Friday, June 26, 2009

Proper Pressure and Heat Essential for Canning Food Safely

By David Burton
University Extension

In order to be able to assure food safety, meats, poultry, seafood and vegetables should always be canned in a pressure canner according to Tammy Roberts, nutrition and health education specialist, University of Missouri Extension.

Tomatoes and pickled products are the exception because of their acid content.

“Temperatures in a pressure canner reach at least 240 degrees. This high temperature is necessary to assure the safety of the product,” said Roberts.

Pressure canners will have a dial gauge or a weighted gauge. It is important to follow instructions specified for each because they register different pressures at the same setting.

Up to 2,000 feet of sea level, dial gauges are operated at 11 pounds of pressure. Above, 2,000 feet of sea level, adjustments should be made for dial gauges.

A weighted gauge is operated at 10 pounds of pressure at an altitude of up to 1,000 feet. At altitudes above 1,000 feet, higher pressures are needed.

“The reason it is critical to know the altitude at which you are using the pressure canner is because as altitude increases, the temperature at which water boils decreases. Lower boiling temperatures are not as effective at killing bacteria,” said Roberts.

To adjust, processing time or pressure must be increased.

To see a map of sea levels of Missouri Counties, look on the web at

Roberts also recommends that you use jars specifically designed for home canning. Jars that were not designed for canning may not seal properly and may break because they cannot withstand the high temperatures of canning.

“The lids consist of a flat metal disc with a sealing compound around the edge and a band that goes over it to keep it in place. It is important to follow manufacturer’s instructions on preparing the flat for the jar,” said Roberts.

Porcelain-lined zinc lids and bail-type lids used with a rubber ring are no longer recommended.

“The last thing to consider before preparing the food to be canned is the recipe you are going to use. It is critical to use only tested recipes to assure the foods will be safe,” said Roberts.

The Ball Blue Book is a reliable resource. University of Missouri home canning guide sheets are online at The National Center for Home Preservation can be accessed at

There is also still space available in several canning classes being taught in Greene County during the month of July. Call the Greene County Extension Center at (417) 862-9284 or visit the county website at

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