What is Canning?
Canning is a method of preservation of food in which the food is processed and hermetically sealed in containers (of metal, glass, thermo stable plastic, or a multi-layered flexible pouch) through agency of heat.
Canning provides a shelf life typically ranging from one to five years, although under specific circumstances it can be much longer.
Heating is the principle factor to destroy the microorganisms and the permanent sealing is to prevent re-infection.
Why is Canning done?
The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their quality for several reasons.
Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised, insect damaged, and diseased food. Oxygen and enzymes are present throughout fresh food tissues. Proper canning practices minimize the effects of these microorganisms.
However, the main objective of canning is to preserve the food by the application of heat so that it can be safely eaten at a later time. Safety of the consumer is the primary concern when food is canned.
During the first years of the Napoleonic wars, 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. In 1809, Nicolas Appert , 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 which was referred to as APPERTIZATION and now known as CANNING.
Foods that are canned:
(a) Low acid foods: Meat, fish, poultry, dairy fall into a pH range of 5.0 to 6.8. This large group is commonly referred to as the low acid group.
(b) Acid foods: With pH values between 4.5 and 3.7. Fruits such as pear, oranges, apricots and tomatoes fall in this class.
(c) High acid foods: Such as pickled products and fermented foods. The pH values range from 3.7 down to 2.3, also Jams and Jellies are in this classification.