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12. Packaging


Functions of packaging
Constraints on adequate packaging
Packaging materials
Properties of packaging materials

The main aims of packaging are to keep the food in good condition until it is sold and consumed, and to encourage customers to purchase the product. Correct packaging is essential to achieve both these objectives. The importance of packaging can be summarized as follows.

· If adequately packaged, the shelf-life of local surpluses of food may be extended, and this allows the food to be distributed to other areas. In doing so, consumers are given more choice in terms of food available, food resources can be more equitably distributed, and rural producers may be able to generate income from surplus produce.

· Correct packaging prevents any wastage (such as leakage or deterioration) which may occur during transportation and distribution.

· Good packaging and presentation encourages consumers to buy products.

Solutions to packaging problems differ from region to region. Variations are the result of factors such as economics, the availability or access to packaging materials, infrastructure, distribution systems, climatic conditions and consumer habits. In many parts of the world, foods are wrapped in re-used newsprint, animal skins, rushes, or reeds. These materials are normally used for foods which are consumed soon after purchase (e.g. snack foods and bakery goods) and which therefore need little protection, or for foods such as flour and sugar which are likely to be transferred into storage vessels in the home.

Foods with a longer expected shelf-life have different needs and may require more sophisticated packaging to protect them against air, light, moisture, and bacteria.

Functions of packaging

Packaging should provide the correct environmental conditions for food starting from the time food is packed through to its consumption. A good package should therefore perform the following functions:

· it should provide a barrier against dirt and other contaminants thus keeping the product clean

· it should prevent losses. For example, packages should be securely closed to prevent leakage

· it should protect food against physical and chemical damage. For example the harmful effects of air, light, insects, and rodents. Each product will have its own needs

· the package design should provide protection and convenience in handling and transport during distribution and marketing

· it should help the customers to identify the food and instruct them how to use it correctly

· it should persuade the consumer to purchase the food.

Constraints on adequate packaging

Inadequate packaging may be the result of:

· a lack of knowledge of the materials and/or the requirements for packaging different foods. Each product has its own characteristics and packaging requirements vary

· in many countries the choice of packaging materials may be limited. For those that are available, supplies are often situated in urban areas and this may cause problems for the rural producer in terms of transportation and often in negotiating with suppliers

· packaging can represent a large part of the total cost of a processed food. This may be in part the result of the higher unit cost when small quantities are ordered for small-scale production.

Packaging materials

In many developing countries the most commonly used packaging materials include:

· leaves
· vegetable fibres
· wood
· papers, newsprint
· earthenware
· glass
· plastics
· metals

Leaves

Banana or plantain leaves are often used for wrapping certain types of food (e.g. steamed doughs and confectionery). Corn husk is used to wrap corn paste or unrefined block sugar, and cooked foods of all types are wrapped in leaves (e.g. vine leaves, bamboo leaves). They are an excellent solution for the problem of how to package products that are consumed soon after purchase as they are cheap and readily available. They do not however protect the food against moisture, oxygen, odours or micro-organisms, and are therefore not suitable for long-term storage.

Stuffing leaves with food

Vegetable fibres

These include bamboo, banana, coconut, cotton, jute, raffia, sisal, and yucca. These natural materials are converted into yarn, string or cord which will form the packaging material. These materials are very flexible, have some resistance to tearing, and are lightweight for handling and transportation. Being of vegetable origin, all of these materials are biodegradable and to some extent re-usable.

As with leaves, vegetable fibres do not provide protection to food which has a long shelf-life since they offer no protection against moisture pick-up, micro-organisms, or insects and rodents.

Wood

Wooden shipping containers have traditionally been used for a wide range of solid and liquid foods including fruits, vegetables, tea and beer. Wood offers good protection, good stacking characteristics, strength and rigidity. Plastic containers, however, have a lower cost and have largely replaced wood in many applications. The use of wood continues for some wines and spirits because the transfer of flavour compounds from the wooden barrels improves the quality of the product.

Peri mula

Vegetable fibre basket

Wooden crate

Paper

Paper is an inexpensive packaging material and can be made from a wide range of materials, including rice husks, banana leaves and wood pulps. It is however highly absorptive, fairly easily torn, and offers no barrier to water or gases.

