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Canning is a method of
food preservation Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
in which food is processed and sealed in an airtight container (
jar A jar is a rigid, cylindrical or slightly conical container, typically made of glass, ceramic, or plastic, with a wide mouth or opening that can be closed with a lid, screw cap, lug cap, cork stopper, roll-on cap, crimp-on cap, press-on c ...
s like
Mason jar A Mason jar, also known as a canning jar or fruit jar, is a glass jar used in home canning to preserve food. It was named after American tinsmith John Landis Mason, who patented it in 1858. The jar's mouth has a screw thread on its outer perime ...
s, and
steel and tin cans A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans re ...
). Canning provides a
shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
that typically ranges from one to five years, although under specific circumstances, it can be much longer. A freeze-dried canned product, such as canned dried
lentil The lentil (''Lens culinaris'' or ''Lens esculenta'') is an edible legume. It is an annual plant known for its lens-shaped seeds. It is about tall, and the seeds grow in pods, usually with two seeds in each. As a food crop, the largest pro ...
s, could last as long as 30 years in an edible state. In 1974, samples of canned food from the wreck of the ''
Bertrand Bertrand may refer to: Places * Bertrand, Missouri, US * Bertrand, Nebraska, US * Bertrand, New Brunswick, Canada * Bertrand Township, Michigan, US * Bertrand, Michigan * Bertrand, Virginia, US * Bertrand Creek, state of Washington * Saint-Bert ...
'', a steamboat that sank in the Missouri River in 1865, were tested by the
National Food Processors Association The Food Products Association (formerly the National Food Processors Association or NFPA) was the principal U.S. scientific and technical trade association representing the food processing industry until 2007. FPA was headquartered in Washington, ...
. Although appearance, smell, and vitamin content had deteriorated, there was no trace of microbial growth and the 109-year-old food was determined to be still safe to eat.


History and development


French origins

During the first years of the
Napoleonic Wars The Napoleonic Wars (1803–1815) were a series of major global conflicts pitting the French Empire and its allies, led by Napoleon I, against a fluctuating array of European states formed into various coalitions. It produced a period of Fren ...
, the French government offered a hefty cash award of 12,000 francs to any inventor who could devise a cheap and effective method of preserving large amounts of food. The larger armies of the period required increased and regular supplies of quality food. Limited food availability was among the factors limiting military campaigns to the summer and autumn months. In 1809,
Nicolas Appert Nicolas Appert (17 November 1749 – 1 June 1841) was the French inventor of airtight food preservation. Appert, known as the " father of Food Science", was a confectioner. Appert described his invention as a way "of conserving all kinds of food ...
, a French confectioner and brewer, observed that food cooked inside a jar did not spoil unless the seals leaked, and developed a method of sealing food in glass jars. Appert was awarded the prize in 1810 by Count Montelivert, a French minister of the interior. The reason for lack of spoilage was unknown at the time, since it would be another 50 years before
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
demonstrated the role of microbes in food spoilage. The French Army began experimenting with issuing canned foods to its soldiers, but the slow process of canning foods and the even slower development and transport stages prevented the army from shipping large amounts across the French Empire, and the war ended before the process was perfected. Following the end of the
Napoleonic Wars The Napoleonic Wars (1803–1815) were a series of major global conflicts pitting the French Empire and its allies, led by Napoleon I, against a fluctuating array of European states formed into various coalitions. It produced a period of Fren ...
, the canning process was gradually employed in other European countries and in the US.


