduce start-up capital, the size of any loans taken out and depreciation and maintenance charges.
In tropical climates, overhanging roofs keep direct sunlight off the walls and out of the building. This is particularly important when processing involves heating, to make working conditions more comfortable. Fibre-cement tiles offer greater insulation against heat from the sun than galvanised iron sheets do. High level vents in roofs both allow heat and steam to escape and encourage a flow of fresh air through the processing room. The vents must be screened with mesh to prevent insects, rodents and birds from entering the room. If heat is a serious problem, the entrepreneur could consider fitting electric fans or extractors, although this clearly increases capital and operating costs.
Rafters or roof beams within the processing and storage rooms are unacceptable. They allow dust to accumulate, which can fall off in lumps to cause gross contamination of products. Similarly, insects can fall from them into products. They also allow paths for rodents and birds, with consequent risks of contamination from hairs, feathers or excreta. It is therefore essential to have a paneled ceiling fitted to any processing or store-oom, with careful attention when fitting them to ensure that there are no holes in the paneling. Care should also be taken to prevent birds, rodents and flying insects gaining access to the processing room through gaps in the roof structure or where the roof joins the walls.
As a minimum requirement, all internal walls should be rendered or plastered with a good quality plaster to prevent dust forming in the processing room. An experienced plasterer should be used to ensure that no cracks or ledges remain in the surface finish, which could accumulate dirt and insects. The lower area of walls, to at least 1.08 metres (four feet) above the floor, is most likely to get dirty from washing equipment, from product splashing etc. and special attention should be paid to ensure that this area is easily cleaned. Higher areas of walls should be painted with a good quality emulsion. The lower parts of walls should be either painted with a waterproof gloss paint, preferably white, to allow them to be thoroughly cleaned, or ideally they should be tiled with glazed tiles. If tiling a process room is too expensive, it is possible to select particular areas such as behind sinks or machinery and only tile these parts. In some countries there is a legal requirement for specified internal finishes and this should be checked with the Ministry of Health or other appropriate authority (see also Section 2.4.2)
Window sills should be made to slope for two reasons: to prevent dust from accumulating and to prevent operators from leaving cloths or other items lying there, which in turn can attract insects. Windows allow staff to work in natural daylight, which is preferable to and cheaper than electric lighting. However, in tropical climates there is a natural inclination for workers to open windows to allow greater circulation of fresh air. This provides easy access for flying insects, which can readily contaminate the product. Windows should therefore be fitted with mosquito mesh to allow them to be left open.
Normally doors should be kept closed, but if they are used regularly there is again a tendency for them to be left open with similar consequences of animals and insects entering the plant. In this case, thin metal chains or strips of material that are hung vertically from the door lintel may deter insects and some animals, while allowing easy access for staff. Alternatively mesh door screens can be used. Doors should be fitted accurately so that there are no gaps beneath them and all storeroom doors should be kept closed to prevent insects and rodents from destroying stock or ingredients.
Figure 37 - A well-designed processing room
It is essential to ensure that the floors of processing rooms and storerooms are constructed of good quality concrete, smooth finished and without cracks. In some developing countries, it is possible to buy proprietary floor paints or vinyl based coatings, but these are usually very expensive. Generally, it is not adequate to use the red wax floor polishes that are commonly found in households, as these wear away easily and could contaminate either products or packages. Over time, spillages of acidic fruit products react with concrete and cause it to erode. Attention should therefore be paid to cleaning up spillages as they occur and to regularly monitor the condition of the floor.
The comers where the floor and the walls join are places for dirt to collect. During construction of the floor, it should therefore be curved up to meet the wall. It is possible to place fillets of concrete (or 'coving') in the comers of an existing floor to fill up the right angle, but care is needed to ensure that new gaps are not created which would harbour dirt and insects.
The floor should slope at an angle of approximately 1 in 8 to a central drainage channel. At the end of a day's production, the floor can be thoroughly washed and drained. Proper drainage prevents pools of stagnant water forming, which would in turn risk contamination of equipment and foods. The drainage channel should be fitted with an easily removed steel grating so that the drain can be cleaned. Where the drain exits the building, there is a potential entry point for rodents and crawling insects unless wire mesh is fitted over the drain opening. This too should be easily removed for cleaning.
