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'Canning' is a method of preserving food by first sealing it in air-tight jars, cans or pouches, and then heating it to a temperature that destroys contaminating microorganisms that can either be of health or spoilage concern. Because of the danger posed by several spore-former thermo resistant microorganisms, such as ''Clostridium botulinum'' (the causative agent of botulism). Spores of C.Botulinum (in a concentration of 10⁴ /ml) can resist boiling at 100 C (212 F) for more than 300 minutes, however as temperature increases the times decrease exponentially, so at 121 C (250 F) for the same concentration just 2.8 minutes are required.
From a public safety point of view, foods with low acidity, i.e. pH > 4.3 need sterilization by canning under conditions of both high temperature (116-130 C) and pressure. 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[1], such as fruits, pickled vegetables, or other foods to which acid has been added.

Contents

History

Double Seams

Seaming

1st Operation

2nd Operation

See also

Incidents and accidents related to tinned foods

Famous canned foods

References

External links

History

During the early Revolutionary Wars, the notable French newspaper ''Le 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. The massive armies of the period required regular supplies of quality food, and so preservation became a necessity. In 1809, the French confectioner Nicolas François Appert observed that food cooked inside a jar did not spoil unless the seals leak, thus developed a method of sealing food inside glass jars. The reason why food did not spoil was unknown at the time, since it would take another 50 years before Louis Pasteur would confirm the existance of microbes. However, glass containers presented many challenges for transportation.
Glass jars were replaced with cylindrical tin or wrought-iron canisters (later shortened to "cans") following the work of Peter Durant (1810), which were both cheaper and quicker to make and much more resilient than fragile glass jars. Tin-openers were not to be invented for another thirty years — at first, soldiers had to cut the cans open with bayonets or smash them open with rocks. 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. Unfortunately for Appert, the factory which he had built with his prize money was burned down in 1814 by Allied soldiers invading France. Following the end of the Napoleonic Wars, the canning process was gradually put into practice in other European countries and in the United States. 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. In 1824 meats and stews produced by the Appert method were carried by