Botulism

In recent months I have found out most people know you get sick from poorly prepared canned foods, but they don't know the reason behind it....well, I picked up a book from the library today with a quick easy understanding of botulism within canned foods.

Botulism poisoning, a very serious and sometimes deadly illness, is most commonly the result of ingesting improperly canned low-acid foods like plain unpickled green beans.  While the bacterium itself is killed by boiling temperatures , its spores survive much higher temperatures than can be achieved in a boiling-water bath and are actually activated in oxygenless environments like the inside of a canning jar.  This means that even though a food has been boiled, processed, and sealed, it may still contain the spores whose activation and growth produce a toxin that can cause botulism poisoning.  The spores cannot, however, survive in high-acid environments-that is, in foods that have a pH lower than 4.6.  Low-acid foods, or vegetables that have not been acidulated (pickled) to a proper degree, must be canned in a pressure canner, which can process jars at temperatures higher than that of boiling water, high enough to kill bacteria as well as the spores of Clostridium botulinum.  Do not process nonacidulated vegetables or meats in anything other than a pressure canner. 

This is not meant to be an inclusive definition of botulism, but a means to clarify why it happens.