General room lighting should be minimised wherever possible. Full use should be made of natural daylight, which is both free and better quality light, especially for intricate work. Where additional lighting is needed, florescent tubes are cheaper to operate than incandescent bulbs. However, if machinery is used that has fast moving exposed parts, these should be lit with incandescent bulbs and not tubes. This is because even though the parts should have guards fitted, a rotating machine can appear to stand still if its speed matches the number of cycles of the mains electricity that powers fluorescent tubes - with obvious dangers to operators.
All electric power points should be placed at a sufficiently high level above the floor that there is no risk of water entering them during washing the floor or equipment. Ideally, waterproof sockets should be used. It is important to use each power point for one application and not use multiple sockets which risk overloading a circuit and causing a fire. If there are insufficient power points for the needs of a process, additional points should be installed, even though this is more expensive. All plugs should be fitted with fuses that are appropriate for the power rating of the equipment and ideally the mains supply should have an earth leakage trip switch. If three-phase power is needed for larger machines or for heavy loads from electric heating, it is important that the wiring is installed by a qualified electrician to balance the supply across the three phases.
Water is essential in nearly all fruit and vegetable processing, both as a component of products and for cleaning. An adequate supply of potable water should therefore be available from taps around the processing area. In many countries, the mains supply is unreliable or periodically contaminated and it is therefore necessary for the entrepreneur to make arrangements to secure a regular supply of good quality water each day. This can be done by installing two high level, covered storage tanks either in the roof-space or on pillars outside the building. They can be filled alternately when mains water is available and while one tank is being used, any sediment in water in the other tank is settling out. As sedimentation takes several hours, the capacity of each tank should be sufficient for one day's production. The tanks should have a sloping base and be fitted with drain valves above the slope and at the lowest point. In use, water is taken from the upper valve and when the tank is almost empty, the lower valve is opened to flush out any sediment that has accumulated.
Water that is included in a product should be carefully treated to remove all traces of sediment and if necessary, it should be sterilised. This is particularly important if the product is not heated after water has been mixed in as an ingredient.
There are four ways of treating water at a small scale: by filtration; by heating; by ultra-violet light and by chemical sterilants, such as hypochlorite (also named 'chlorine solution' or 'bleach'). Other water treatment methods are generally too expensive at a small scale of operation.
Filtration through domestic water filters is slow, but having made the capital expenditure, it is relatively cheap. Larger industrial filters are available in some countries. Heating water to boiling and holding it at that temperature for 10-15 minutes is simple and has low capital costs, but it is expensive because of fuel costs and it is time consuming to do routinely. Heating sterilises the water but does not remove sediment and boiled water may therefore require filtering or standing to remove sediment.
Ultra-violet light destroys micro-organisms in water and commercial water treatment units that use this principle (Figure 38) are coming down in price to the point that they can be suitable for those small scale processors that use a lot of water. Again, this method does not remove sediment from the water.
Finally, chemical sterilisation using hypochlorite is fast, relatively cheap and effective against a wide range of micro-organisms. Cleaning water should contain about 200 ppm of chorine and water that is used as an ingredient should contain about 0.5 ppm to avoid giving a chlorine flavour to the product. A chlorine concentration of 200 ppm can be made by adding 1 litre of bleach to 250 litres of water and a 0.5 ppm solution is obtained by adding 2.5 ml of bleach to 250 litres of water. Although chlorine kills most micro-organisms, it also has a number of disadvantages: it can corrode aluminium equipment; it can taint foods; bleach must be handled with great care as it damages the necessary, the concentration of chlorine in water can be measured using a chemical dye that produces a colour when it reacts with chlorine. The intensity of the colour is compared to standard colours on glass discs in a 'comparator'.
Good sanitation is essential to reduce the risk of product contamination and to deter insects, rodent and birds. All wastes should be placed in bins and not piled on the floor. Processes should have a management system in place to remove wastes from the building as they are produced, rather than letting them accumulate during the day. Wastes should never be left in a processing room overnight. This aspect is described further in Section 2.7.2, and summarised in Appendix I.
Figure 38. - Ultra-violet water steriliser
(Courtesy of UV Systems Ltd.)
Good sanitation is essential to reduce the risk of product contamination and to deter insects, rodent and birds. All wastes should be placed in bins and not piled on the floor. Processes should have a management system in place to remove wastes from the building as they are produced, rather than letting them accumulate during the day. Wastes should never be left in a processing room overnight. This aspect is described further in Section 2.7.2, and summarised in Appendix.
