Canning involves heating food to a temperature hot enough to kill harmful bacteria and then sealing the container to keep air and other bacteria out. Once bacteria have been reduced or eradicated, canned food can be kept for long periods of time without spoiling. Though canned goods can last for years, improper handling could shorten their life.
When canned goods are kept at temperatures above 95 degrees Fahrenheit, the chance of spoilage increases. For commercially processed foods, heat encourages the growth of any bacteria that might have remained after the canning process. For home-canned foods, heat also can compromise the seal. Food expands as it heats. That expansion increases the force on the inside of the lid, loosening it from the jar. Even small amounts of air from the outside can bring in unwanted microorganisms, which can cause spoilage.
An increase in temperature also can cause nutrient loss. Heat destroys some vitamins, most notably vitamins A and C. Consequently, some vitamins are invariably lost during the canning process. In addition, according to Utah State University food safety specialist Brian A. Nummer, canned goods lose 5 to 20 percent of vitamins A and C every year just from sitting on the shelf. Storing them at temperatures above 75 F accelerates that loss.
Avoid storing foods in places warmer than 75 F. High cabinets, cabinets near ovens, stoves or furnaces, cabinets that have hot water pipes running under or through them, or cabinets in the attic are bad places for canned goods. Also problematic for canned goods are places with large temperature fluctuations -- the garage, for example. Avoid storing canned goods in direct sunlight. Not only can sunlight heat up the contents of cans, it also can destroy nutrients in food stored in translucent jars.
The ideal storage place for canned goods is a cool, dry and dark place. Aim for stable temperatures between 50 and 70 F. Develop a "first in, first out" storage system that lets you use your oldest food first. Doing so minimizes the damage caused by either slightly high temperatures or prolonged storage.
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