Canned fish are fish which have been processed, sealed in an airtight container such as a sealed tin can, and subjected to heat. Canning is a method of preserving food, and provides a typical shelf life ranging from one to five years.
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 leading to a loss of fish quality. Spoilage bacteria are the specific bacteria that produce the unpleasant odours and flavours associated with spoiled fish.
Sardines are canned in many different ways. At the cannery, the fish are washed, their heads are removed, and the fish are cooked, either by deep-frying or by steam-cooking, after which they are dried. They are then packed in either olive, sunflower or soybean oil, water, or in a tomato, chilli or mustard sauce.
Canned sardines in supermarkets may actually be sprat (such as the “brisling sardine”) or round herrings. Fish sizes vary by species. Good quality sardines should have the head and gills removed before packing. They may also be eviscerated before packing (typically the larger varieties). If not, they should be purged of undigested or partially digested food or feces by holding the live fish in a tank long enough for them to empty their digestive systems.
Sardines are typically tightly packed in a small can which is scored for easy opening, either with a pull tab (similar to how a beverage can is opened), or a key, attached to the underside of the can. Thus, it has the virtues of being an easily portable, non-perishable, self-contained food.