The different areas required for fruit and vegetable processing are shown in Figure 39 for a drying unit and in Figure 40 for other types of production. The layouts of these processing rooms show how raw materials move through a process and through the room without paths crossing. Different stages in a process should be physically separated wherever possible. This helps prevent contamination of finished products by incoming, often dirty, raw materials and clearly identifies areas of the room where special attention to hygiene is necessary. This is particularly important to prevent contamination arising from activities such as bottle washing in which inevitable breakages produce glass splinters that could contaminate a product. This separation also reduces the likelihood of accidents or of operators bumping into each other.
Perishable raw materials should be stored separately from non-perishable ingredients and packaging materials. A separate office allows records to be filed and kept clean and provides a quieter working environment for book-keeping. Toilets should either be housed in a separate building or two doors should exist between them and a processing area. All workers should have access to hand-washing facilities with soap and clean towels. Laboratory facilities are generally not needed in fruit and vegetable processing, although a separate table for conducting quality assurance checks or check-weighing packages of finished product (Section 2.7.2) could be located in the office or in a separate area of the processing room.
Dried products
Boiled, concentrated and pasteurised products
Fermented and distilled products
Packaging, filling and sealing equipment
When selecting equipment, it should be the correct size for the intended scale of production (obtained from the Feasibility Study, Section 2.3.3). Managers should devise regular maintenance and cleaning schedules and ensure that they are followed. Further details on these topics are given in Section 2.7.1, Production Management and Section 2.7.2, Quality Assurance.
All types of fruit and vegetable processing require basic equipment to handle, weigh and prepare raw materials, such as buckets, tables, knives, and scales. Ideally, two sets of scales are used, one with an accuracy of +/- 0.1g to accurately weight small amounts and a second having an accuracy of +/- 50g for larger amounts of raw materials. However, scales are expensive to buy in most countries although the cost of small, electronic domestic scales is falling (Figure 41). A cheaper alternative to buying scales is to calibrate scoops or other measures, so that they contain the correct quantity of material when filled level with the top. In operation, scoops are faster than weighing, but the level of accuracy may be lower and careful training of operators is needed to ensure that the weights are consistent.
Because of the acidic nature of fruits, the parts of equipment that are in contact with foods should be made from either food grade plastic, aluminium or stainless steel. Other metals, such as mild steel, brass and copper should not be used because they react with the fruit and cause off-flavours or colour changes in the product. In general, because of its high cost, stainless steel is only used for cutting blades, boiling pans etc..
Wooden tables are cheaper in most countries than metal ones, but they are more difficult to keep clean. Ideally, wood should be covered in a sheet of thick plastic, aluminium or a 'melamine' type surface for easier cleaning. Details of methods for hygienic handling and storage of equipment are given in publications in the Bibliography and are summarised in Appendix I.
Figure 39. - Layout of a building for drying of fruit and vegetables
Figure 40. - Layout of a building for wet processing of fruit and vegetables
Figure 41. - Small electronic weighing scales
The process flow chart for dried foods (Figure 10) indicates a number of processing options depending on the type of product that is made. For example vegetables are frequently blanched by placing them in a wire basket and dipping them into a pan of boiling water (Figure 42). Alternatively they can be placed on wire mesh in a steam chamber. Fruits are often sulphured or sulphited to protect their colour. Sulphite dips are contained in a tank made from food grade plastic and sulphuring cabinets, comprising a wooden box, fitted with mesh trays, can easily be made from locally available materials.
Figure 42. - Blanching vegetables before drying
At larger scales of operation, there are a range of machines that can be used for preparation of fruits and vegetables. These include cleaners, de-stoners, peelers, cutters and slicing or dicing equipment (for example Figure 9). Details of equipment and suppliers are given in publications in the Bibliography. In the following Section, the types of equipment that are used to make dried fruits and vegetables, boiled and pasteurised products and wines, vinegars and spirits are described.
Fruits for crystallising are soaked in syrup using food grade plastic tanks and aluminium pans for boiling the syrup. A series of tanks are used to gradually increase the concentration of syrup over 3-4 days (Figure 11), which also allows greater utilisation of sugar compared to single stage soaking. In most countries, sugar contains dust and other contaminants and syrups should therefore be filtered through muslin cloth before use.
A number of different types of drier can be used, depending on the level of investment that can be justified from the feasibility study. A comparative summary of cabinet dryers in relation to other types of dryer is shown in Table 23. Solar dryers have some advantages over sun drying when correctly designed. They give faster drying rates by heating the air to 10-30°C above ambient, which causes the air to move faster through the dryer, reduces its humidity and deters insects.
