On Food and Cooking

isolated in hermetically sealed containers. The
heat deactivates plant enzymes and destroys
harmful microbes, and the tight seal prevents
recontamination by microbes in the
environment. The food can then be stored at
room temperature without spoiling.
The arch villain of the canning process is
the bacterium Clostridium botulinum, which
thrives in low-acid, airless conditions —
oxygen is toxic to it — and produces a deadly
nerve toxin. The botulism toxin is easily
destroyed by boiling, but the dormant
bacterial spores are very hardy and can
survive prolonged boiling. Unless they are
killed by the extreme condition of higher-
than-boiling temperatures (which require a
pressure cooker), the spores will proliferate
into active bacteria when the can cools down,
and the toxin will accumulate. One
precautionary measure is to boil any canned
produce after opening to destroy any toxin
that may be there. But all suspect cans,