Canning is one of the preservation methods in which processed food is sealed in an airtight container to destroy microorganisms that can cause food spoilage. Canned food usually remains edible for one to five years, though certain conditions may allow for significantly extended storage times.
In this method, heating and permanent sealing are the fundamental principles to kill microorganisms and prevent re-infection in preserved food products.
This food preserving method was originated in the 19th century with Napoleon’s need to preserve meat for his armies. It evolved from glass jars to tin cans, revolutionizing food preservation. With mass production, canning became popular worldwide, helping food last longer.
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Types of Canning
There are two ways of canning based on food types. These include;
Boiling Water Bath Method
- It is an effective method for preserving highly acidic foods (pH of 4.6 or less) such as fruits, tomatoes, jams, jellies, etc.
- In this method, the jars are filled with prepared food, sealed with lids, and then immersed in boiling water for a specific time to destroy bacteria and create a vacuum seal.
- Foods like tomatoes and figs whose pH is less than 4.6 can be preserved by adding acid during boiling.
Pressure Canning Method
- It helps preserve low-acid foods such as vegetables, meats, seafood, and soups.
- Such types of food have a pH level above 4.6, which means they are not acidic, which is enough to inhibit the growth of harmful bacteria. Therefore, this type of method requires high temperatures to inhibit the growth of such harmful bacteria.
- The process of pressure canning involves using a specialized pressure canner, which is a large pot with a locking lid and a venting system. Additionally, the pressure canner has a gauze to measure pressure, allowing precise control.
Procedure of Canning
The canning techniques vary based on the food used. However, some of the general procedures that are applied during canning are as follows;
- For canning, fruits, and vegetables should be fresh.
- The fruits should be ripe but firm and evenly matured.
- It should be free from blemishes, insect damage, soil, dirt, and malfunction.
Sorting and Grading
- After the preliminary sorting, the fruits and vegetables are graded based on size and color.
- The grading is done by hand or with the grading machine (e.g., screen graders, roller graders, rope or cable graders).
- The graded fruits and vegetables are washed with water in different ways, such as; agitation, soaking, or spraying with water.
- Vegetables may be preferably soaked in a dilute solution of potassium permanganate to disinfect them.
Peeling, Coring, Pitting
- Peeling is done in various ways (such as; by hand or knife, machine, heat treatment, or boiling fruits or vegetables in a caustic soda or lyse solution for 30 seconds to 2 minutes).
- Similarly, the coring and pitting of fruits and vegetables are done by hand or machine.
- Treatment of fruits and vegetables with steam or boiling water for a specific period before cooling is termed blanching.
- The primary purpose of blanching is; to loosen the skin of fruits and vegetables, kill microorganisms, inactivate the enzymes, and improve the flavor by reducing sourness.
Filling of Cans
- Hot food is put into heated cans, which are also kept hot to allow the food to expand and remove any trapped air or gas.
- Before filling the fruits or vegetables, a small amount of syrup (for fruits) or brine (for vegetables) is poured into the can to provide medium to the contents.
- Filling cans is done either by hand or via machines. Additionally, cans are partially filled, leaving space for the food to expand during heating.
- After filling, bringing or syrup is added.
- Exhausting is the method of removing air from the cans before they are closed.
- It reduces the pressure tension on can seams and internal corrosion and helps maintain the quality of products.
- Cans are immediately sealed after removing air with the help of double seam can sealer.
- While sealing, make sure the temperature is not below 74℃.
- It consists of heat treatment sufficient to eliminate spoilage microorganisms’ growth.
- All foods are processed at 100 ℃ and vegetables at 116-120℃.
- The total time required to sterilize the can depends on various factors such as; size, processing temperature, rate of heat penetration at the center of the can, pH of food, and the type and many microorganisms present.
- After thermal processing, cans are immediately cooled at 39℃ to stop the cooking process to prevent overheating/ burning.
- Usually, cans are cooled by dipping them in cold water.
Labeling and Storage
- After scanning, the cans are labeled, packaged, and stored in a clean and dry place.
- Storage temperature should be maintained based on preserved food types.
Applications of Canning
The applications of canning food preservation methods are as follows;
- It is used to preserve varieties of foods such as; fruits and vegetables.
- It provides convenience and accessibility by allowing ready-to-eat or easy-to-prepare meals throughout the year.
- Canned foods are crucial for emergency preparedness, providing a reliable food supply during emergencies.
- It supports local agriculture by preserving locally grown produce.
- Canning reduces food waste by preserving surplus food.
Advantages of Canning
Some of the advantages of the canning food preservation method are as follows;
- It provides a long shelf life of preserved food (i.e., 1 to 5 years; in some cases, it can increase to more than 20 years).
- It provides higher stability of preserved food than traditional packaging methods.
- Materials used (i.e., tin or glass jars) are reusable.
- The pull-off lid makes food packed by the canning method easy to open.
- Foods preserved by the canning method are of high quality as few or fewer preservatives are added.
- Foods preserved by the canning method are easy to prepare and store.
- Canned food does not require a refrigerator for storage.
- It does not require cold chaining during transportation.
Disadvantages of Canning
Despite having benefits, canning also has some disadvantages, which are as follows;
- The glass jar might break.
- Breaking of seals can cause spoilage.
- If you don’t process the food correctly or keep things unclean, it can lead to a harmful bacteria called Clostridium botulinum contaminating the food. It’s essential always to follow the instructions that come with your canner to stay safe.
- The can food does not taste the same as fresh food.
- Can food may have fewer vitamins and minerals than fresh food. Canned fruits and vegetables have about 65% fewer vitamins and minerals than freshly picked ripe fruits and vegetables.
- Canning requires much time.
Some of the precautions that are needed to consider while canning are as follows;
- Before storing, the sealing of canned food should be checked appropriately.
- Always store canned foods in a clean, dry, and dark place.
- Frazier W.C, Westhoff D.C, and Vanitha N.M. (2014). Food Microbiology. New Delhi: McGraw Hill Education Private Limited.