To prevent or retard spoilage, food must be preserved. Some of the more common food preservation processes are: drying, concentration, salting, fermentation, chilling, freezing, sugar preserving, chemical, irradiation, and heating in close containers (glass, metal or flexible). Some of these methods have been used for centuries, including food canning (sterilizing in airtight containers with exclusion of air) which is still used extensively for a large range of products. The most popular container for sterilized food is the tin can. South African consumes about 1 billion cans of food each year for which 80 000 tons of tin-plate are used.
History Of Canning
Concerned by the death of his soldiers from malnutrition, Napoleon appealed for a new way to preserve food other than with spices and salt. In response, Nicholas Appert, chef and confectioner, invented canning in 1809 and he was richly rewarded by Napoleon. Whereas Appert preserved his food by heating sealed bottles in boiling water, an English merchant, Peter Durand, adopted his method and preserved food in canisters, hence the word “can”. Since the original invention a lot of research has been done on heat sterilization, including other heating sources, resulting in optimum canning conditions to provide safe, tasty and nutritious food.
The Canning Process
The preparation prior to cooking will depend on the food product but fruits and vegetables are harvested (picked) sorted, cooked, and sealed in a can. The product in the hermetically sealed can is then sterilized by means of heat. Some cans are coated on the inside with a harmless protective lacquer, because meat and some fruits tend to change colour if brought into direct contact with tin-plate.
In the early days of canning sealed cans were sterilized by immersion in boiling water. Research has shown that heating at higher temperatures for shorter periods will produce the best quality foods. Today, heating in retorts at temperatures above 100ºC is standard practice in the canning industry.
Consumers are generally concerned that the canning process will have a detrimental effect on the nutritional value of especially fruit and vegetables. A study by the University of Illinois, USA, of 14 different fresh, canned and frozen fruits and vegetables showed that in most cases, canned fruits and vegetables are nutritionally equal to their fresh counterparts. Similar results were found in a study done by the Australian Government Analytical Laboratory. Even Vitamin C was not lost in canning to the extent expected by many people.
Therefore, if a fresh fruit or vegetable is an excellent source of a nutrient, it still is after it is canned. The reason for these results is that fruit and vegetables are canned within 24 hours after harvesting and so after canning nutritional value is retained. Fresh produce, on the other hand, could reach the consumer many days after harvesting.
Canned foods are convenient because they are already cooked and can be consumed hot or cold. An Australian household survey showed that 85% of households had bought canned food in the previous week. Canned foods have a long shellfire – anything up to 3 years depending on the product.
When using canned foods a few rules have to be followed. Once a can is opened the contents are just as prone to spoilage as fresh or cooked food because of the exposure to micro-organisms in the atmosphere. Once a can has been opened it is advisable to reclose the can with a plastic lid or clingwrap or transfer the food to a container with a lid and store in a refrigerator. Prevent cross contamination with other foods in the refrigerator. Acidic products, especially fruit and tomatoes should not be left in the can after opening. When heating food in a can (in boiling water) the top of the can has to be punctured. Reheating can also be done by emptying the food into a saucepan. To microwave, empty the can into a microwaveable container. Use the liquid in canned foods if possible, because it contains some of the nutrients and flavour. Bulging or leaking cans should be discarded. However, minor label stains, slight rust or small dents do not affect the contents of a can. Cans should be stored in a cool dry place. It is also good practice to date-mark cans on purchase and use within 12 months.
Canned foods are controlled by strict legislation, and quality standards in South Africa are amongst the toughest in the world. The South African Bureau of Standard (SABS) has compiled standard and compulsory specifications for locally and imported canned meat products and canned fish products, marine mollusks and crustaceans. These pertain for both products. The Department of Agriculture has compulsory standards for certain fruits and vegetables, including those for export. Certain products are graded; it pertains to appearance and not inherent quality. Undergrade is just as nutritious and safe as other grades.
F.A.C.S. Scientific Director. 2009. (Update 2017 imminent)