Steel and tin cans

[4] The tin canning process was conceived by the Frenchman Philippe de Girard, who had British merchant Peter Durand patent the idea in 1810.

[5][6] The canning concept was based on experimental food preservation work in glass containers the year before by the French inventor Nicholas Appert.

Durand did not pursue food canning, but, in 1812, sold his patent to two Englishmen, Bryan Donkin and John Hall, who refined the process and product, and set up the world's first commercial canning factory on Southwark Park Road, London.

[9] Most cans are right circular cylinders with identical and parallel round tops and bottoms with vertical sides.

However, in cans for small volumes or particularly-shaped contents, the top and bottom may be rounded-corner rectangles or ovals.

[12] In the mid-20th century, a few milk products were packaged in nearly rimless cans, reflecting different construction; in this case, one flat surface had a hole (for filling the nearly complete can) that was sealed after filling with a quickly solidifying drop of molten solder.

Concern arose that the milk contained unsafe levels of lead leached from this solder plug.

Steel cans are stronger than cartons or plastic, and less fragile than glass, protecting the product in transit and preventing leakage or spillage, while also reducing the need for secondary packaging.

[15] Food and drink packed in steel cans has equivalent vitamin content to freshly prepared, without needing preserving agents.

[15] Steel cans also extend the product's shelf-life, allowing longer sell-by and use-by dates and reducing waste.

[13] As an ambient packaging medium, steel cans do not require cooling in the supply chain, simplifying logistics and storage, and saving energy and cost.

[13] At the same time, steel's relatively high thermal conductivity means canned drinks chill much more rapidly and easily than those in glass or plastic bottles.

Nausea, vomiting, and diarrhea have been reported after ingesting canned food containing 200 mg/kg of tin.

[20] A 2002 study showed that 99.5% of 1200 tested cans contained below the UK regulatory limit of 200 mg/kg of tin, an improvement over most previous studies largely attributed to the increased use of fully lacquered cans for acidic foods, and concluded that the results do not raise any long term food safety concerns for consumers.

[40] As of August 2008[update], Health Canada's Food Directorate concluded that "the current dietary exposure to BPA through food packaging uses is not expected to pose a health risk to the general population, including newborns and infants".

[41] In modern times, the majority of food cans in the UK[42] have been lined with a plastic coating containing bisphenol A (BPA).

[43] A 2016 market, survey using Fourier-transform infrared spectrums to identify materials, found BPA and other substances known to have health harms were common in food can linings in the US.

[44] A can traditionally has a printed label glued to the outside of the curved surface, indicating its contents.

The smaller half sized can holds roughly 200 g, typically varying between 170 g and 225 g. Rimmed three-piece can construction involves several stages; Double seam rims are crucial to the joining of the wall to a top or bottom surface.

Illustrations of this process can be found on pages 20–22 of the FAO Fisheries Technical Paper 285 "Manual on fish canning".

30% thinner and weigh 40% less than 30 years ago, reducing the amounts of raw materials and energy required to make them.

This allows the use of magnetic conveyor systems[49] to transfer empty cans through the filling and packing processes, increasing accuracy and reducing potential spillage and waste.

[51] The first cans were heavy-weight containers that required ingenuity to open, with instructions directing to use a hammer and chisel, during the war of 1812, British soldiers resorted to use of bayonets and knives.

After an introduction of much thinner cans in the 1850s, a specialized opener became possible, and were introduced in 1855 (Robert Yeates[52]) and 1858 (Ezra J. Warner).

The push-lever opener similar to the modern ones was introduced in 1860 ("Bull's Head"), cutting wheel invented in 1870 (William W. Lyman).

Until the mid-20th century, some sardine tins had solder-attached lids, and the twist-key worked by forcing the solder joint apart.

[54] An additional innovation developed specifically for food cans uses a tab that is bent slightly upwards, creating a larger surface area for easier finger access.

For instance some people use two tin cans to form a camp or survival stove to cook small meals.

[58] A steel can can be recycled again and again without loss of quality;[59] however, for the food grade steel it's required to remove tin from the scrap metal, which is done by way of electrochemistry: the tin is leached from a high pH solution at low negative voltage.

There is also the potential for higher global steel recycling rates as consumers become more aware of the benefits.