Table 23. - A comparison of different drying technologies
|
Type of Dryer |
Cost ($) |
Capacity (kg wet food per day) |
Investment ($ per kg of dry food) |
Fuel efficiency |
Labour requirement |
|
Brace solar |
50 |
10 |
50 |
n/a |
very low |
|
Solar cabinet |
70 |
30 |
23 |
n/a |
very low |
|
McDowell |
170 |
40 |
43 |
very poor |
low |
|
Wood burning |
340 |
80 |
43 |
very poor |
low |
|
ITDG fuel fired batch |
3,400 |
240 |
140 |
poor |
high |
|
ITDG fuel fired semi-continuous |
6,800 |
360 |
190 |
medium |
very high |
|
Small commercial cabinet |
85,000 |
500 |
1,700 |
good |
high |
|
Large commercial cabinet |
170,000 |
2,500 |
680 |
good |
medium |
|
Tunnel (12 carriage) |
145,000 |
6,000 |
240 |
good |
low |
|
Moving band |
800,000 |
48,000 |
170 |
very good |
very low |
n/a - not applicable(From Try Drying IT, by Axtell and Bush, courtesy of IT Publications)
The faster drying reduces the risk of spoilage, improves the quality of the product and gives a higher throughput, so reducing the drying area that is needed. However, care is needed when drying fruits to prevent too rapid drying which would result in case hardening (see glossary) and subsequent mould growth. Solar dryers also protect foods from dust, insects, birds and animals. They can be constructed from locally available materials at a relatively low capital cost and there are no fuel costs. They may therefore be useful
1) where fuel or electricity are expensive, erratic or unavailable,
2) where land for sun drying is in short supply or expensive,
3) where sunshine is plentiful but the air humidity is high, and
4) as a means of heating air for artificial dryers to reduce fuel costs.
This last application is likely to gain in importance as fuel prices increase or to reduce dependence on imported fuels. Solar drying is not likely to be useful where the quality of sun dried foods is acceptable to local consumers and where the additional costs of solar drying are not recovered from increased value of the food.
In situations where the control over drying conditions is insufficient using solar dryers, it is necessary to use a fuel-fired dryer. Again, there are a large number of different types and the selection depends on the required throughput, types of fuel and level of investment that are available. The main limitations of fuel-fired dryers, in addition to higher capital and operating costs, are that they are more complex to build and maintain and therefore require skilled labour for operation and maintenance. There are many designs of each type, which are described in detail in publications in the Bibliography.
One type of dryer that has found application in many developing countries is the cabinet dryer (Figure 43), which is successfully used for drying herbs, herbal teas and spices and is also suitable for fruits and vegetables. In general a drying area of 1m2 is needed for 2-6 kg of raw materials, depending on the type of food (6 kg of chopped fruits need 1m2 whereas a product like shredded cabbage is less dense and can only be stacked at around 2 kg/m). These figures allow calculation of the size of the dryer that is needed for a given weight of food to be dried per day.
This range of products includes juices, squashes, sauces, pickles and chutneys. For liquid products, juice or pulp can be extracted from fruits or vegetables in a number of ways, depending on the hardness of the raw material. Soft fruits and vegetables, such as berries, tomatoes, grapes etc. can be processed by pressing, using a fruit press or using a juicer attachment to a food processor (Figure 44). Citrus fruits are usually reamed (Figure 45) to extract the juice without the bitter pith or skin.
Passion fruit or tomato and harder fruits, such as apple, pineapple etc. are peeled and then pulped using a liquidiser, or at large scales of operation using a pulper-finisher (Figure 16), which separates skins and seeds. Steamers, such as those used for blanching, can also be used to 'dissolve' some types of cut soft fruits such as melon and pawpaw. When a clear juice is required it is necessary to filter it through a fine muslin cloth or stainless steel juice strainers.
Figure 43.- A batch fuel fired dryer
(Courtesy of Midway Technology)
Figure 44. - Small juice extractor, fitted to a food processor
(Courtesy of Midway Technology)
The majority of products require heating to either pasteurise or concentrate them. In all cases a stainless steel boiling pan is needed. These are expensive to buy and in many countries local fabrication is difficult because the skills and facilities for welding stainless steel are not readily available. However, there are few alternatives and a producer should regard this expenditure as a necessary investment to be able to produce a high quality product. In some cases, such as squash production, it is possible reduce the capital investment by heating syrup to boiling in a large pan made from cheaper aluminium and then mixing it with juice in a smaller stainless steel pan for a final short heating to achieve the required pasteurisation conditions.
