How to Use a Pressure Canner to Preserve Foods

COOPERATIVE EXTENSION
THE UNIVERSITY OF GEORGIA
College of Family and Consumer Sciences
in cooperation with the College of Agricultural and Environmental Sciences

Pressure canners for use in the home were extensively redesigned beginning in the 1970's. Models made before the 1970's were heavy-walled kettles with clamp-on or turn-on lids. They were fitted with a dial gauge, a vent port in the form of a petcock or covered with a counterweight, and a safety fuse. Modern pressure canners are lightweight, thin-walled kettles; most have turn-on lids fitted with gaskets. (At least one style has screw-down knobs around the canner and does not have a gasket, however.) They all have removable racks, an automatic vent/cover lock, a vent port (steam vent), and a safety fuse.

Today's pressure canner may have a dial gauge for indicating the pressure or a weighted gauge, for indicating and regulating the pressure. Weighted gauges are usually designed to "jiggle" several times a minute or to keep rocking gently when they are maintaining the correct pressure. Read your manufacturer's directions to know how a particular weighted gauge should rock or jiggle. Dial gauge canners will usually have a counterweight or pressure regulator for sealing off the open vent port to pressurize the canner. This weight should not be confused with a weighted gauge and will not jiggle or rock as described for a weighted gauge canner. Pressure readings on a dial-gauge-only canner are only registered on the dial and only the dial should be used as an indication of the pressure in the canner. One manufacturer now makes a dial-gauge system where either the dial or the weighted gauge may be used.

Pressure canners come deep enough for one layer of quart or smaller size jars, or deep enough for two layers of pint or smaller size jars. The USDA recommends that a canner be large enough to hold at least 4 quart jars to be considered a pressure canner for its published processes.

Serious errors in processes obtained in pressure canners can occur if any of the following conditions exist:

* The altitude at which the canner is operated is above sea level and adjustments in pressure are not made. Internal canner pressures (and therefore temperatures) are lower at higher altitudes. Canners must be operated at increased pressures as the altitude increases. Check reliable canning instructions for altitude adjustments.

* Air is trapped in the closed canner during the process. Air trapped in a pressure canner lowers the temperature obtained for a given pressure (for example, 10 or 15 pounds pressure) and results in underprocessing. To be safe, USDA recommends that all pressure canners must be vented 10 minutes before they are pressurized.

To vent a canner, leave the vent port (steam vent) uncovered (or manually open the petcock on some older models) after you fill the canner and lock the canner lid in place. Heat the canner on high until the water boils and generates steam that can be seen escaping through the open vent port or petcock. When a visible funnel-shape of steam is continuously escaping the canner, set a timer for 10 minutes. After 10 minutes of continuous steam, you can close the petcock or place the counterweight or weighted gauge over the vent port to begin pressurizing the canner. (See steps 3 and 4 below.)

* An inaccurate dial gauge is used. Dial gauges should be checked for accuracy each year before use. If the gauge reads high or low by more than two pounds at 5, 10 or 15 pounds pressure, replace it.

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