Canning is a method of preserving food, and provides a typical shelf life ranging from one to five years. A means of obtaining long-term microbiological stability for non-dried foods without the use of refrigeration, by prolonged heating in hermetically sealed containers, such as cans to render the contents of the container sterile.
Fish have a low acidity at levels where microbes can flourish. 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 a method of pressurized cooking which is provided by the containment within the can. After sterilization, the containing can prevents microorganisms from entering and proliferating inside. 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.
Such preservation techniques are needed to prevent fish spoilage and lengthen shelf life. They are designed to inhibit the activity of spoilage bacteria and the metabolic changes that result in the loss of fish quality. Spoilage bacteria are the specific bacteria that produce the unpleasant odours and flavours associated with spoiled fish.