canning

Canning Process Overview

Definition of Canning

Canning is the process of preserving fruits and vegetables from the destruction caused by spoilage organisms within hermetically sealed containers through the application of heat. This method is defined as the preservation of food in permanent, hermetically sealed containers (which can be made of metal, glass, thermostable plastic, or multilayered flexible pouches) utilizing heat to inhibit the growth of microorganisms. Introduction of heat is critical because it destroys harmful microorganisms, and the permanent sealing of cans prevents re-infection after the sterilization process.

Historical Background

The concept of canning is often attributed to Nicolas Appert, who invented a method of hermetically sealing foods in containers followed by heat sterilization in 1804 in France. Thus, canning is frequently referred to as "appertising" in honor of Appert's contribution to modern preservation techniques.

Diagram of Canning Equipment

Figure 1: Labelled Diagram of Canning Retort
  1. Retort Body
  2. Retort Bottom
  3. Cover
  4. Screws
  5. Tightness Cover
  6. Closing Device
  7. Weight
  8. Bubbling Device for Steam
  9. Articulated Arm for Cover
  10. Pans with Recipients
  11. Plates
  12. Closing Device

Advantages of Canning

Canning offers an efficient means of preserving food without the use of chemical preservatives. The process utilizes heat treatment at significantly high temperatures to eliminate microorganisms such as bacteria, yeasts, and molds, followed by a hermetic seal to prevent contamination. Key benefits include:

  1. Long Shelf Life

    • Canned fruits and vegetables are free from preservatives. The heat treatment combined with sterile containers ensures that spoilage-causing microbes are destroyed, resulting in an extended storage life.

  2. Nutritional Value

    • Research suggests that canned foods possess nutritional qualities comparable to, or exceeding, fresh foods, provided they are handled correctly from the harvest stage.

  3. Tamper Resistance

    • Cans possess significant resistance to tampering. Signs of damage such as rust, dents, or bulging indicate potential safety risks to consumers.

  4. Food Safety

    • The canning process involves heating that kills bacteria and is performed shortly after harvesting to preserve maximum flavor and nutritional value. Canned products should be used immediately after opening to maintain quality.

Flow Chart for Canning Process

The canning process consists of several sequential steps:

  1. Selection of Fruits/Vegetables
    • Fresh, ripe, and uniformly mature fruits/vegetables are chosen.
  2. Grading
    • Items are graded based on size and color.
  3. Washing
    • Products are washed to eliminate any pesticide residues and dust.
  4. Peeling
    • The outer layer is removed as necessary.
  5. Cutting
    • Fruits/vegetables are cut into desired sizes, and seeds, stones, and cores are removed.
  6. Blanching
    • This involves a mild heat treatment by plunging the products in water at temperatures of 180-200 °F for approximately five minutes.
  7. Cooling
    • After blanching, items are dipped in cold water to facilitate handling.
  8. Filling and Syruping/Brining
    • The fruits/vegetables are filled into cans at temperatures of 79-82 °C with a headspace of 0.3-0.5 cm.
  9. Exhausting
    • Air is removed from the cans.
  10. Sealing
    • Cans are sealed airtight using a can sealer.

Canning Process Steps

Further Process Steps:
  1. Processing
    • Cans undergo heating in boiling water at (100ext°C)(100^{ ext{°C}}) for preservation.
  2. Cooling
    • To prevent further cooking, the cans are cooled rapidly to about (39ext°C)(39^{ ext{°C}}).
  3. Storage
    • Canned products should be stored in a cool and dry environment.

Canning Equipment

Key equipment used in the canning process includes:

1. Can Body Reformer

  • Function: Reshapes collapsed can bodies for efficient transportation into a cylindrical form.
  • Capabilities: A rotary reformer operates at a speed of 10 to 15 cans per minute, powered by a 1 HP motor operating at 1440 RPM.
  • Construction: Made with high-quality materials designed for low maintenance and corrosion resistance.

2. Flanger

  • Function: Used to seam the tops and bottoms of the can body.
  • Construction: Manufactured from high-grade stainless steel with a worm gear & drive mechanism.
  • Features: Two flanging dies including grooves for proper sealing.

3. Double Seaming Machine

  • Function: Closes can ends.
  • Capacity: Approximately 60 cans per hour.
  • Motor Specification: Equipped with a 1 HP, 3-phase 440 volts motor.
  • Process: Involves two operations - rolling the lid flange under the body flange and tightly pressing all five layers of tin plates together while maintaining vacuum conditions.

4. Exhaust Box

  • Purpose: Removes air from filled cans prior to seaming.
  • Capacity: Can process two A 2 ½ cans simultaneously.
  • Operation: Available in three speed settings (high, medium, low), powered by a 1.5 HP motor with a total length of 18 ft.
  • Benefits:
    • Prevents corrosion of tinplate and oxidation, which can cause discoloration.
    • Enhances retention of nutrients such as Vitamin C.
    • Reduces chemical reactions between containers and contents and minimizes excessive pressure build-up during sterilization.
    • Typical exhausting method involves submerging cans in hot water at temperatures ranging from (82ext°C)(82^{ ext{°C}}) to (100ext°C)(100^{ ext{°C}}) for a duration of 6-10 minutes.

5. Retort

  • Function: Used for sterilization of sealed cans under steam pressure.
  • Construction: A cylindrical body fabricated from mild steel with dished end tops and perforated connections for steam/water.
  • Capacity: Generally designed to accommodate around 250 cans, each with a diameter of 401 with thick plates.
  • Procedure: Cans are sterilized when water begins boiling, marking the start of the timing for the sterilization process.