Yeasts, molds, and most live bacterial cells are the most common spoilage organisms associated with acid foods. These are easily destroyed in foods adequately heated in a boiling water canner. Boiling water canners operate at around 212 degrees F., even though the actual temperature will depend on one's altitude. The acidity controls for the risk of botulism poisoning, which is a concern in low-acid canned foods like vegetables and meats.
Low-acid foods, such as green beans, must be processed in a pressure canner. Higher temperatures than boiling water are required to kill the naturally occurring spore form of ''Clostridium botulinum'', the microorganism that causes the potentially fatal botulism poisoning. There is not enough natural acid to control the development of toxin in these foods, so heat must be used to kill the spores.
