Pressure canning is the only recommended method for canning meat, poultry, seafood, and vegetables. The bacterium Clostridium botulinum is destroyed in low-acid foods when they are processed at the correct time and pressure in pressure canners. Using boiling water canners for these foods poses a real risk of botulism poisoning.
If Clostridium botulinum bacteria survive and grow inside a sealed jar of food, they can produce a poisonous toxin. Even a taste of food containing this toxin can be fatal.
Boiling food 10 minutes at altitudes below 1,000 ft destroys this poison when it is present. For altitudes at and above 1,000 ft, add 1 additional minute per 1,000 ft additional elevation.
Caution: To prevent the risk of botulism, low-acid and tomato foods not canned according to the recommendations in this publication or according to other USDA-endorsed recommendations should be boiled as above, even if you detect no signs of spoilage. All low-acid foods canned according to the approved recommendations may be eaten without boiling them when you are sure of all the following:
- Food was processed in a pressure canner. Gauge of the pressure canner was accurate.
- Up-to-date researched process times and pressures were used for the size of jar, style of pack, and kind of food being canned.
- The process time and pressure recommended for sterilizing the food at your altitude was followed.
- Jar lid is firmly sealed and concave. Nothing has leaked from jar.
- No liquid spurts out when jar is opened.
- No unnatural or “off” odors can be detected.
Do Your Canned Foods Pass This Test?
- Overall appearance
- Good proportion of solid to liquid Full pack with proper headspace Liquid just covering solid
- Free of air bubbles
- Free of imperfections—stems, cores, seeds
- Good seals
- Practical pack that is done quickly and easily
Fruit and vegetables
- Pieces uniform in size and shape
- Characteristic, uniform color
- Shape retained-not broken or mushy
- Proper maturity
Liquid or syrup
- Clear and free from sediment
Determining Your Altitude Above Sea Level
It is important to know your approximate elevation or altitude above sea level in order to determine a safe processing time for canned foods. Since the boiling temperature of liquid is lower at higher elevations, it is critical that additional time be given for the safe processing of foods at altitudes above sea level.
It is not practical to include a list of altitudes in this post, since there is wide variation within a State and even a county. For example, the State of Kansas has areas with altitudes varying between 75 ft to 4,039 ft above sea level. Kansas is not generally thought to have high altitudes, but there are many areas of the State where adjustments for altitude must be considered. Colorado, on the other hand, has people living in areas between 3,000 and 10,000 ft above sea level. They tend to be more conscious of the need to make altitude adjustments in the various processing schedules. To list altitudes for specific counties may actually be misleading, due to the differences in geographic terrain within a county.
If you are unsure about the altitude where you will be canning foods, consult your county Extension agent. An alternative source of information would be your local district conservationist with the Soil Conservation Service.