The process of sealing processed foods hermetically in containers after sterilizing them by heat for long-term usage is known as canning. Canning is one of the most popular food preservation techniques used today. Canning of fruits and vegetables and other highly perishable food items help reduce food waste.

Advantages of Canning

  1. Canning is the best food preservation technique to utilize all seasonal food items that are abundant in supply during seasons
  2. Fruits and vegetables are mostly seasonal and are highly perishable
  3. Wastage in food and vegetable industry is very high due to lack of proper infrastructure; in such cases preserving them for long-term usage is the best solution to avoid huge amount of food losses
  4. Fruits and vegetables may be canned during the seasons when they are in plenty of supply and these canned products can be sold during the off-season

Canning for Food Preservation: Food spoilage is caused by increased microbial activity. Canning means heating and/or cooling of foods so that microbes present in them tend to be inactive thus reduce the food spoilage due to microbial activity. Microbes that cause food spoilage include bacteria, fungi, molds etc. Canning process helps eliminate these microbes up to a great extent.

Disadvantages of Canning

  1. Canning requires hot water treatment which may reduce presence of water-soluble nutrients in the canned products
  2. In other words, canned products may not be as nutritious as fresh products
  3. Canning process affects, mostly reduces original flavour, aroma and taste of the fresh products
  4. Canning requires brining or syruping, thus increasing salt or sugar presence in the canned products which may not be desirable from a nutritional point of view

Selection of Fruits and Vegetables

Generally, all fruits and vegetables must be fresh, ripe, firm and uniformly mature; exceptions are there such as tomatoes which should be ripe and tender. They should be clean, free from foreign matter and dirt and devoid of any deformities and pest-disease infestations. They should be free from blemishers, cuts, or mechanical injuries.

Grading: Grading is done by hand (i.e. hand grading) or by machines such as screw grader and roller grader (i.e. machine grading). In case of small fruits and vegetables, whole product is graded. In case of medium and large fruits and vegetables, the product can be sliced and these slices can be graded for canning purposes.

Washing and Drying: Washing fruits and vegetables is an important step in canning. This is done to clean the products thoroughly. After washing the products can be air dried.

Peeling: The objective of peeling is to remove the outer layers of fruits and vegetables; not all products require peeling. Peeling may be done in various ways; major types of peeling are:

  1. Hand peeling
  2. Steam peeling
  3. Mechanical peeling
  4. Lye peeling
  5. Flame peeling

Cutting/Slicing: Large and medium fruits and vegetables need to be sliced for canning purposes. Size of the slice is determined by the canning requirements. In case of stone fruits such as mangoes and apricots, seed stones and cores need to be removed before slicing them. Fruits like plums can be canned as whole as it is not easy to extract seeds from such fruits.

Blanching Process: Blanching is the critical process in the entire canning process. Blanching is a brief heat treatment given to the fruits and vegetables before canning them. Major purposes of blanching are:

  1. Reduce microbial activity and contamination of products
  2. Remove undesirable elements from the products
  3. Remove undesirable taste and flavour from foods

Cooling and Filling: After blanching, fruits and vegetables are dipped in cold water for keeping them in good condition. Cooled and air-dried, blanched products are then filled in containers or bottling cans. Before filling them in cans, these containers are sterilized. For can-filling, automatic, can-filling machines may be used. Hand filling is done for small scale canning process.

Syruping and Brining: Syruping is done for fruits while brining is done for vegetables. Syrup is nothing but a concentrated solution of sugar in water; sucrose syrup is used for canning fruits. Syrup is added to canned fruits to improve the flavour and to serve as a heat-transfer medium. Brine is nothing but a concentrated solution of salt in water; brining is done to improve the flavour of canned vegetables and to serve as a heat-transfer medium. Common salt that is iron-free is used for brining purposes.

Exhausting Process: The process of removal of air from cans is known as exhausting. Exhausting is important because:

  1. Corrosion of the tin plate during storage is avoided due to the removal of air
  2. It minimizes discoloration of canned products by preventing oxidation process
  3. It helps in better retention of vitamins and other nutrients present in canned foods
  4. It prevents bulging of cans when stored in a hot climate at high altitudes

Sealing and Cooling of Cans: After filling cans, these containers must be sealed to make them air-tight. A can sealer may be used for sealing cans. In case of containers such as glass jars, a rubber ring should be placed between the mouth of the jar and the lid to make them air-tight. After sealing cans, they need to be cooled. Cooling may be done by any of the following methods:

  1. Dipping in Water: Dipping or immersing the hot cans in tanks containing cold water
  2. Flow of Cold Water: Letting cold water into the pressure cooker specially in case of canned vegetables
  3. Spraying Cold Water: Spraying cans with jets of cool water
  4. Exposure to Cold Air: Exposing the cans to air

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