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Why can improperly canned foods spoil?
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food preservation
An overview of food preservation.
Improperly canned foods can spoil primarily due to inadequate heat processing, which fails to destroy heat-resistant bacterial spores. When these spores survive the canning process, they can germinate inside the sealed container, multiply, and produce toxins or gases that degrade the food.123
Key factors contributing to this spoilage include:
- Microbial Survival: Bacteria such as Clostridium botulinum, Bacillus, and Clostridium species produce spores that are highly resistant to heat. If the food is not heated to a sufficient temperature—typically above 100 °C (212 °F) and often up to 120 °C (248 °F) for low-acid foods—these spores remain viable.1243
- Anaerobic Conditions: The vacuum-sealed environment of a can creates an anaerobic (oxygen-free) atmosphere, which is ideal for the growth of C. botulinum and the subsequent production of the deadly botulinum toxin.43
- Chemical and Physical Changes: Microbial activity can lead to "flat sour" spoilage, putrefaction, or gas production, which may cause cans to bulge or burst.12
For safety, any canned food showing signs of bulging or abnormal odor, appearance, or taste should not be consumed, as it may contain dangerous toxins.32