Page "Food preservation" Paragraph 21

Lack of quality control in the canning process may allow ingress of water or micro-organisms.

Most such failures are rapidly detected as decomposition within the can causes gas production and the can will swell or burst.

However, there have been examples of poor manufacture ( underprocessing ) and poor hygiene allowing contamination of canned food by the obligate anaerobe Clostridium botulinum, which produces an acute toxin within the food, leading to severe illness or death.

This organism produces no gas or obvious taste and remains undetected by taste or smell.

Its toxin is denatured by cooking, though.

Cooked mushrooms, handled poorly and then canned, can support the growth of Staphylococcus aureus, which produces a toxin that is not destroyed by canning or subsequent reheating.