What canning does

Canning is an important, safe method for preserving food. The canning process involves placing foods in cans or similar containers and heating them to a temperature that destroys micro-organisms that cause food to spoil. During this heating process air is driven out of the can and as it cools a vacuum seal is formed. This vacuum seal prevents air from getting back into the product bringing with it contaminating micro-organisms.

Food spoilage of canned food

Canned food can be spoilt due to faults during processing or canning. Sometimes, spoilage of canned food occurred because of rough handling during transportation, in the warehouse, shops or homes. The dented seams or cans may affect the safety of the food in the can. Therefore, canned food has to be handled with care.

Examine before using them

  • Inspect the can before opening. Metal lids should be firm and flat or curved slightly inward. Check for signs of swollen / bulging lids, dents or cracks.
  • As the jar is opened, notice whether there is an inrush or an outrush of air. Air rushing out or liquid spurting out indicates spoilage.
  • Smell the contents at once. The odour should be characteristic of the food. An “off” odour probably means spoilage (acid, acrid, sour, putrid, etc.)
  • Check the food carefully to see that it has the characteristic texture and colour. Liquids in all foods should be clear. Any change from the natural texture and/or colour may indicate spoilage. DO NOT TASTE ANY QUESTIONABLE FOOD.
  • Check the expiry date. Do not consume the food in the can after the expiry date. (see the list of food that requires date marking).

Canned food storage

  • Practice the rule, FIRST IN, FIRST OUT (FIFO). This means you use the oldest products first. Place the newly purchased cans at the back of the same product already on the shelf.
  • Storage cabinets should be cool and dry. The best temperature for storing canned foods is between 10°C and 20°C. Avoid storing canned food in a warm place or in direct sunlight. Storage time decreases significantly when temperatures are above 24°C. Keep canned foods dry to prevent cans or metal lids from rusting, which may cause cans to leak and food to spoil.
  • Remember that once a can is opened, it becomes perishable; and, if you are not going to eat it right away, transfer the food into another container and should be refrigerator-stored or cooked properly and then stored in the refrigerator. The common practice of allowing the food to remain in the can until it is totally consumed after opening or puncturing it is wrong. It may cause health implications if the food reacts with the metal of the can.
  • Do not freeze your canned food. If you do, keep it frozen until you want to eat it. Freezing the canned food may cause the food inside to expand, causing defect to the seam.

Defects that may cause spoilage of food

Look out for the following defects before buying or using canned food that may cause food spoilage:

  • Peaked Can / Buckled End
    • Metal plate or coating has fractured or the double seam has been distorted.
  • Scrap-In-Die Marks
    • The marks have broken the inner coating, exposing the metal which will react with the content especially with high acidic food.
  • Panelling
    • Generally observed on larger sized containers. Internal coating may fractured or double / side seams distorted.
  • Crushed / Dented
  • Overfill, Flipper, Springer and Swell
    • Overfill, flipper, springer and swell are used to describe cans which have end(s) distended to varying degrees
  • Fractured Seam
  • Corrosion / Rusty
  • Pin-Hole

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