How canning preserves food

The microorganisms that lead to food spoilage need certain conditions to survive: They need water, they need temperatures between about 40°F and 139°F, they need oxygen, and they need a low-acid environment. Most canned preserves and pickles have a water content sufficient to support the growth of microorganisms. So we can’t meet the first condition. Sterilizing the jars and heating the food to boiling for a certain length of time before it’s put into jars kills existing microorganisms, but of course canned foods are meant to be stored at room temperature, which is smack in the middle of the zone most conducive to the growth of new bacteria. So the second condition can’t be met if we want to line up our pretty jars in the pantry. That leaves the last two conditions, which, happily, can be dealt with.