The improvement of the steel by means of the covering of its surface with tin has allowed magnificent applications since it is known. However, it has to be paired closely with an important association, that of the can manufacturers / users of the same, who in turn should be the guides of the consumers. Both manufacturers and users have to have knowledge about the practical, but basic characteristics of tinplate that determine the physical and chemical stability of cans from the tinplate line to the customers of any product packaged and preserved in metal containers.
Only the reciprocal flow of information between can manufacturers and users will allow technical and economic progress, providing greater knowledge of the subject. Both should strive to inform consumers about how to use cans to enjoy foods preserved in their integrity and the use of industrial products.
In the late Middle Ages saw the tin plate. At first it was only used to make homemade utensils, almost as a raw material for a certain art. Above all it was the British who quickly developed the technique of “whitening” iron. At the dawn of the 19th century, the discovery of Appert revolutionized the use of this material. Thanks to his experimental genius, he developed his process of stabilizing food in sealed glass jars, by heat treatment. In 1810 he published his famous book “The book of all homes or the art of conserving all animal and vegetable substances for several years.”
This process required perfectly hermetic containers for their proper functioning. The British, and then the French, did not take long to realize that tinplate was the most adequate to satisfy the total hermeticism, due to the particular virtue of tin being able to weld on itself. By 1820, the first cans of food made of tinplate were made and proved reliable. The canned food industry was born, soon acquiring an accelerated evolution, especially in the United States during the Civil War. The First and Second World War brought in France and England an important development of metal containers for food, in order to provide the troops with a balanced diet on the battlefields.
It should be noted that the steel, companion and base of the tin, had benefited from considerable improvements in its chemical and mechanical qualities. Iron had become steel during the second half of the 19th century. The progress made a few years before the Second World War in the techniques of cold rolling gave the possibility of providing metal packaging to the packaging, not only in huge quantities and economically, but also high reliability.
Nowadays, the manufacture of tinplate and its use have become common, happily coexisting with technology and science. At a certain moment it was feared that the very high price of tin could cause its decline. This was the reason for the appearance, almost half a century ago of materials that replaced tinplate as was the TFS. These materials, although also based on steel laminates, have undoubtedly found massive applications in the present to make caps and inlaid containers. , but tinplate still has a priority use, difficult to replace.
This success is based on at least five essential functions of a package, namely: protection, conservation, transportability, capacity for transformation into units and support for messages and information. Tinplate satisfies these conditions to a high degree.
Tinplate containers incorporate the strength and strength of steel. The metal supports pressures and efforts of a high level. They resist very well the blows received during their transport and handling. The magnetic characteristics of the steel allow easy selection in recycling. It is also an excellent material for electric welding (as is the case of the lateral seam of three-piece bodies), it can be decorated and varnished easily and offers new possibilities for improvements such as the incorporation of “easy opening” type caps .
The duration of canned (shelf life) content of food packaged in cans is a great triumph. The tin plate allows the conservation for long periods of time thanks to its total impermeability and the hermeticism guaranteed by its closures. The tin container is perfectly adapted to sterilization treatments of different types, providing food with the final biological stability with which its organoleptic qualities, color, texture and flavor are retained. Steel is an excellent conductor of cold and heat. The use of metal containers ensures the reliability of different food preservation techniques, such as aseptic, vacuum packaging, controlled atmosphere preservation, etc. Metal containers retain their vacuum or internal pressure for years if necessary.
Sometimes tin containers are criticized for not always providing the necessary chemical stability, ie they show a certain tendency to corrosion. However, in relation to the annual number of cans that are filled in the world, this problem is negligible. It is a reality that, at the rate of production of packaging plants, a case of corrosion inevitably leads to a significant number of waste cans.
The difficulty often lies in establishing what is the origin of this phenomenon, can be the product, the constituent elements of the can or the same packaging process. Detailing these possible causes a little more, mention can be made of:
– The suitability of the tinplate used. There is no good or bad tinplate, but knowing how to choose the right one for each use. A correct choice of thickness and especially of tinning is essential.
– The use of organic protection – varnishes – suitable for the product to be contained.
– The characteristics of the contained product. The excessive presence of certain components can be decisive, such as nitrates – which cause a rapid breakdown – from agricultural fertilizers or the water used, certain pesticides or insecticides from the crop, etc.
– The presence of oxygen – air – in the packaging is the source of problems. It is found mainly in the “head space”, (gap between the product and the lid). Oxygen is the declared enemy of the can with regard to corrosion. It is also the enemy of certain organoleptic and nutritional values of the food (color, taste, oxidation, aging). There are three techniques or procedures to reduce the presence of oxygen inside a can, which are: a) Filling and hot closing. b) Closure with steam injection. Steam replaces air in free space. C) Vacuum closing.
– The process itself. The same container and the same product can give problems or not depending on the process used. Water treatment, used steam, handling of the container … are decisive factors to obtain adequate results.
– The storage conditions can also be decisive. Thermal jump, moisture level, air currents, quality of used packaging … are other important addends to be taken into account.
The detailed development of all these causes would be a very lengthy work that goes beyond the possibilities of this article, although we will return to some of these points in a concrete way in other works. There is a vast literature on the subject. If it can be said by way of summary that it is possible to achieve that the metal container acts as a chemically stable element during its useful life. For this reason, an ideal food preservation system remains after nearly two centuries of history.