In the United Kingdom

Based on Appert's methods of food preservation, the
tin can A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans re ...
process was allegedly developed by Frenchman
Philippe de Girard Philippe Henri de Girard (February 1, 1775 – August 26, 1845aged 70) was a French engineer and inventor of the first flax spinning frame in 1810, and the person after whom the town of Żyrardów in Poland was named. He was also the uncredited in ...
, who came to London and used British merchant Peter Durand as an agent to patent his own idea in 1810. Durand did not pursue food canning himself, selling his patent in 1811 to
Bryan Donkin Bryan Donkin FRS FRAS (22 March 1768 – 27 February 1855) developed the first paper making machine and created the world's first commercial canning factory. These were the basis for large industries that continue to flourish today. Bryan Do ...
and
John Hall John Hall may refer to: Academics * John Hall (NYU President) (fl. c. 1890), American academic * John A. Hall (born 1949), sociology professor at McGill University, Montreal * John F. Hall (born 1951), professor of classics at Brigham Young Unive ...
, who were in business as Donkin Hall and Gamble, of
Bermondsey Bermondsey () is a district in southeast London, part of the London Borough of Southwark, England, southeast of Charing Cross. To the west of Bermondsey lies Southwark, to the east Rotherhithe and Deptford, to the south Walworth and Peckham, a ...
. Bryan Donkin developed the process of packaging food in sealed airtight cans, made of tinned wrought iron. Initially, the canning process was slow and labour-intensive, as each large can had to be hand-made, and took up to six hours to cook, making canned food too expensive for ordinary people. The main market for the food at this stage was the
British Army The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurk ...
and
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
. By 1817, Donkin recorded that he had sold £3000 worth of canned meat in six months. In 1824, Sir
William Edward Parry Sir William Edward Parry (19 December 1790 – 8 July 1855) was an Royal Navy officer and explorer best known for his 1819–1820 expedition through the Parry Channel, probably the most successful in the long quest for the Northwest Pass ...
took canned beef and pea soup with him on his voyage to the Arctic in HMS Fury, during his search for a northwestern passage to India. In 1829, Admiral Sir James Ross also took canned food to the Arctic, as did Sir
John Franklin Sir John Franklin (16 April 1786 – 11 June 1847) was a British Royal Navy officer and Arctic explorer. After serving in wars against Napoleonic France and the United States, he led two expeditions into the Canadian Arctic and through ...
in 1845. Some of his stores were found by the search expedition led by Captain (later Admiral Sir)
Leopold McClintock Sir Francis Leopold McClintock (8 July 1819 – 17 November 1907) was an Irish explorer in the British Royal Navy, known for his discoveries in the Canadian Arctic Archipelago. He confirmed explorer John Rae's controversial report gather ...
in 1857. One of these cans was opened in 1939 and was edible and nutritious, though it was not analysed for contamination by the lead solder used in its manufacture.


In Europe

During the mid-19th century, canned food became a
status symbol A status symbol is a visible, external symbol of one's social position, an indicator of economic or social status. Many luxury goods are often considered status symbols. ''Status symbol'' is also a sociological term – as part of social and soci ...
among middle-class households in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, being something of a frivolous
novelty Novelty (derived from Latin word ''novus'' for "new") is the quality of being new, or following from that, of being striking, original or unusual. Novelty may be the shared experience of a new cultural phenomenon or the subjective perception of an ...
. Early methods of manufacture employed poisonous
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...
for sealing the cans. Studies in the 1980s attributed the lead from the cans as a factor in the disastrous outcome of the 1845
Franklin expedition Franklin's lost expedition was a failed British voyage of Arctic exploration led by Captain (Royal Navy), Captain Sir John Franklin that departed England in 1845 aboard two ships, and , and was assigned to traverse the last unnavigated sect ...
to chart and navigate the
Northwest Passage The Northwest Passage (NWP) is the sea route between the Atlantic and Pacific oceans through the Arctic Ocean, along the northern coast of North America via waterways through the Canadian Arctic Archipelago. The eastern route along the Arct ...
. However, studies in 2013 and 2016 suggested that lead poisoning was likely not a factor, and that the crew's ill health may, in fact, have been due to malnutrition – specifically zinc deficiency – possibly due to a lack of meat in their diet. Increasing mechanization of the canning process, coupled with a huge increase in urban populations across Europe, resulted in a rising demand for canned food. A number of inventions and improvements followed, and by the 1860s smaller machine-made steel cans were possible, and the time to cook food in sealed cans had been reduced from around six hours to thirty minutes.


