A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), or can is a container made of thin metal, for distribution or storage of goods. Some cans are opened by removing the top panel with a can opener or other tool; others have covers removable by hand without a tool. Cans can store a broad variety of contents: food, beverages, oil, chemicals, etc. In a broad sense, any metal container is sometimes called a "tin can", even if it is made, for example, of aluminium.[1][2]
Steel cans were traditionally made of tinplate; the tin coating stopped the contents from rusting the steel. Tinned steel is still used, especially for fruit juices and pale canned fruit. Modern cans are often made from steel lined with transparent films made from assorted plastics, instead of tin. Early cans were often soldered with neurotoxic high-lead solders. High-lead solders were banned in the 1990s in the United States,[3] but smaller amounts of lead were still often present in both the solder used to seal cans and in the mostly-tin linings.
Cans are highly recyclable and around 65% of steel cans are recycled.[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. By 1813 they were producing their first tin canned goods for the Royal Navy. By 1820, tin canisters or cans were being used for gunpowder, seeds, and turpentine.
Early tin cans were sealed by soldering with a tin–lead alloy, which could lead to lead poisoning.[citation needed] Automated soldering machines started to arrive in 1870s The steel started to displace iron as a material for the cans at the very end of the 19th century. Locking side seam was invented by Max Ams in 1888, giving the rise to a "sanitary can" design, where the solder was found only on the outside of the can and never touched the food. The modern three-piece design dates back to 1904 (Sanitary Can Company of New York).[7]
In 1901 in the United States, the American Can Company was founded, at the time producing 90% of the tin cans in the United States.[8] It bought out the Sanitary Can Company of New York in 1908, and the three-piece design displaced all other cans by the early 1920s. The can saw very little change since then, although better technology brought 20% reduction in the use of steel, and 50% - in the use of tin[7] (the modern cans are 99.5% steel).[9]
Canned food in tin cans was already quite popular in various countries when technological advancements in the 1920s lowered the cost of the cans even further.[10]: 155–170, 265–280 In 1935, the first beer in metal cans was sold; it was an instant sales success.[10]: 155–170, 265–280 The production of these three-piece cans by the American Can Company stopped for World War II due to lack of material, after the war the first two-piece cans with no side seams and a cone top were introduced. The use of aluminum started in 1958 with Primo beer.[11]
About 600 different types of cans were used in the early 21st century, with the most popular being the three-piece design with side seam and two doble-seamed ends, followed by the two-piece construction with sides and bottom drawn as one piece.[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. Other contents may suit a can that is somewhat conical in shape.
Fabrication of most cans results in at least one rim—a narrow ring slightly larger than the outside diameter of the rest of the can. The flat surfaces of rimmed cans are recessed from the edge of any rim (toward the middle of the can) by about the width of the rim; the inside diameter of a rim, adjacent to this recessed surface, is slightly smaller than the inside diameter of the rest of the can.
Three-piece can construction results in top and bottom rims. In two-piece construction, one piece is a flat top and the other a deep-drawn cup-shaped piece that combines the (at least roughly) cylindrical wall and the round base. Transition between wall and base is usually gradual. Such cans have a single rim at the top. Some cans have a separate cover that slides onto the top or is hinged.
Two piece steel cans can be made by "drawing" to form the bottom and sides and adding an "end" at the top: these do not have side seams. Cans can be fabricated with separate slip-on, or friction fit covers and with covers attached by hinges. Various easy opening methods are available.[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.