There are two types of boiling pans available, depending on the scale of operation: at smaller scales of operation, a simple stainless steel pan can be placed directly over the heat source. At larger scales of production, an indirectly heated, or 'double jacketed' pan (Figure 18) can be used. Steam is produced by a boiler and fed into the space between the outer jacket and inner pan to give more uniform heating and therefore avoid localised burning of the product. This may be particularly important when heating viscous products such as sauces, jams, chutneys etc., which are more likely to stick to a simple pan and burn onto it. This would not only reduce the quality of the product but also significantly slow down production while the pan is cleaned between batches.
Figure 45. - A small scale electric citrus reamer
The most appropriate type of heat source depends on the cost and availability of different fuels where the production is located. In general, gas or electricity are the preferred options because there is no risk of contamination of the product by un-burned fuel or combustion gases. A comparison of the advantages and limitations of different fuels is shown in Table 24, but the final decision on which fuel to use is likely to be based on considerations of finance and availability during the feasibility study. The majority of products also require equipment for monitoring and control, particularly those in which the concentration of sugar, salt or acid is important for preservation. This is discussed in more detail in Section 2.7.2.
In addition to the equipment required to prepare juices for fermentation, this group of products require more specialised equipment for fermentation and distillation. Wines are fermented in either food grade plastic drums or large glass vessels, which have a narrow opening into which an air lock (Figure 24) can be fitted. An alcohol hydrometer (similar in appearance to the brine hydrometer in Figure 55) is not essential, but it is a useful aid to standardising the alcohol content of the products.
It is possible to make vinegar by simply exposing wine to the air, but yields are low and there is a high risk of spoilage. A commercially made vinegar fermenter is too expensive for most producers, but if expertise is available, a locally produced fermenter having a traditional design can be made (Section 2.2.10).
Commercially produced distillation apparatus is also expensive to buy and locally made alternatives are likely to be preferred by small scale producers. With experience and adequate control over heating, these can produce acceptable products. They should be fitted with a pressure safety device, such as a long pipe that is submerged below the level of the liquor and exits the heating vessel to a height of at least 1.5 metres. If the outlet to the still becomes blocked, this will prevent the pressure rising to the point where the still would explode.
All types of plastic film, with the exception of un-coated cellulose, can be sealed using a heat sealer (Figure 46). The differences in the types of sealer are due to the width of the heated bar or wire and the level of control over temperature and time of heating. For dried and liquid foods a relatively wide seal (e.g. 3-5 mm) is required and bar-type sealers are therefore preferable to wire-types. The sealer should also have a thermostat to adjust the sealing temperature, and an adjustable timer to control the time of heating. Care should be taken to ensure that there is no product dust on the inside of the package where the seal is to be made as this will prevent proper sealing.
Table 24. - A comparison of different sources of heat for processing
|
Criteria |
Electricity |
Gas |
Liquid fuels |
Solid fuels |
|
Energy per unit weight or volumea |
not applicable |
low |
high |
moderate to high |
|
Cost per unit of energyb |
moderate to high |
high |
moderate to high |
low |
|
Heating equipment cost |
low |
low |
high |
high |
|
Efficiency of heating |
high |
moderate to high |
moderate to low |
low |
|
Flexibility of use |
high |
high |
low |
low |
|
Fire or explosion hazard |
low |
high |
low |
low |
|
Risk of contaminating food |
low |
low |
high |
high |
|
Labour and handling cost |
low |
low |
low |
high |
a Heating values (in kJ/kg x 103) for gas = 1.17-4.78, for oil = 8.6-9.3, for coal = 5.26-6.7, for wood = 3.8-5.26.b depending on presence of national hydro-electric schemes, coal mines or afforestation projects
(From: Food Processing Technology, by Fellows)
Solid products, such as pickles and chutneys are usually filled by hand using scoops or ladles into jars, plastic pots or bags. This is a time-consuming operation, which may require a large staff input (e.g. Figure 33). However, in most small scale operations, this is the only realistic option because mechanical fillers for these types of product are prohibitively expensive and usually operate at too high a throughput.
Figure 46. - A heat sealer for sealing plastic films
Although liquid products can also be filled by hand using jugs or ladles, in contrast to solid products there are a number of small liquid fillers available, which are affordable by many small scale producers. Examples of these include gravity fillers, made by fitting gate valves to stainless steel or food grade plastic tanks (note: domestic taps should not be used because they are too difficult to clean properly). Other designs include volumetric fillers and dispensers, in which a measured amount of liquid is filled into each container by the action of a piston (Figure 47). Small machines are available to seal jars, bottles, cans, plastic pots and films. Details of the various designs and suppliers are given in publications in the Bibliography.