In the United States

Canned food also began to spread beyond EuropeRobert Ayars established the first American canning factory in
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
in 1812, using improved tin-plated wrought-iron cans for preserving
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not al ...
s,
meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
s,
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
s and
vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...
s. Demand for canned food greatly increased during wars. Large-scale wars in the nineteenth century, such as the
Crimean War The Crimean War, , was fought from October 1853 to February 1856 between Russia and an ultimately victorious alliance of the Ottoman Empire, France, the United Kingdom and Piedmont-Sardinia. Geopolitical causes of the war included the de ...
,
American Civil War The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...
, and Franco-Prussian War, introduced increasing numbers of working-class men to canned food, and allowed canning companies to expand their businesses to meet military demands for non-perishable food, enabling companies to manufacture in bulk and sell to wider civilian markets after wars ended. Urban populations in Victorian
Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...
demanded ever-increasing quantities of cheap, varied, quality food that they could keep at home without having to go shopping daily. In response, companies such as
Underwood Underwood may refer to: People *Underwood (surname), people with the surname Places United States * Underwood, Shelby County, Alabama * Underwood, Indiana * Underwood, Iowa * Underwood, Minnesota * Underwood, New York * Underwood, North Dakota * ...
,
Nestlé Nestlé S.A. (; ; ) is a Switzerland, Swiss multinational food and drink processing conglomerate corporation headquartered in Vevey, Vaud, Switzerland. It is the largest publicly held food company in the world, measured by revenue and other me ...
,
Heinz The H. J. Heinz Company is an American food processing company headquartered at One PPG Place in Pittsburgh, Pennsylvania. The company was founded by Henry J. Heinz in 1869. Heinz manufactures thousands of food products in plants on six conti ...
, and others provided quality canned food for sale to
working class The working class (or labouring class) comprises those engaged in manual-labour occupations or industrial work, who are remunerated via waged or salaried contracts. Working-class occupations (see also " Designation of workers by collar colou ...
city-dwellers. The late 19th century saw the range of canned food available to urban populations greatly increase, as canners competed with each other using novel foodstuffs, highly decorated printed labels, and lower prices.


