Food when processed, sealed and preserved in airtight containers is called canned food or processed food. Canning improves the shelf life of the food content ranging from one to five years.
Canning is a safe method for preserving food. It involves placing foods in jars and heating them to a temperature that destroys microorganisms that cause food to spoil. Air is driven out during heating the jar. As the jar cools a vacuum is created. This vacuum seal prevents air from getting back into the product bringing with it contaminating microorganisms.
The first canned food was preserved in glass containers. Being fragile, it posed a challenge in transportation. This was replaced by cylindrical tin canisters or wrought iron canisters (later shortened to cans). Cans proved to be cheaper and less fragile. Tin-coated steel is most commonly used now a days.
Canning is a way of processing food to extend its shelf life. This makes food edible even after several years of processing. A 1997 study found that canned fruits and vegetables are as rich with dietary fiber and vitamins as the same corresponding fresh or frozen foods, and in some cases the canned products are richer than their fresh or frozen counterparts.The heating process during canning appears to make dietary fiber more soluble, and therefore more readily fermented in the colon into gases and physiologically active byproducts. Canned tomatoes have a higher available lycopene content.
Safe Canning Methods
Canning can be done in two ways:
- Boiling water bath method - Jar containing food is heated in boiling water. This method is used for tomatoes, fruits, jams, jellies, pickles and other preserves.
- Pressure canning - Jars containing food are dipped in 2-3 inches of water in a pressure cooker and heated. This kills bacteria. This method is used for vegetable, meat, seafood and poultry.
Handling of Canned Food
Usage and storage
- It is important that canned foods are stored well. They must be stored in such a manner that they are not damaged physically. Any tear can lead to microbial contamination. Discard any can or pack that is puffed or leaking.
- Before they are opened, most canned can be stored at room temperature. Some products should be consumed immediately after opening. Some must be refrigerated after opening. The duration for safe consumption after opening the pack is clearly mentioned on the pack.
- Refer to the instructions given on the food label. There are clear instructions about handling of the food, such as heating methods, duration for which it is to be heated, and any other precautions that one must take while handling the product. The label clearly declares that the product must be consumed within certain days after they are opened.
- If you stock canned foods, consume the product that is about to expire earlier.
- Before consumption, carefully check the product. Discard a product that has an off odour, unusual appearance, or aftertaste.
Things to keep in mind while purchasing canned foods
Be very careful while selecting canned foods. These products are shelf-stable as they are carefully packed and sealed. Never purchase a leaking or puffed can or a torn Tetra-Pak. A puffed can indicates possible contamination and consumption of that product can lead to food poisoning.
Check the expiry dates. A product that has expired is unfit for human consumption.