Background of the Study
Tinplate is light gauge, cold reduced, low-carbon steel sheet or strip, coated on both sides with commercially pure tin. It combines in one material the strength and formability of steel and the corrosion resistance and good appearance of tin. Just under one third of the world’s total tin production goes into the manufacture of tinplate, for which food packaging is by far the largest of many diverse applications. Tinplate has been used for preserving food for well over a hundred years and today provides a robust form of packaging, allowing minimisation of headspace oxygen and sterilisation of the foodstuff within the hermetically sealed can, giving a long, safe, ambient shelf life with no, or minimal, use of preservatives. Altogether, about 25,000 million food cans are produced and filled in Europe per annum, about 20% of
these having plain internal (unlacquered) tin-coated steel bodies. Worldwide, the total for food packaging is approximately 80,000 million cans. Plain internal tinplate cans are used for specific food types, including tomatoes and other tomato-based products, white fruits and some vegetables (e.g. mushrooms, asparagus). They are used, in preference to lacquered cans, in situations where a small lacquer discontinuity (e.g. scratch) would result in concentrated
attack of the base steel (the small area of tin would quickly disappear) and could potentially lead to pinholing and microbial ingress. Additionally, the presence of a bare tin surface inside the can leads to protection of the natural flavour and appearance of the food, through oxidation of the tin surface in preference to oxidative degradation of the food. This process retains the quality attributes that consumers expect from these products throughout the long shelf life.