A pressure canner must be used to safely can low-acid foods. Growth of the bacterium Clostridium botulinum in canned food may cause botulism - a deadly form of food poisoning. Botulinum spores are very hard to destroy at boiling-water temperatures; the higher the canner temperature, the more easily they are destroyed. Therefore, all low-acid foods must be processed at temperatures of 240° to 250°F, attainable with pressure canners operated at 10 to 15 pounds per square inch of pressure as measured by gauge (PSIG). The exact time depends on the kind of food being canned, the way it is packed into jars and the size of jars.
Recommended Pressure Canners for Low-Acid Foods
Today's pressure canner may have a weighted gauge or dial gauge, for indicating and regulating the pressure. Weighted gauges are designed to "jiggle" several times a minutes or to rock gently to maintain proper pressure. Read your manufacturer's directions to know how a particular weighted gauge should function. Dial gauge canners will usually have a counterweight or pressure regulator for sealing off the open vent pipe to pressurize the canner. This weight will not jiggle or rock. The dial gauge measures the pressure. One manufacturer makes a dual-gauge canner; read the manufacturer's user manual for complete instructions.
Three Serious Errors
Three serious errors in temperatures obtained in pressure canners occur because:
- Internal canner temperatures are lower at higher altitudes. To correct this error, increase pressure for your altitude of residence.
- Air trapped in a canner lowers the temperature obtained at 5, 10 or 15 pounds of pressure and results in under processing. All pressure canners must be vente4d 10 minutes before adding the weight to pressurize the canner.
- An inaccurate dial gauge is used. check dial gauges yearly for accuracy. If the gauge reads high or low by more than two pounds at 5, 10 or 15 pounds pressure, replace it.
Know Your Cook-Top
With the advancement of kitchen technology, the smooth cook-top has brought some challenges for canning. Follow the manufacturer's recommendations and consider these issues:
- Some brands of pressure canners are NOT recommended to use on smooth cook-tops. Always follow the manufacturer recommendations.
- Excessive heat reflecting down on the surface can damage the cook-top. Examples are discoloration, burner damage, cracked glass tops or metal fused to the glass top.
- Many of these cook-tops have automatic cut-offs on their burners when heat gets excessive. If burner shuts off during processing, food can be under-processed.
Buying Used Pressure Canners
Old canning equipment can be found at garage sales and auctions. Even though they may appear to be in good shape, many may need replacement parts to make them usable. Many old brands of pressure canners are no longer manufactured. Therefore, finding replacement parts can be impossible. If you are looking to buy a used canner, here are some tips:
- Is the gauge attached or with the canner?
- Is the petcock safety valve complete?
- Are the threads of the opening undamaged?
- Does the seal require a gasket?
- Is the metal to metal seal smooth around lid and bottom with the minute manufactured grooves visible?
- Is the canner "round"? When looking directly into the canner, does it appear to be exactly round and not oblong or bulged in one place? If so, do not use.
- Is the bottom of the canner flat and level? Canners with recessed or rounded bottoms should not be used.
- On wing-screw type canners, check to be sure each screw and corresponding space on lid is in good condition.
Replacement parts are available at a variety of hardware stores, as well as from appliance repair shops, and manufacturers of today's canners websites. such parts may not look exactly light the old part but will serve the same function. Hole diameters and thread size are standard on all makes of canners so new replacements will fit on old canners. Also, many old handles and knobs that have cracked and come off can generally be replaced.