Visual examination of commercially sterile low-acid and acidified low-acid foods packed in hermetically sealed containers

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1.0 Introduction

The presence of a serious container defect can compromise the safety of hermetically sealed packages of low-acid and acidified low-acid foods. A visual examination can be used to verify the integrity of the hermetically sealed packages.

2.0 Definitions

For the purpose of this document the following definitions apply.

Canned Food:

A commercially sterile low-acid or acidified low-acid food packed in hermetically sealed containers.

Serious Metal Can Defect:

Any hermetically sealed metal can that:

  1. is swollen;
  2. shows evidence that the hermetic seal is lost or seriously compromised; or
  3. is unsuitable for distribution and sale as stipulated in the Food and Drugs Acts Section 4 and/or section 27.003 and 27.005 of the Food and Drug Regulations.

3.0 Equipment

The following equipment is commonly used during a visual examination:

4.0 Sampling

4.1 Sample Size

The compliance of a lot can be assessed by examining a total of 200 containers from throughout the lot.

4.1.1 Selection of Containers

A representative sample of the lot can be obtained by using the following sampling plan:

Number of Containers Per Case Number of Cases from which to select containers Number of Containers to select per Case
5 or less 40 all
6-12 34 6
13-60 17 12
61-250 13 16
251 or more 9 24

Example:

For cases that hold 24 containers:

  • 17 cases would be selected randomly
    • 12 containers would be selected from 16 cases and 8 containers from the 17th case for a total of 200 cases.

Note: For lots having less than two hundred containers, all of the containers would be examined.

5.0 Examination Process

5.1 Cases

Examine the cases selected for the presence of wet stains or damage. When there are cases affected, examine the cases in close proximity and all the containers in the affected cases for damage and to determine the source of the wet stains.

5.2 Label Removal

The labels should be removed from all containers examined.

  • Remove the labels from all 200 containers to allow for a thorough examination of the containers.
  • When a defect and the relationship to the label are important, mark the label so that it can be placed in the same position on the container prior to its removal.
  • Examine the inside surface of the labels removed for the presence of stains.
  • Examine the containers as outlined in section 4.2 of Metal Can Defects - Identification and Classification
    • Refer to the Metal Can Defects Identification and Classification document which outlines the various metal can defects.
  • Examine the containers or labels for the presence of a code or lot number that identifies in a legible and permanent manner:
    • the establishment in which the product was rendered commercially sterile, and
    • the day, month and year on which the food was rendered commercially sterile

5.3 Teardowns

Select a sub-sample of at least 6 containers, from the 200 containers sampled, to conduct a seam teardown and cross-section as outlined in section 4.1 of the Metal Can Defects Identification and Classification.

6.0 Wet, Stained or Damaged Cases

When wet spots, stains or damage to cases are the result of:

  1. Swollen or leaking containers:
    • refer to section 7.1
  2. Physical damage to cases and/or containers (e.g. forklift), or other damage (e.g. water damage, leakage from another lot):
    • segregate the wet, stained or damaged cases from the lot
      • remove damaged containers from sale and distribution.

7.0 Metal Can Defects

7.1 Swollen or Leaking Containers

Containers that are swollen, not properly sealed or has any defect that may adversely damage its hermetic seal cannot be sold (section B.27.003 of the Food and Drug Regulations.)

Determine whether the cause for the swelling or leaking is:

  • post-process contamination as a result of container damage or a seam defect
  • inadequate thermal treatment
  • overfill

7.1.1 Swelling due to overfill

  • is a serious defect because it can compromise the effectiveness of the thermal treatment.
    • the affected containers can be removed from the lot and the remaining containers are eligible for sale and distribution

7.1.2 Swelling due to a visible container defect, or container damage

  • is a serious defect
    • the affected containers can be removed from the lot and the remaining containers are eligible for sale and distribution

7.1.3 Swelling with no visible container defect or damage:

  • Test the containers for the presence of bacteria using a method shown by evidence to be effective.
    • The types of bacteria present in the container provide information on whether the swelling is the result of post-contamination or inadequate thermal processing. Methods are available in Health Canada's Compendium of Analytical Methods.
  • Swelling due to inadequate thermal processing is a serious defect.
    • the entire lot is not fit for sale or distribution
    • review the scheduled process developed and applied
  • Swelling due to post-contamination indicates that the hermetic seal of the container has been either lost or compromised so it is a serious defect.
    • it is not possible to identify all containers that may be affected but have not yet become swollen therefore the entire lot is not fit for sale or distribution

8.0 Mechanical Screening

Mechanical screening using a double dud detector (DDD) and checkweigher, is an alternative method that can be used instead of the Visual Exam for canned salmon.

The checkweigher weighs all of the cans in a lot and is set to eject cans at or below an underweight set-point, and cans at or above an overweight set-point.

  • Ejected underweight cans may have leaked during the process but may still have maintained a vacuum (e.g., a pin hole that may be sealed by coagulated protein).
  • Ejecting overweight cans allows the DDD to sample cans with low end deflections due to low vacuum rather than excessive weight.

The double dud detector is set to:

  • reject all cans with end deflections below the minimum set-point or zero vacuum, and
  • select a sample of cans most likely to contain defects, for example: lowest vacuum, for a visual examination.

9.0 Results

Serious defects are those that can compromise or result in the loss of the hermetic seal. Containers with a serious defect are not fit for sale or distribution.

The presence of one or more serious defects indicates a deviation from the critical limits of a critical control point (CCP) at the seam closure steps, or the retort process (in the case of a swollen container due to an inadequate thermal treatment).

  • Corrective actions are required to ensure the CCP is brought under control.
  • Any product produced at the time the deviation occurred is potentially unsafe.

Minor defects are those that do not compromise or result in the loss of the container integrity (hermetic seal) and do not present a risk of contamination of the food. Containers with minor defects are eligible for sale and distribution.

  • The presence of minor defects is an indication that certain control measures may be ineffective or not properly applied. For example, crushed or rusted containers is a sign that there may be issues with the storage and handling conditions.
  • A minor defect within the seam is a sign that the controls at the seam closure step are moving away from the critical limits. Additional monitoring actions may be needed to ensure the parameters remain within critical limits.

10.0 References

Metal Can Defects - Identification and Classification Canadian Food Inspection Agency.

Low-Acid and Acidified Low-Acid Foods In Hermetically Sealed Containers, Health Canada

Compendium of Analytical Methods. Evaluation Division, Bureau of Microbiological Hazards, Food Directorate, Health Products and Food Branch, Health Canada.

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