Food
Canning
Canning is a method of preserving
food 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.
Nicolas Appert suggested canning and the process
was first proven in 1806 in test with the French
navy and the prize awarded in 1809 or 1810. The
packaging prevents microorganisms from entering
and proliferating inside.
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 microorganism
Clostridium botulinum (which causes botulism), can
only be eliminated at temperatures above the boiling
point.
From a public safety point of view, foods with low
acidity (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 vegetables, meat, seafood, poultry,
and dairy products. The only foods that may be safely
canned in an ordinary boiling water bath are highly
acidic ones with a pH below 4.6, such as fruits,
pickled vegetables, or other foods to which acidic
additives have been added.
(Source: Wikipedia.org)
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