A food preservation process relying on the sterilization of foods by heating in a container sealed before or immediately after the heat treatment. The idea was first applied in 1810 by Nicolas Appert (c.17501841) to foods sealed in bottles and heated, but since 1839 in cans made of tinned thin steel sheet. Aluminium or plastic sometimes now replaces steel. Internal coatings are chosen to resist the chemical properties of different contents. The processes are now highly automated, and food growing is usually closely associated with a canning plant.
Canning is a method of preserving food by first heating it to a temperature that destroys contaminating microorganisms, and then sealing it in air-tight jars, cans or pouches. Because of the danger posed by Clostridium botulinum (the causative agent of botulism) and other pathogens, the only safe method of canning most foods is under conditions of both high heat and pressure, normally at temperatures of 240-250°F (116-121°C). Foods that must be pressure canned include most vegetables, meats, seafood, poultry, and dairy products. The only foods that may be safely canned in a boiling water bath (without high pressure) are highly acidic foods with a pH below 4.6, such as fruits, pickled vegetables, or other foods to which acid has been added.
History
Bottling
During the early Revolutionary Wars, the notable French newspaper Monde, prompted by the government, offered a hefty cash award of 12,000 Francs to any inventor who could come up with a cheap and effective method of preserving large amounts of food. In 1809, the French confectioner Nicolas François Appert developed a method of vacuum-sealing food inside glass jars. The French Army began experimenting with issuing tinned foods to its soldiers, but the slow process of tinning foods and the even slower development and transport stages prevented the army from shipping large amounts around the French Empire, and the war ended before the process could be perfected. Based on Appert's methods of food preservation, Peter Durand patented a process in the United Kingdom in 1810, developing a process of packaging food in sealed airtight wrought-iron cans. Initially, the canning process was slow and labour-intensive, as each can had to be hand-made and took up to six hours to cook properly, making tinned food too expensive for ordinary people to buy. Throughout the mid-nineteenth century, tinned food became a status symbol amongst middle-class households in Europe, becoming something of a frivolous novelty.
Increasing mechanisation of the canning process, coupled with a huge increase in urban populations across Europe, resulted in a rising demand for tinned food. Canned food also began to spread beyond Europe - Thomas Kensett established the first American canning factory in New York City in 1812, using improved tin-plated wrought-iron cans for preserving oysters, meats, fruits and vegetables. Demand for tinned food greatly increased during wars. Large-scale wars in the nineteenth century, such as the Crimean War, American Civil War, and Franco-Prussian War introduced increasing numbers of working-class men to tinned food, and allowed canning companies to expand their businesses to meet military demands for non-perishable food, allowing companies to manufacture in bulk and sell to wider civilian markets after wars ended. In response, companies such as Nestlé, Heinz, and others emerged to provide shops with good-quality tinned food for sale to ordinary working class city-dwellers. The late nineteenth century saw the range of tinned food available to urban populations greatly increase, as rival canning companies competed with each other using novel foodstuffs, highly decorated printed labels, and lower prices.
Demand for tinned food skyrocketed during the First World War, as military commanders sought vast quantities of cheap, high-calorie food to feed their millions of soldiers; Throughout the war soldiers generally subsisted on very low-quality tinned foodstuffs, such as the British "Bully Beef" (cheap corned beef) and Pork and Beans produced by the MacConnaughy Corporation, but by 1916 widespread boredom with cheap tinned food amongst soldiers resulted in militaries purchasing better-quality food, in order to improve low morale, and the first complete meals in a tin began to appear. Shortages of tinned food in the British Army in 1917 led to the government issuing cigarettes and even amphetamines to soldiers to suppress their appetites. After the war, companies that had supplied tinned food to national militaries improved the quality of their goods for sale on the civilian market.
Double Seams
Modern Double seams provide a hermetic seal to the can. The can was made of the traditional cylindrical body however the two ends were attached using what is now called a double seam. The can is sealed impervious to the outside world by creating two tight continuous folds between the can’s cylindrical body and the lid at each end.
Double seams make extensive use of rollers in shaping the can, lid and the final double seam. To create the can Body rectangles are cut and curled around a die and welded together leaving a Side Seam.
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 in to the End (lid).
1st Operation
Once brought together in the Seamer the Seaming Head presses a special 1st Operation roller against the End Curl. a) End, b) Flange, c) End Curl, d) Body, e) Countersink.
2nd Operation
The Seaming Head now engages the 2nd Operation roller against the partly formed seam.
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 meant that at the Side Seam End juncture the End Curl had more metal to curl around before closing in behind the Body Hook or Flange leaving a greater opportunity for error.
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