Some of these constraints can be overcome by treating the paper in various ways. A well-known method is to dip the paper in wax, or alternatively impregnate it with varnish or resin. Paper can also be strengthened by combining it with hessian cloth, cardboard or polythene.

The degree of paper re-use will depend on its former use, and therefore paper that is dirty or stained should be rejected. Newsprint should be used only as a outer wrapper and not be allowed to come into direct contact with food, as the ink used is toxic.

Earthenware

Earthenware pots are used worldwide for storing liquids and solid foods such as curd, yoghurt, beer, dried food, and honey. Corks, wooden lids, leaves, wax, plastic sheets, or combinations of these are used to seal the pots. Unglazed earthenware is porous and is suitable for products that need cooling such as curd. Glazed pots are needed for storing liquids (oils, wines) as they are light-proof, and if clean, restrict the entry and growth of micro-organisms, insects and rodents.

Curd pots

Glass

A display of products in glass bottles/jars

Glass has many properties which make it a popular choice as a packaging material:

· glass is able to withstand heat treatments such as pasteurization and sterilization

· it does not react with food

· it is rigid and protects the food from crushing and bruising

· it is impervious to moisture, gases, odours and microorganisms

· it is re-usable, re-sealable and recyclable

· it is transparent, allowing products to be displayed. Coloured glass may be used either to protect the food from light or to attract customers.

Despite its many advantages, glass does have certain constraints:

· glass is heavier than many other packaging materials and this may lead to higher transport costs

· it is easy to fracture, scratch and break if heated or cooled too quickly

· potentially serious hazards may arise from glass splinters or fragments in the food.

Preparation of glass containers

A good product packaged in a dirty container will soon deteriorate and therefore the following stages are recommended:

Inspection. This stage applies equally to both new and reused containers. Any chipped, cracked, or heavily soiled containers must be rejected. Containers which have been used to store strong smelling substances such as kerosene should be rejected.

Washing. It is preferable that detergent and bleach are used for cleaning. However, if these are not available, soap or ashes may be used. Simple hand-held brushes can be used to aid the cleaning process on a small scale. For higher rates of production, powered washers are available (see Section 02.0).

Rinsing. Thorough rinsing of containers is essential. A simple rinsing system, illustrated below, involves a series of spigots set into a length of pipe which act as rinse sprays.

Sterilization. It is strongly recommended that prior to filling, glass containers are heat sterilized. Sterilization can be achieved very simply by holding the open neck of the container over the spout of a kettle containing boiling water. Containers can be inverted over a steam pipe which is supplied from a water boiler (see illustration). The vertical pipe is vital as it acts as a safety valve. Alternatively, glass containers can be boiled in water for ten minutes to sterilize them (see diagram below).

Bottle rinser

Sterilization of bottles

Sealing and capping

Bottles. Suitable machines for sealing bottles can be produced locally. There are two types of cap commonly used: those that thread onto the bottle neck, and crown caps which are pushed on under pressure. Simple low cost crown capping machines are available (see Section 47.2).

Jars. The sealer shown below is an efficient method for sealing jam jars with push-on lids (compared to domestic methods of using plastic and rubber bands). If bottle or jar necks are not always regular in size, a flexible plastic material allows the sealer to be fitted on different sizes of container. For details of other pieces of sealing equipment see section 47.1.

Cooling

Many products are filled into glass containers while they are hot and then need to be cooled quickly. To achieve this the containers can be stacked and cooled by circulating air. Alternatively, the cooler shown below can be used for both glass and metal containers.

Jam jar sealer

A shallow bath is constructed and the newly filled containers enter at point A, and roll slowly down the sloping bottom to B, where they are removed. Cold water enters at B and overflows as hot water at A. A weak solution of bleach is allowed to drip into the end, B, thus ensuring that the cooling water is chlorinated.

Bottle cooling system

A slightly different method is used for jars of jam. In order to set to a smooth gel, the jam jar must be allowed to cool standing in a vertical position. The filled jars are loaded into 'carriages' and then placed in the cooling trough, as for the bottles.

Plastics

The use of various plastics for containing and wrapping food depends on what is available in a particular country. Plastics are extremely useful as they can be made in either soft or hard forms, as sheets or containers, and with different thickness, light resistance, and flexibility. The filling and sealing of plastic containers is similar to glass containers.

