Part 3.1.5: Preserved foods

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Extending the viability of precious seasonal foodstuffs has a long history. It has helped communities to survive seasonal periods of food shortage. Today, the techniques of food preservation have evolved but they are no less important in conserving both the nutritional value of the food concerned and the investment of labour and energy.

Effective packaging is a key to successful food preservation and thanks to its unique combination of properties, aluminium foil can play a valuable role in enabling modern preservation and delivery systems.

Heat sterilisation using autoclaves has stood the test of time, with examples reported of food products lasting, in extreme cases, for years without refrigeration. Packaging materials have moved on from the traditional metal cans and glass jars, which are still in use, to light weight pouches, foil containers and laminated cartons. These now offer the same preservation performance with much less weight and transportation demands.

Essential properies

Barrier

Alufoil’s total barrier to light, gases and liquids is the principle reason for its use in sterilizable flexible laminates, and can help to extend the viable life of foods for many months, even years.

Heat conductivity

Aluminium is very conductive to heat. This can help minimise processing, chilling and reheating times. It also evens-out the temperature gradient within its contents, helping product quality. Slim format pouches and containers allow the heat to penetrate more quickly than cylindrical shapes.

Heat resistance

Aluminium foil dishes can be used through a very wide temperature range from well below blast-freezing to the extremes of autoclaving. There is no risk of cracking, melting, charring or burning.

Durability and strength

When stamped into a shaped dish, aluminium foil ‘work-hardens’ where it is shaped. Thickness, alloy, shape and temper can be selected to create exactly the performance characteristics required.

Decorative potential

Alufoil’s metallic finish plus compatibility with all printing methods provides designers with scope to create stunning graphic design and shelf presence.

Lightness and space economy

Economies in both transport and storage result from lightness, flat or reeled format of empty packs and, in the case of alufoil containers, their nesting shapes.

Sustainability

Alufoil packaging reduces spoilage of sensitive products and, thanks to its barrier function, saves energy and material resources. Also, aluminium containers can be repeatedly recycled without loss of quality and at a fraction of their original energy cost. They are suitable for both separate and multi-material collection systems according to national and local conditions. The energy content of alufoil laminates can also be recovered by thermal treatment.

A variety of shelf stable alufoil pack formats

Pouches and sachets

Retortable ‘stand-up’ pouches are now an everyday packaging format thanks to the perfection of coatings and laminates designed to resist the rigours of autoclave sterilisation. To guarantee the integrity of the product, an alufoil layer is essential for full protection against light and gases.
The thin laminate and slim format of the flexible pouch enables heat to penetrate quickly to the whole of the product and also to cool very quickly. This means less overcooked product than is inevitable with traditional cylindrical cans.

Sterilizable pouches are used in a variety of sizes and formats, saving space and resources. A typical example is the multi- portion catering pack of tuna. Formally packed in large canisters, the contents remain fresh until the last of the product is used. The flexible pack is easy to open and can be reclosed, excluding oxygen. Full or empty, the pouches occupy a minimum of storage space.

Flexible pouches can also be used for three dimensional products such as sausages or fish portions and will adopt the form of the contents, excluding oxygen before sterilisation.

High barrier lidding

Thanks to its heat and pressure resistance, a high barrier alufoil laminate lid can extend the life of an otherwise short life fresh product. Foil-lidded single or multi-compartment plastic dishes, for example give long life protection for baby foods, snack meals, soups and vegetables. Canned foods such as fish are now routinely packed using high barrier peelable alufoil lidding instead of heavy gauge ring-pulls – economy coupled with ease of use.

Alufoil containers

These represent a remarkable success story in food packaging. Originally used for small portion packs of patés and fruit conserves, sealed smoothwall containers are now used for all manner of ‘shelf stable’ foods. The outcome of close collaboration between container producers and the specialists in inks and coatings, the lidded alufoil dish provides an ideal combination of characteristics. It is compact, attractive in appearance, fully protective yet easy to open and use.

The lightness of the metal and the stacking format of the empty container offers space and handling economy during the filling processes. The aluminium finish can be enhanced with coloured lacquers and high quality multicolour printing. Development continues thanks to alloy ‘tailoring’, downgauging and digital printing techniques, so enabling shorter runs coupled with economy without loss of performance.

Foil lined cartons

Aseptic filling of foil lined drinks cartons has been a successful and routine technique for some years. Now, a system using flexible alufoil laminate material which will withstand sterilisation at up to 130°C and 100% humidity for more than 2 hours after filling is available. The aluminium foil barrier plays a key part in the new pack and permits a shelf life of up to two years. Opening is simple thanks to a perforated tear-off top seam. Cartons save space and resources before and after filling.