Safe Pressure Canning
Simple Procedures for Safe Effective Pressure Canning
It's canning season, time to store and 'put up' summers bounty. Most people are fine with boiling water bath canning and in most instances it works just swell. Pressure canners can be a tad intimidating for the unitiated, but they do serve a practical purpose.
Pressure canners are best for canning low acid foods like most fresh vegetables and many fruits. The lack of acid in certain food is condusive to deadly bacterial growth that hot water baths and vinegar alone do not allways kill. Pressure canning can kill these deadly bacteria. A pressure canner does not guarantee safe food unless other caveats are adhered to and it is used correctly.
It's not rocket science, it just requires you follow some simple specific guidelines to ensure the safety of food you preserve. The following are the primary steps you should follow when pressure canning.
1 Test your dial gauge every year before using. They are sensitive and can easily be knocked out of kilter from being bumped around or dropped.
2 Altitude. At sea level water will boil at 212 degrees. This is the highest temperature that liquid reaches under normal cooking conditiond, higher than that and it vaporizes and becomes steam. In a pressure canner, the steam is retained nad ubnder pressure which creates an elevated heat neccesary to destroy botulism spores. The pressure needed at sea level is 10 pounds however as the altitude increases, atmospheric pressure decreases throwing off the ratio. Greater pressure is needed at higher altitudes to create the same temperature it did at sea level. Increase pressure by one pound for each 2000 feet above sea level. Adjust pressure for altitude.
3 Vent pressure canners. When you close the lid on a pressure canner, air is trapped inside. This trapped air, in addition to sometimes harboring airborn bacteria will lowers the pressure canners temperature resulting in under processing. To vent a canner, leave the vent port uncovered or manually open petcocks to allow for proper venting. Heat the canner with lid locked into place until water boils and generates steam. When steam flows freely from the vent port or pet cock it is venting, 10 minutes is sufficient. After venting, close the vents or petcock, place the weight over the vent port and seal the pressure canner as per its design to start pressurizing the canner.
4 When using a pressure canner, never lower pressure too quickly. When processing time is completed, remove canner from heat and let stand until the pressure zeroes out. Patience is a virtue.
Up to date research based advice can be found at the National Center for Home Food Preservations website http://nchfp.uga.edu/