Flexible films are the most common form of plastic. Generally, flexible films have the following properties:

· their cost is relatively low

· they have good barrier properties against moisture and gases

· they are heat sealable to prevent leakage of contents

· they have wet and dry strength

· they are easy to handle and convenient for the manufacturer, retailer, and consumer

· they add little weight to the product

· they fit closely to the shape of the product, thereby wasting little space during storage and distribution.

Flexible films include cellulose, polypropylene, and polythene.

Material

Properties

Cellulose

Plain cellulose is a glossy transparent film which is odourless and tasteless. It is tough and sharp resistant, although it tears easily. However it is not heat sealable and the dimensions and the permeability of the film vary with changes in humidity. It is used for foods that do not require a complete moisture or gas barrier.

Polythene
Low-density polythene

Heat sealable, inert, odour-free, and shrinks when heated. It is a good moisture barrier, but has a relatively high gas permeability, sensitivity to oils, and poor odour resistance. It is less expensive than most films and is therefore widely used.

High-density polythene

Stronger, thicker, less flexible, and more brittle than low-density polythene. It has lower permeability to gases and moisture. It has a higher softening temperature (121°C) and can therefore be heat sterilized.

Polypropylene

Polypropylene is a clear glossy film with a high strength, and is puncture resistant. It has low permeability to moisture, gases, and odours, which is not affected by changes in humidity. It stretches, although less than polythene. It has good resistance to oil, and therefore can be used successfully for packaging oily products.

Coated films

Coated films are coated with other polymers or aluminium to improve the barrier properties or to enable them to be heat sealed.

Laminated films

Laminated films are two or more films glued together. Lamination improves the appearance, the barrier properties, or the mechanical strength of a package. Aluminium foil is widely used in laminated films where low gas, water vapour, odour, or light transmission is required.

Sealing with a candle and hacksaw blade

Sealing with a powered sealer

Sealing techniques

Sachets or pouches made from flexible films can be sealed by folding the edge of the film over the teeth of a hacksaw blade (a used hacksaw blade works better) and passing the folded edge through a flame. The result does not look as good as when a heat sealer is used, but practice can improve the appearance of the bag.

Powered sealers can be operated by placing the plastic between two heated bars (the bars are coated with a special tape to prevent the plastic from melting). These machines are available commercially and usually designed to use electricity (see section 47.1) but they can be reproduced locally and modified to use alternative energy sources.

It is possible on a small scale to seal foil lids onto plastic pots. This can be done by purchasing a specially-designed heat sealer (see section 47.1), or alternatively, a domestic iron can be used.

Metal

Metal cans have a number of advantages over other types of containers:

· they provide total protection of the contents
· they are tamperproof
· they are convenient for presentation.

Constraints associated with use of metal cans include:

· they are heavier than other materials, except glass, and therefore have higher transport costs

· the heat treatment associated with the use of metal cans is not suitable for small-scale production (see sterilization).

Sealing techniques

Cans are sealed with a double seam and there are small scale seaming machines available to do this (see section 05.2).

The table opposite summarizes properties of a range of packaging materials.

Properties of packaging materials

Packaging materials such as glass are often made in developing countries but materials such as plastic film are more commonly imported from multinational packaging manufacturers. Most multinationals have a retail agent situated in developing countries and contact addresses can be found in local business directories.

Further information regarding suppliers and local costs of materials can be obtained from local packaging institutes; again these can be located through business directories.

Resistance to these factors

Type of packaging

Puncture crush etc

Sunlight

Air

Water

Heat

Odour

Insects

Rodents

Micro-organisms

Metal cans

*

*

*

*

#

*

*

*

*

Glass (bottle jar)

*

Coloured

*

*

*

*

*

*

*

Paper bag


*





#



Cardboard

*

*



#


#



Wood (box)

*

*



*


#

#


Pottery (sealed lid)

*

*

*

*

*

*

*

*

*

Foil


*


#

#

*

#



Plastic tub sealed

*

*


*

#

*

*

#

*

Cellulose uncoated



*

*


*

#



Cellulose coated



*

*


*

*


*

Polyethylene










Low-density



#

*


#

#


*

Stretch wrap




*






Shrink wrap




*






High density



*

*


*

#


*

Polypropylene



*

*


*

#


*

Polyester










Plain



*

*


*

*


*

Metallized

*

*

*

*

*

*

#


*

* = good protection
# = some protection

 


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