World War I

Demand for canned food skyrocketed during
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, as military commanders sought vast quantities of cheap, high-
calorie The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of on ...
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...
to feed their millions of soldiers, which could be transported safely, survive
trench A trench is a type of excavation or in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole or pit). In geology, trenches result from eros ...
conditions, and not spoil in transport. Throughout the war, British soldiers generally subsisted on low-quality canned foodstuffs, such as the British "Bully Beef" (cheap
corned beef Corned beef, or salt beef in some of the Commonwealth of Nations, is Salt-cured meat, salt-cured brisket of beef. The term comes from the treatment of the meat with large-grained rock salt, also called "corns" of salt. Sometimes, sugar and sp ...
),
pork and beans Pork and beans is a culinary dish that uses pork and beans as its main ingredients. Numerous variations exist, usually with a more specific name, such as Fabada Asturiana, Olla podrida, or American canned pork and beans. American canned pork a ...
, canned sausages, and Maconochies Irish Stew, but by 1916, widespread dissatisfaction and increasing complaints about the poor quality canned food among soldiers resulted in militaries seeking better-quality food to improve morale, and complete meals-in-a-can began to appear. In 1917, the
French Army The French Army, officially known as the Land Army (french: Armée de Terre, ), is the land-based and largest component of the French Armed Forces. It is responsible to the Government of France, along with the other components of the Armed For ...
began issuing canned
French cuisine French cuisine () is the cooking traditions and practices from France. It has been influenced over the centuries by the many surrounding cultures of Spain, Italy, Switzerland, Germany and Belgium, in addition to the food traditions of the re ...
, such as
coq au vin ''Coq au vin'' (; , "rooster/cock with wine") is a French dish of chicken braised with wine, lardons, mushrooms, and optionally garlic. A red Burgundy wine is typically used, though many regions of France make variants using local wines, such ...
,
Beef Bourguignon Beef bourguignon () or bœuf bourguignon (; ), also called beef Burgundy, and ''bœuf à la Bourguignonne'',''Random House Dictionary'online at dictionary.com/ref> is a French cuisine, French beef stew braised in red wine, often red Burgundy wine ...
,
french onion soup French onion soup (French: ''soupe à l’oignon'' ) is a soup usually based on meat stock and onions, and often served gratinéed with croutons or a larger piece of bread covered with cheese floating on top. Ancient in origin, the dish underwe ...
and
Vichyssoise Vichyssoise ( , ), also known as potage Parmentier, velouté Parmentier, or crème Parmentier, is a thick soup made of boiled and puréed leeks, onions, potatoes, cream, and chicken stock. It is traditionally served cold, but it can be eaten hot. ...
, while the
Italian Army "The safeguard of the republic shall be the supreme law" , colors = , colors_labels = , march = ''Parata d'Eroi'' ("Heroes's parade") by Francesco Pellegrino, ''4 Maggio'' (May 4) ...
experimented with canned
ravioli Ravioli (; singular: ''raviolo'', ) are a type of pasta comprising a filling enveloped in thin pasta dough. Usually served in broth or with a sauce, they originated as a traditional food in Italian cuisine. Ravioli are commonly square, though o ...
,
spaghetti bolognese Bolognese sauce (, ; known in Italian as ''ragù alla bolognese'', , ''ragù bolognese'', or simply ''ragù'') is a meat-based sauce in Italian cuisine, typical of the city of Bologna. It is customarily used to dress ''tagliatelle al ragù'' and ...
,
Minestrone Minestrone (; ) is a thick soup of Italian origin made with vegetables, often with the addition of pasta or rice, sometimes both. Common ingredients include beans, onions, celery, carrots, leaf vegetables, stock, parmesan cheese and tomatoes ...
and
Pasta e fagioli ''Pasta e fagioli'' (), meaning "pasta and beans", is a traditional Italian pasta soup. It is often called pasta fasul or pasta fazool in the New York Italian dialect, derived from its Neapolitan name, ''pasta e fasule''. Preparation Recipes for ...
. Shortages of canned food in the
British Army The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurk ...
during 1917 led to the government issuing large quantities of
cigarette A cigarette is a narrow cylinder containing a combustible material, typically tobacco, that is rolled into thin paper for smoking. The cigarette is ignited at one end, causing it to smolder; the resulting smoke is orally inhaled via the opp ...
s and
amphetamine Amphetamine (contracted from alpha- methylphenethylamine) is a strong central nervous system (CNS) stimulant that is used in the treatment of attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. It is also commonly used ...
s to soldiers to suppress their appetites. After the war, companies that had supplied military canned food sought to improve the quality of their goods for civilian sale.


Methods

The original fragile and heavy glass containers presented challenges for transportation, and glass jars were largely replaced in commercial canneries with cylindrical
tin can A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans re ...
or wrought-iron canisters (later shortened to "cans") following the work of
Peter Durand Peter Durand (21 October 1766 – 23 July 1822) was an English merchant who is widely credited with receiving the first patent for the idea of preserving food using tin cans. The patent (No 3372) was granted on August 25, 1810, by King George III ...
(1810). Cans are cheaper and quicker to make, and much less fragile than glass jars.
Can opener A can opener (in North American English and Australian English) or tin opener (used in British English) is a mechanical device used to open tin cans (metal cans). Although canning, preservation of food using tin cans had been practiced since ...
s were not invented for another thirty years – at first, soldiers had to cut the cans open with
bayonet A bayonet (from French ) is a knife, dagger, sword, or spike-shaped weapon designed to fit on the end of the muzzle of a rifle, musket or similar firearm, allowing it to be used as a spear-like weapon.Brayley, Martin, ''Bayonets: An Illustr ...
s or smash them open with rocks. Today, tin-coated
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
is the material most commonly used. Laminate vacuum pouches are also used for canning, such as used in
MRE A Meal, Ready-to-Eat (MRE) is a self-contained, individual field ration in lightweight packaging purchased by the United States Department of Defense for its service members for use in combat or field conditions where other food is not avail ...
s and
Capri Sun Capri Sun (, , stylized as CAPRISUN in the United States and Capri-Sun internationally) is a German brand of juice concentrate drinks owned by Capri Sun Group Holding in Germany, which is a privately held company of Hans-Peter Wild. It was in ...
drinks. Glass jars have remained popular for some high-value products and in
home canning Home canning or bottling, also known colloquially as putting up or processing, is the process of preserving foods, in particular, fruits, vegetables, and meats, by packing them into glass jars and then heating the jars to create a vacuum seal and ...
.


