Harry Lovell lifts the lid on the progressive development of canning technology The news that the National Packaging Covenant in Australia will now include overarching requirements in packaging waste recovery will have a profound effect on the industry which will affect the various material sectors in different ways.
The metals sector, aluminium and steel, already has an excellent track record on which to build. We often overlook the continuing development which takes place and this caused me to reflect on the canning industry.
Over the last 50 years we have seen a progressive development in canning technology. In the 1950s we saw the introduction of double reduced tinplate, resulting in significant weight savings without sacrificing the strength of the can.
Parallel developments took place with differential electrolytic tin plating, which was a significant move away from hot dipped tinplate with its heavy coatings of tin.
In the late 1960s we saw a shift towards the use of black plate as a reflection of the concern regarding the availability of raw tin. The next stage was the replacement of the folded side seam with a welded seam. Under the Ultimate Can program, tin can walls were targeted to become 0.22mm in thickness and later to become even thinner, down to 0.08mm. In 1994 polymer coated tin free steel (Ferrolite) came on to the market.
The manufacture of cans however had also progressed with the introduction of the Drawn-Redraw and Drawn Wall and Ironed processes resulting in two piece cans. These however did not replace the three piece can used for food, except in the smaller sizes due to the inability of the two piece can to withstand the pressures used in retorting systems. Anecdotal evidence suggests that attempts were made to seal these cans with an internal positive pressure prior to processing in order to avoid paneling, but were not successful.
Amongst the more recent developments has been the shift to smaller seams, resulting in a reduction in material usage. Originally developed by Carnaud Metal Box in 1981 and for food cans in 1992, the Miniseam is now well established overseas. Another system termed the Microseam by the US-based Microseam Engineering Systems has resulted in claims of a reduction of 10 per cent in terms of costs.
An interesting but short lived can development which came onto the market in the early 1960s was the Harvey Duo-can. This can contained a welded panel midway in the can body which was filled, first from one end and closed. Then the can was inverted and filled from the other end. One end contained rice and the other a meat based product (beef, chicken etc), eg curried beef.
Theirs was a range of meat products all partnered with rice under the Harvey label, produced and marketed by Pickering and West (owned by Fisons Foods). Unfortunately, whilst the product was very successful, it was limited by the fact that only rice was found to be compatible in processing terms. One alternative inspired by marketing was strawberries and cream which, needless to say, did not make the supermarket shelves! The can was expensive to make and eventually fell victim to cost.
Subsequently, whilst the exercise was not repeated, the concept was not entirely lost and two cans in a single sleeve with two meal components were produced, but did not have the cache in the marketplace.
Processing developments also took place. Notable amongst these was the Dole canning system. This system sterilised the cans with steam and these were then filled with aseptically processed product. The system could be used for drums up to 208L capacity. The Dole line was awesome due to the heat produced by the steam sterilising process, but nevertheless it paved the way for aseptic processing.
Another notable development was the concept of applying direct heat to the can in an environment at normal atmospheric pressure. Developed by the French, the Stériflamme plant enabled gas flames bearing directly on the surface of the can, whilst it rolled along a series of tracks. The gases used included propane, methane and butane. Cooling was carried out by a series of water sprays. Heat penetration was good with the product sterilised before complete cooking. It was used for carrots, French beans, mushrooms and salsifis. Cans up to 10cm in diameter could be processed.
CSIRO also produced a plant based on the same principles called the Tarax. One of the requirements of flame sterilisation was that the contents served to encourage heat distribution by agitation in the liquid in which they were immersed. Some attempts were made with hard pack mushrooms and had disastrous consequences!
The most recent developments have been in the shaping and profiling of cans using hydrostatic pressure.
The dominance of the tin can however has been challenged by the retortable pouch originally referred to as a plastic can. Two rigid packs seeking to emulate the can have appeared. The first of these was the Letpack, proclaimed as the "first retortable plastics can". Introduced in the 80s by �kerland & Rausing, it was made of an injection moulded polypropylene/aluminium foil laminate. It could be filled on existing filling lines suitably modified to accept the rectangular format.
A promised development was for a version termed the Micropak, which was to be suitable for microwave heating. The problem with the Letpak was the slow filling speed which did not make it economically viable. Nevertheless, technically it was sound.
The next major contender was the Stepcan. A clear PET plastics container formed by the Stretch Tube Extrusion Process (metal; box patent) which was sealed at both ends by conventionally double seamed metal ends. Packs were claimed to offer a shelf life of over six months, depending on the product.
The first stage was to pack products, which were syrup or fruit juice based with a further development into retort processing. Marketed in the late 80s by Marks and Spencer’s, it enjoyed a brief period of success, but in the end proved too costly.
The can has seen off many challenges and remains a solid performer on the supermarket shelves. Its long history and metal construction has consolidated its position in consumers, minds and no doubt its ease of recovery for recycling will ensure its position in the market for years to come.
What is clear, however, is that metal, like many other packaging material, has been in continuous development, making strides in material reduction and innovation which have simply been taken for granted? That factor needs to be changed.
