Canning
<p ><b>Canning</b> is a method of <a href="http://en.wikipedia.org/wiki/Food_preservation" title="Food preservation" >preserving food</a> in which the food contents are processed and sealed in an airtight container. Canning provides a typical shelf life ranging from one to five years, although under specific circumstances a freeze-dried canned product, such as canned, dried lentils, can last as long as 30 years in an edible state. In 1795 the French military offered a cash price of 12,000 francs for a new method to preserve food. <a href="http://en.wikipedia.org/wiki/Nicolas_Appert" title="Nicolas Appert" >Nicolas Appert</a> suggested canning and the process was first proven in 1806 in test with the French navy and the prize awarded in 1809 or 1810.</p>
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The <a href="http://en.wikipedia.org/wiki/Packaging" title="Packaging" class="mw-redirect" >packaging</a> prevents <a href="http://en.wikipedia.org/wiki/Microorganism" title="Microorganism" >microorganisms</a> from entering and proliferating inside.</p>
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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.</p>
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Other than <a href="http://en.wikipedia.org/wiki/Sterilization_(microbiology)" title="Sterilization (microbiology)" >sterilization</a>, no method is perfectly dependable as a preservative. For example, the microorganism <i><a href="http://en.wikipedia.org/wiki/Clostridium_botulinum" title="Clostridium botulinum" >Clostridium botulinum</a></i> (which causes <a href="http://en.wikipedia.org/wiki/Botulism" title="Botulism" >botulism</a>), can only be eliminated at temperatures above the boiling point.</p>
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From a public safety point of view, foods with low <a href="http://en.wikipedia.org/wiki/Acidity" title="Acidity" class="mw-redirect" >acidity</a> (a <a href="http://en.wikipedia.org/wiki/PH" title="PH" >pH</a> more than 4.6) need sterilization under high temperature (116-130 °C). To achieve temperatures above the boiling point requires the use of a <a href="http://en.wikipedia.org/wiki/Pressure_cooking" title="Pressure cooking" >pressure canner</a>. </p>
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Foods that must be pressure canned include most <a href="http://en.wikipedia.org/wiki/Vegetable" title="Vegetable" >vegetables</a>, <a href="http://en.wikipedia.org/wiki/Meat" title="Meat" >meat</a>, <a href="http://en.wikipedia.org/wiki/Seafood" title="Seafood" >seafood</a>, <a href="http://en.wikipedia.org/wiki/Poultry" title="Poultry" >poultry</a>, and <a href="http://en.wikipedia.org/wiki/Dairy" title="Dairy" >dairy</a> products. </p>
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The only foods that may be safely canned in an ordinary boiling water bath are highly <a href="http://en.wikipedia.org/wiki/Acid" title="Acid" >acidic</a> ones with a pH below 4.6,<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Canning#cite_note-0" >[1]</a></sup> such as <a href="http://en.wikipedia.org/wiki/Fruit" title="Fruit" >fruits</a>, <a href="http://en.wikipedia.org/wiki/Pickling" title="Pickling" >pickled</a> vegetables, or other foods to which acidic additives have been added.</p>