There is a very wide range of packaging materials that can be used for foods and these cannot be described in detail in a book of this size. Publications in the Bibliography describe some types of packaging in more detail, but entrepreneurs should contact packaging manufacturers or their agents for a complete list of the available types. The following is a brief description of some of the more important points concerning the most widely available types of packaging materials in most developing countries. Additional information that relates to specific products is given in Sections 2.2.3 and 2.5.4. Marketing aspects are described in Section 2.8.3.
Figure 47. - A volumetric piston filler for liquid products
Jars and bottles are available in countries that have a glass-works, or have access to an overland supply from a neighbouring country. Because of their heavy weight, high bulk and fragility, glass containers are expensive to transport long distances and are frequently not available to producers in developing countries. Where they are available, they are usually re-used and great care is needed to ensure that they are properly cleaned. New and re-used containers should be sealed with new caps, lids or corks in order to obtain an adequate seal. The most common jar lids are now TOTO type (twist on, twist off), although the 'Omnia' type is still found in many countries. Bottles may be sealed using ROPP (roll on pilfer-proof) caps or corks. Cans are not widely used in small scale processing for the reasons described in Section 2.2.2.
Plastic pots and bottles are suitable for some types of foods and they are becoming increasingly common as a result of their lower production and distribution costs. Pots can be either heat sealed with a foil lid or with a snap-on plastic lid. The most common types of plastic film in developing countries are polythene and polypropylene, although increasingly there are agents who can supply more sophisticated (and expensive) imported laminates (Table 25).
Small laminated plastic/foil/cardboard cartons for UHT juices are appearing in many countries, but these are usually imported under licence to large scale juice manufacturers and are not available to small scale processors. Additionally, the UHT technology is not suitable for small scale production. Other cardboard and paper packaging is more widely available and can usually be printed by local print companies.
Other, more traditional types of packaging such as leaves, jute, hessian, wood and pottery are not usually able to convey an image of 'modem' or hygienic products and except for some niche export or tourist markets, these are not widely used (see also Section 2.8.3).
The properties of some of the more commonly used packaging films are shown in Table 25.
Table 25. - Properties of selected packaging materials
|
Type of film |
Thickness (m m) |
Yield (m2kg-1) |
Moisture transmissiona |
Oxygen transmissionb |
Strengthc |
Light transmission (%) |
Sealing temperature (°C) | |
|
Cellulose | ||||||||
|
|
- uncoated metallized |
21-40 |
18-30 |
800-1500 |
8-10 |
33 |
TP |
N/A |
|
|
- PVdC coated |
21-42 |
17-31 |
4-5 |
2-3 |
28-60 |
0 |
90-130 |
|
Polyethylene | ||||||||
|
|
- low density |
25-200 |
5-43 |
14-19 |
8000 |
7-16 |
- |
121-170 |
|
|
- stretch wrap |
17-38 |
- |
- |
- |
- |
- |
N/A |
|
|
- high density |
350-1000 |
11-43 |
4-6 |
500-2000 |
24-61 |
- |
135-170 |
|
Polypropylene | ||||||||
|
|
- biaxially oriented |
20-40 |
27-55 |
3-7 |
2000 |
118-260 |
TP |
117-124 |
|
|
- PVdC coated |
18-34 |
30-53 |
4-8 |
- |
- |
TP |
120-145 |
|
|
- metallized |
20-30 |
36-55 |
1 |
- |
215 |
0.5 |
120-145 |
|
Polyester | ||||||||
|
|
- plain |
12-23 |
31-59 |
20-40 |
53-110 |
- |
87 |
100-200 |
|
|
- metallized |
- |
- |
0.8-2 |
0.5-1.5 |
- |
0 |
100-200 |
|
Polyvinylidene chloride |
10-50 |
17-35 |
1-4 |
2 |
120-130 |
90 |
100-160 | |
a Moisture vapour transmission rate (ml m-2 per 24 hours) measured at 38°C and 90% relative humidityb Oxygen transmission rate (ml m-2 per 24 hours) measured at 25°C and 45% relative humidity
c Tensile strength (MN m-2) in machine direction.
PVdC - Polyvinylidene Chloride
TP - transparent,
N/A - not applicable(From: Food Processing Technology, by Fellows)