Microbial control

To prevent the food from being spoiled before and during containment, a number of methods are used: pasteurisation, boiling (and other applications of high temperature over a period of time), refrigeration, freezing, drying, vacuum treatment, antimicrobial agents that are natural to the recipe of the foods being preserved, a sufficient dose of ionizing radiation, submersion in a strong saline solution, acid, base, osmotically extreme (for example very sugary) or other microbially-challenging environments. Other than sterilization, no method is perfectly dependable as a preservative. For example, the spores of the microorganism ''
Clostridium botulinum ''Clostridium botulinum'' is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum. The botulinum toxin can cause botulism, a severe flaccid paralytic disease in humans an ...
'' (which causes
botulism Botulism is a rare and potentially fatal illness caused by a toxin produced by the bacterium ''Clostridium botulinum''. The disease begins with weakness, blurred vision, feeling tired, and trouble speaking. This may then be followed by weaknes ...
) can be eliminated only at temperatures above the boiling point of water. From a public safety point of view, foods with low
acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
(a pH more than 4.6) need sterilization under high temperature (116–130 °C). To achieve temperatures above the boiling point requires the use of a pressure canner. Foods that must be pressure canned include most
vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...
s,
meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
,
seafood Seafood is any form of sea life regarded as food by humans, prominently including fish and shellfish. Shellfish include various species of molluscs (e.g. bivalve molluscs such as clams, oysters and mussels, and cephalopods such as octopus an ...
,
poultry Poultry () are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes (which includes chickens, quails, a ...
, and
dairy A dairy is a business enterprise established for the harvesting or processing (or both) of animal milk – mostly from cows or buffaloes, but also from goats, sheep, horses, or camels – for human consumption. A dairy is typically located on ...
products. The only foods that may be safely canned in an ordinary boiling water bath are highly
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
ic ones with a pH below 4.6, such as
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
s,
pickled Pickling is the process of preserving or extending the shelf life of food by either anaerobic fermentation in brine or immersion in vinegar. The pickling procedure typically affects the food's texture and flavor. The resulting food is called ...
vegetables, or other foods to which acidic additives have been added.


Sealing: double seams

Invented in 1888 by Max Ams, modern
double seam A double seam is a canning process for sealing a tin can by mechanically interlocking the can body and a can end (or lid). Originally, the can end was soldered or welded onto the can body after the can was filled. However, this introduced a var ...
s provide an airtight
seal Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...
to the
tin can A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans re ...
. This airtight nature is crucial to keeping micro-organisms out of the can and keeping its contents sealed inside. Thus, double seamed cans are also known as Sanitary Cans. Developed in 1900 in Europe, this sort of can was made of the traditional cylindrical body made with
tin plate Tinplate consists of sheets of steel coated with a thin layer of tin to impede rusting. Before the advent of cheap milled steel, the backing metal was wrought iron. While once more widely used, the primary use of tinplate now is the manufacture ...
. The two ends ( lids) were attached using what is now called a double seam. A can thus sealed is impervious to contamination by creating two tight continuous folds between the can's cylindrical body and the lids. This eliminated the need for
solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...
and allowed improvements in manufacturing speed, reducing cost. Double seaming uses rollers to shape the can, lid and the final double seam. To make a sanitary can and lid suitable for double seaming, manufacture begins with a sheet of coated tin plate. To create the can body, rectangles are cut and curled around a die, and welded together creating a cylinder with a side seam. Rollers are then used to flare out one or both ends of the cylinder to create a quarter circle flange around the circumference. Precision is required to ensure that the welded sides are perfectly aligned, as any misalignment will cause inconsistent flange shape, compromising its integrity. A circle is then cut from the sheet using a die cutter. The circle is shaped in a stamping press to create a downward countersink to fit snugly into the can body. The result can be compared to an upside down and very flat
top hat A top hat (also called a high hat, a cylinder hat, or, informally, a topper) is a tall, flat-crowned hat for men traditionally associated with formal wear in Western dress codes, meaning white tie, morning dress, or frock coat. Traditionally m ...
. The outer edge is then curled down and around about 140 degrees using rollers to create the end curl. The result is a steel tube with a flanged edge, and a countersunk steel disc with a curled edge. A
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...
compound is put inside the curl.


