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The objective of the packing process is to use any products made of any materials of any nature for the containment, protection, handling, delivery and presentation of goods. Packaging may be applied to raw materials and to processed goods.
Filling is the process of putting the product in the package in a proper way.
Field of application
The majority of food products are packaged before they enter the distribution chain. In some cases packing is an integral part of the production process, which means that the packaged product is further processed. An example is the canning and bottling of foods and subsequent heat conservation.
Techniques, methods and equipment
Most products involve primary, secondary and tertiary packing processes throughout the manufacture and distribution chain.
In the European Parliament and Council Directive 94/62/EC, Article 3 outlines the definition of packaging as “all products made of any materials of any nature to be used for the containment, protection, handling, delivery and presentation of goods, from raw materials to processed goods, from the producer to the user or the consumer. Non-returnable items used for the same purposes shall also be considered to constitute packaging.” It then goes on to state that “Packaging consists only of:
- sales packaging or primary packaging, i.e. packaging conceived so as to constitute a sales unit to the final user or consumer at the point of purchase
- grouped packaging or secondary packaging, i.e. packaging conceived so as to constitute at the point of purchase, a grouping or a certain number of sales units whether the latter is sold as such to the final user or consumer or whether it serves only as a means to replenish the shelves at the point of sale; it can be removed from the produce without affecting its characteristics; and finally
- transport packaging or tertiary packaging, i.e. packaging conceived so as to facilitate the handling and transport of a number of sales units or grouped packaging in order to prevent physical handling and transport damage. Transport packaging does not include road, rail, ship or air containers”.
Primary packaging may be metal containers, glass bottles, jars, rigid and semi-rigid plastic tubs and containers, collapsible tubes, paperboard cartons, flexible plastic bags, sachets, paper bags, etc.
Secondary packaging involves methods such as crates, pallets (wooden and plastic), shrinkwrap, trays, boxes and wrap-around cartons.
a) Type of packing materials
Various types of packing materials can be distinguished:
Textiles and wood
Textile has poor barrier properties. Textile bags are still used to transport bulk products including grain, flour, sugar and salt. Wooden (shipping) containers have traditionally been used for a range of foods, such as fruits, vegetables, tea, wines, spirits and beer. These wooden containers were replaced a long time ago in some sectors (e.g. only plastic crates are now used for packaging beer) and are increasingly being replaced everywhere by plastic drums and crates.
Hermetically sealed, metal cans have high barrier properties and can withstand high and low temperatures. The materials used for metal cans are steel and aluminium, but they may also be coated with tin or lacquers to prevent interactions with the foods within the can. Metal cans are widely used for soft drinks and beer. They are also used for canning, sterilised foods (fruits, vegetables, condensed milk, meat products). Metal cans are recyclable. Aluminium foil is also widely used for the packaging of several types of food.
Glass has high barrier properties, is inert, and is suitable for heat and microwave processing. However, two disadvantages of glass use as in packaging are its weight and the risk of fracturing. Glass bottles and jars are widely used for milk, beer, wines and spirits, preserves, pastes and purées and also for canning foods and instant drinks. Glass bottles and jars are reusable and recyclable.
Rigid and semi-rigid plastic containers
Bottles, jars, cups, trays and tubs can be made from single or co-extruded polymers. The main properties are low weight, tough and unbreakable, easy to seal, reasonably high barrier properties and great chemical resistance. Several techniques are available for the production of these containers, such as thermoforming, blow moulding, injection blow moulding, extrusion blow moulding and stretch blow moulding. Typical materials used are PVC, PS (polystyrene), PP (polypropylene), XPP (expanded polypropylene – for thermoforming), HDPE (high-density polyethylene), PET (polyethylene terephthalate), polycarbonate, etc. The containers are often made on-site. Some of the containers are reusable, e.g. polycarbonate bottles for milk. Rigid and semi-rigid plastic containers are used for milk, soft drinks, dairy products, margarine
, dried foods, ice-cream, etc.
Flexible films are formed from non-fibrous plastic polymers, which are normally less than 0.25mm thick. Typical materials used for flexible films are PP, polyethylene (PE), PET, LDPE, HDPE, polysterene (PS), PVC, etc. In general flexible films are relatively cheap, they can be produced with a range of barrier properties, they are heat sealable, add little weight, can be laminated to paper, aluminium and other plastics and are easy to handle. Flexible films are used for packing a large range of both wet and dry food products.
Paper and board
Paper and board can be produced in many grades and many different forms. It is recyclable and biodegradable and can easily be combined with other materials. Laminated paperboard packs are used on a large scale for milk and fruit
juices. Paper and board are also extensively used for food packing, often as secondary packing.
b) Filling, bottling and canning
Methods and techniques for filling, bottling and canning
The filling of liquids, pastes, powders and particulate foods can usually be distinguished by the packaging medium and the food product. For example, the filling of milk and other drink in glass bottles is normally called bottling, whilst filling in metal cans and subsequent heat processing is normally called canning.
The requirements for filling are:
- accuracy to ensure that the required amount of product is packed
- hygiene, i.e. ensuring that the product is hygienically filled at the correct temperature to guarantee the highest possible quality and optimum shelf-life.
The selection of an appropriate filling technique depends on the nature of the product and the production rate required. The filling can be by volume, level or weight. Two examples using the different filling types are:
- Volumetric filling, applied for liquids, but also for a range of other products like pastes and powders. Most common is the piston filler.
- Weight filling, large particulate materials (e.g. confectionery, tablets, etc) are filled into containers using a photoelectric device, similar to a sorter to count individual pieces. Also multi-head weighers are in development which aim to be able to weigh different products simultaneously, prior to filling into the same container.
Containers need to be filled accurately without spillage and without contamination of the seal.
The filling of liquid foods like milk and fruit/vegetable juices can be categorised by the temperature of the food at the time of filling, e.g. hot, ambient or fresh cold filling, or as aseptic filling. The temperature ranges involved in the filling process are best illustrated by the hot filling and fresh cold filling processes. Hot filling is done at temperatures of up 95°C, in order to inactivate certain relevant micro-organisms, whilst many drink products are formulated with ingredients that do not need to be heat treated in order to be microbiologically safe and these are therefore fresh cold filled at between 0 to 5°C.
For aseptic packing, pre-sterilised (by e.g. hydrogen peroxide) containers are necessary, and the filling taking place in a sterile zone.
An important step in the packing process is the sealing of the container or packs. The maintenance of the food quality depends largely on adequate sealing of the packs. Seals are mostly the weakest part of the packs and also suffer more frequent faults during production, such as food trapped in a seal, incorrect sealing temperatures or incorrect can seamer settings. There is a large range of materials and techniques in use for sealing, including metal crowns, metal/plastic screw caps, metal ends and corks. Form-fill-sealing is now a well established new technique. In this process the container is formed and partly sealed, filled and then finally closed by full sealing.