A number of factors make steel cans ideal containers for beverages. 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.[13][14]
Steel and aluminium packaging offer complete protection against light, water and air, and metal cans without resealable closures are among the most tamper-evident of all packaging materials.[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.[16]
![Flip-top can[17] with hinged cover](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/Trevqrp.png/1280px-Trevqrp.png)
No cans currently in wide use are composed primarily or wholly of tin.[18] Until the second half of the 20th century, almost all cans were made of tinplate steel. The steel was cheap and structurally strong, but prone to rust; the tin coating prevented the wet food from corroding the steel. Corrosion-resistant coatings on almost all steel food cans are now made from plastic, not tin. Some manufacturers use Vitreous enamel, instead.[19][better source needed]
Tin is corrosion resistant, but acidic food like fruits and vegetables can corrode the tin layer. 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. The two non-compliant products were voluntarily recalled.[21]
Evidence of tin impurities can be indicated by color, as in the case of pears, but lack of color change does not guarantee that a food is not tainted with tin.[22]
Lead is harmful to health in any quantity, and more lead is more harmful than less lead. Infants and children are more severely affected, as lead harms brain development.[23]
In November 1991, US can manufacturers voluntarily eliminated lead seams in food cans. Imported food cans continued to include lead soldered seams.[24][19]
In 1995, the US FDA issued a rule prohibiting lead soldered food cans, including both domestic and imported food cans.[25][19] Unfortunately, the FDA did not give a definition of "lead solder", or a quantitative limit to permissible lead levels, and some solders and tin linings used on tin cans still contained significant amounts of lead. In 2017, quantitative limits were set, but they are high enough to permit intentionally adding lead, and the FDA measurements show measurable levels of lead in many US canned foods in the 2010s.[3][26]
Many metal food cans are lined with plastic, to prevent the food from corroding the can.[27] These linings can leach contaminants into the canned food.[28] Some of these contaminants are substances with known health harms, though whether they are ingested in canned food in levels sufficient to cause harms is not known.[29]
Among other substances, the plastic linings in food cans often contain bisphenol A (BPA).[30][31][32][33] Pregnant women who eat more canned food have higher levels of BPA in their urine.[34]
Other constituents in can linings, including newer BPA-free can linings, have also been identified as having known health harms.[35]
Bisphenol-A (BPA) is a controversial chemical compound present in commercially available tin can plastic linings[37] and transferred to canned food. The inside of the can is coated with an epoxy coating, in an attempt to prevent food or beverage from coming into contact with the metal. The longer food is in a can, and the warmer and more acidic it is, the more BPA leaches into it. In September 2010, Canada became the first country to declare BPA a toxic substance.[38][39] In the European Union and Canada, BPA use is banned in baby bottles. The FDA does not regulate BPA (see BPA controversy#Public health regulatory history in the United States). Several companies, like Campbell's Soup, announced plans to eliminate BPA from the linings of their cans,[37] but have not said which chemical they plan to replace it with. (See BPA controversy#Chemical manufacturers reactions to bans.)[citation needed]
In 2016, BPA was common in food can linings in Canada.[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". They also stated that, as some animal studies had shown effects from low levels of BPA, they were seeking to make BPA levels in food packaged for infants and newborns (especially formula). They also cited a WHO review.[41]
In modern times, the majority of food cans in the UK[42] have been lined with a plastic coating containing bisphenol A (BPA). The coating prevents acids and other substances from corroding the tin or aluminium of the can, but leaching of BPA into the cans contents was investigated as a potential health hazard. The UK Food Standards agency currently considers can-derived BPA levels to be acceptable, but is investigating its safe-level thresholds; it currently has a temporary threshold for BPS, as of 2024[update].[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. A similar survey done by food can manufacturers in 2020 found BPA only in some imported cans; it did not discuss potential harms from lining substances other than BPA.[44]
A can traditionally has a printed label glued to the outside of the curved surface, indicating its contents. Some labels contain additional information, such as recipes, on the reverse side. More recently labels are sometimes printed directly onto the metal before or after the metal sheet is formed into the individual cans.
Traditionally, labels were glued on with casein glue, which dissolved easily in hot water. Some other glues may make the label harder to remove for recycling.
Cans come in a variety of shapes and sizes. Walls are often stiffened with rib bulges, especially on larger cans, to help the can resist dents that can cause seams to split.
Can sizes in the United States have an assortment of designations and sizes. For example, size 7/8 contains one serving of half a cup with an estimated weight of 4 ounces; size 1 "picnic" has two or three servings totalling one and a quarter cups with an estimated weight of 101⁄2 ounces; size 303 has four servings totalling 2 cups weighing 151⁄2 ounces; and size 10 cans, most widely used by food services selling to cafeterias and restaurants, have twenty-five servings totalling 13 cups with an estimated weight of 1031⁄2 ounces (size of a roughly 3 pound coffee can). These are U.S. customary cups, not British Imperial standard.
In the United States, cook books sometimes reference cans by size. The Can Manufacturers Institute defines these sizes, expressing them in three-digit numbers, as measured in whole and sixteenths of an inch for the container's nominal outside dimensions: a 307 × 512 would thus measure 3 and 7/16" in diameter by 5 and 3/4" (12/16") in height. Older can numbers are often expressed as single digits, their contents being calculated for room-temperature water as approximately eleven ounces (#1 "picnic" can), twenty ounces (#2), thirty-two ounces (#3), fifty-eight ounces (#5), and one-hundred-ten ounces (#10 "coffee" can).[45]
In parts of the world using the metric system, tins are made in 250, 500, 750 ml (millilitre) and 1 L (litre) sizes (250 ml is approximately 1 cup or 8 ounces). Cans imported from the US often have odd sizes such as 3.8 L (1 US gallon), 1.9 L (1/2 US gallon), and 946 ml (2 US pints / 1 quart).
In the UK and Australia, cans are usually measured by net weight. A standard size tin can holds roughly 400 g; though the weight can vary between 385 g and 425 g depending on the density of the contents. The smaller half sized can holds roughly 200 g, typically varying between 170 g and 225 g.
![Camp stove fuel in "F-Style" can[17]](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Camp_fuel.jpg/1280px-Camp_fuel.jpg)