Seaming

The body and end are brought together in a seamer and held in place by the base plate and chuck, respectively. The base plate provides a sure footing for the can body during the seaming operation and the chuck fits snugly into the end (lid). The result is the countersink of the end sits inside the top of the can body just below the flange. The end curl protrudes slightly beyond the flange.


First operation

Once brought together in the seamer, the seaming head presses a first operation roller against the end curl. The end curl is pressed against the flange curling it in toward the body and under the flange. The flange is also bent downward, and the end and body are now loosely joined together. The first operation roller is then retracted. At this point five thicknesses of steel exist in the seam. From the outside in they are: *End *Body Hook *Cover Hook *Body *Countersink


Second operation

The seaming head then engages the second operation roller against the partly formed seam. The second operation presses all five steel components together tightly to form the final seal. The five layers in the final seam are then called; a) End, b) Body Hook, c) Cover Hook, d) Body, e) Countersink. All sanitary cans require a filling medium within the seam because otherwise the metal-to-metal contact will not maintain a hermetic seal. In most cases, a rubberized compound is placed inside the end curl radius, forming the critical seal between the end and the body. Probably the most important innovation since the introduction of double seams is the welded side seam. Prior to the welded side seam, the can body was folded and/or soldered together, leaving a relatively thick side seam. The thick side seam required that the side seam end juncture at the end curl to have more metal to curl around before closing in behind the Body Hook or flange, with a greater opportunity for error.


Seamer setup and quality assurance

Many different parts during the seaming process are critical in ensuring that a can is airtight and vacuum sealed. The dangers of a can that is not hermetically sealed are contamination by foreign objects (bacteria or fungicide sprays), or that the can could leak or spoil. One important part is the seamer setup. This process is usually performed by an experienced technician. among the parts that need setup are seamer rolls and chucks which have to be set in their exact position (using a feeler gauge or a
clearance gauge Clearance can refer to: Engineering * Engineering tolerance, a physical distance or space between two components * Ride height (vehicle clearance) * Hydraulic clearance * Clearance in civil engineering ** Ground clearance, the amount of space b ...
). The lifter pressure and position, roll and chuck designs, tooling wear, and bearing wear all contribute to a good
double seam A double seam is a canning process for sealing a tin can by mechanically interlocking the can body and a can end (or lid). Originally, the can end was soldered or welded onto the can body after the can was filled. However, this introduced a var ...
. Incorrect setups can be non-intuitive. For example, due to the springback effect, a seam can appear loose, when in reality it was closed too tight and has opened up like a spring. For this reason, experienced operators and good seamer setup are critical to ensure that double seams are properly closed. Quality control usually involves taking full cans from the line – one per seamer head, at least once or twice per shift, and performing a teardown operation (
wrinkle A wrinkle, also known as a rhytid, is a fold, ridge or crease in an otherwise smooth surface, such as on skin or fabric. Skin wrinkles typically appear as a result of ageing processes such as glycation, habitual sleeping positions, loss of bo ...
/ tightness), mechanical tests (external thickness, seamer length/height and countersink) as well as cutting the seam open with a twin blade saw and measuring with a double seam inspection system. The combination of these measurements will determine the seam's quality. Use of a
statistical process control Statistical process control (SPC) or statistical quality control (SQC) is the application of statistical methods to monitor and control the quality of a production process. This helps to ensure that the process operates efficiently, producing m ...
(SPC) software in conjunction with a manual double-seam monitor, computerized double seam scanner, or even a fully automatic double seam inspection system makes the laborious process of double seam inspection faster and much more accurate. Statistically tracking the performance of each head or seaming station of the
can seamer A can seamer is a machine used to seal the lid to the can body. The lid or "end" is usually tinplated steel (food) or aluminum (drinks) while the body can be of metal (such as cans for beverages and soups), paperboard (whisky cans) or plastic. Th ...
allows for better prediction of can seamer issues, and may be used to plan maintenance when convenient, rather than to simply react after bad or unsafe cans have been produced.


Nutritional value

Canning is a way of processing food to extend its
shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
. The idea is to make food available and edible long after the processing time. A 1997 study found that canned fruits and vegetables are as rich with
dietary fiber Dietary fiber (in British English fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition, and can be grouped generally by the ...
and
vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, essential micronutrient that an organism needs in small quantities for the proper functioning of its ...
s as the same corresponding fresh or frozen foods, and in some cases the canned products are richer than their fresh or frozen counterparts. The heating process during canning appears to make dietary fiber more soluble, and therefore more readily fermented in the colon into gases and physiologically active byproducts. Canned tomatoes have a higher available
lycopene Lycopene is an organic compound classified as a tetraterpene and a carotene. Lycopene (from the neo-Latin ''Lycopersicum'', the tomato species) is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and vegetables. Occu ...
content. Consequently, canned meat and vegetables are often among the list of food items that are stocked during emergencies.


Potential hazards

In the beginning of the 19th century the process of canning foods was mainly done by small canneries. These canneries were full of overlooked sanitation problems, such as poor hygiene and unsanitary work environments. Since the refrigerator did not exist and industrial canning standards were not set in place it was very common for contaminated cans to slip onto the grocery store shelves. According to ''The Fruits of Empire: Art, Food and the Politics of Race in the Age of American Expansion'' by Shana Klein, "Workers also suffered injuries, specifically bruised knuckles and open sores, from trimming and packaging pineapples. Gloves were one preventative measure to protect a canner's hands from the acidity of the pineapple, but gloves did not always help."


Migration of can components

In canning toxicology, ''migration'' is the movement of substances from the can itself into the contents. Potential toxic substances that can migrate are lead, causing
lead poisoning Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, inferti ...
, or
bisphenol A Bisphenol A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on an industrial s ...
(BPA), a potential
endocrine disruptor Endocrine disruptors, sometimes also referred to as hormonally active agents, endocrine disrupting chemicals, or endocrine disrupting compounds are chemicals that can interfere with endocrine (or hormonal) systems. These disruptions can cause c ...
that is an ingredient in the epoxy commonly used to coat the inner surface of cans. Some cans are manufactured with a BPA-free enamel lining produced from plant oils and resins. In February 2018, the Can Manufacturers Institute, a trade association in the United States, surveyed the industry and reported that at least 90% of food cans no longer contained BPA.


Salt content

Salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
(sodium chloride), dissolved in water, is used in the canning process. As a result, canned food can be a major source of dietary salt. Too much salt increases the risk of health problems, including
high blood pressure Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
. Therefore, health authorities have recommended limitations of dietary sodium. Many canned products are available in low-salt and no-salt alternatives. Rinsing thoroughly after opening may reduce the amount of salt in canned vegetables, since much of the salt content is thought to be in the liquid, rather than the food itself.


Botulism

Foodborne
botulism Botulism is a rare and potentially fatal illness caused by a toxin produced by the bacterium ''Clostridium botulinum''. The disease begins with weakness, blurred vision, feeling tired, and trouble speaking. This may then be followed by weaknes ...
results from contaminated foodstuffs in which ''
C. botulinum ''Clostridium botulinum'' is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum. The botulinum toxin can cause botulism, a severe flaccid paralytic disease in humans a ...
'' spores have been allowed to germinate and produce botulism toxin,Botox and Botulism? Beauty and the Beast?
From Ingrid Koo, PhD, for About.com. Updated: 16 December 2008
and this typically occurs in canned non-acidic food substances that have not received a strong enough thermal heat treatment. ''C. botulinum'' prefers low oxygen environments and is a poor competitor to other bacteria, but its spores are resistant to thermal treatments. When a canned food is sterilized insufficiently, most other bacteria besides the ''C. botulinum'' spores are killed, and the spores can germinate and produce botulism toxin. Botulism is a rare but serious
paralytic Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 50 ...
illness, leading to paralysis that typically starts with the muscles of the face and then spreads towards the limbs. The botulinum toxin is extremely dangerous because it cannot be detected by sight or smell, and ingestion of even a small amount of the toxin can be deadly. In severe forms, it leads to paralysis of the breathing muscles and causes
respiratory failure Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise ...
. In view of this life-threatening complication, all suspected cases of botulism are treated as
medical emergencies A medical emergency is an acute injury or illness that poses an immediate risk to a person's life or long-term health, sometimes referred to as a situation risking "life or limb". These emergencies may require assistance from another, qualified p ...
, and
public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
officials are usually involved to prevent further cases from the same source.


Canning and economic recession

Canned goods and canning supplies sell particularly well in times of recession due to the tendency of financially stressed individuals to engage in cocooning, a term used by retail analysts to describe the phenomenon in which people choose to stay at home instead of adding expenditures to their budget by dining out and socializing outside the home.. Also, some people may become
prepper Survivalism is a social movement of individuals or groups (called survivalists or preppers) who proactively prepare for emergencies, such as natural disasters, as well as other disasters causing disruption to social order (that is, civil disord ...
s and proceed to stockpile canned food. A
doomer Doomer and, by extension, doomerism are terms which arose primarily on the Internet to describe people who are extremely pessimistic or fatalist about global problems such as overpopulation, peak oil, climate change, and pollution. Some doomers ...
would also be interested in stockpiling canned food upon learning about a recession. In February 2009 during a recession, the United States saw an 11.5% rise in sales of canning-related items. Some communities in the US have county canning centers which are available for teaching canning, or shared community kitchens which can be rented for canning one's own foods.


Occupation


In popular culture

Artist
Andy Warhol Andy Warhol (; born Andrew Warhola Jr.; August 6, 1928 – February 22, 1987) was an American visual artist, film director, and producer who was a leading figure in the visual art movement known as pop art. His works explore the relationsh ...
is famous for depicting Campbell's Soup cans, notably ''
Campbell's Soup Cans ''Campbell's Soup Cans'' (sometimes referred to as ''32 Campbell's Soup Cans'') is a Visual arts, work of art produced between November 1961 and March or April 1962 by American artist Andy Warhol. It consists of thirty-two canvases, each mea ...
'' (1962). There was a 1956 US documentary ''The Miracle of the Can'' that mentions the Pea Tenderomiter for the canning trade.


See also


References


Further reading

* FDA 21CFR113.
Thermally processed low acid foods packaged in hermetically sealed containers
Revision Apr. 2006 * Potter, N. N. and Hotchkiss, J. H. ''Food Science'' (5th ed). Springer, 1999 * Fellows, P. J. ''Food Processing Technology: Principles and Practice'' (2nd Edition). Woodhead Pub. 1999 *


External links



* Boston Public Library, USA
Canned food advertisements
various dates
1956 American Can Co Video: "Miracle of the Can"
In addition to historical propaganda, contains an in-depth review of the industrial canning process. * List of canned food manufacturer
Canned food directory
{{Authority control 19th-century inventions Canneries Food storage containers Food packaging Industrial processes French inventions