How to Safely Use a Pressure Canner
Pressure Canner vs. Pressure Cooker
Low-acid foods must be processed at a temperature that is hotter than boiling water. Compared to water bath canning or steam canning, which processes jars at 212ºF, a pressure canner processes at 240ºF, the necessary temperature for destroying food spoilage organisms in foods with a pH greater than 4.6. Such low-acid foods include poultry, seafood, meats, and most vegetables. Although a pressure canner is more expensive, it is more versatile because it may be used for boiling water canning and for pressure canning.
Three of the four major pressure canner brands — Granite Ware, Mirro, and Presto — are lightweight, relatively inexpensive, and made in China. The All American brand is considerably heavier, and therefore more durable as well as more expensive, and is made in the United States. All models are made of aluminum, which is an excellent conductor of heat.
The bad news for anyone who uses an induction cooktop is that aluminum is not magnetic, therefore is not suitable for use on an induction cooktop. Pressure canning may be an issue for any smooth surface cooktop, because of the canner’s weight and the high temperature a pressure canner generates.
All pressure canners feature:
1) Securely locking cover
2) Vent pipe coming through the cover
3) Weighted pressure regulator that fits over the vent pipe,
4) Overpressure safety device that automatically releases steam (should the vent pipe get clogged and fail to function).
5) Most pressure canners also come with either a flat perforated metal rack or the same type of wire rack used for water bath canning. The rack elevates jars above the canner bottom to prevent breakage and to allow steam to circulate during processing.
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The goal of all pressure canners is to produce pressurized steam that generates a high enough temperature for the safe home processing of low-acid foods. The mechanics, however, differ among the brands, which is potentially confusing for the first-time buyer. To complicate things, canners made before about 1970 differ slightly from modern canners. If you acquire an older pressure canner, may you be lucky enough to also acquire its instruction manual.
Canners are sized according to the capacity of the amount of water they’ll hold. How many jars the canner will process at one time depends on the canner’s diameter and height. The smallest pressure canner is the All American 10-quart model, which will process 4 one-quart jars and 5 to 7 pint jars, depending on whether the pints are wide or narrow mouth.
The most popular models have a capacity of between 15 and 21 quarts, and will process 7 one-quart jars at a time, or 8 or 9 pints. Some canners are tall enough for double stacking, meaning they will process two layers of pint-size jars, one on top of the other. If you’re looking at a tall canner, and the clearance above your range is limited, check to make sure the canner will fit. The largest pressure canner — designed for really serious canning — is the All American 41-quart model. It is 19 inches tall and the only model that may be used to double stack quart-size jars. In one load it will process 19 quart jars, or 32 to 36 pints.
For double stacking, a flat perforated metal jar rack must be placed on top of the first layer of jars before the second layer is added. The rack stabilizes the second layer so the jars can be staggered for good steam circulation and so they will remain upright throughout the canning process; the perforations allow steam to circulate freely. Some pressure canners come with a flat perforated rack, and such racks are readily available in a range of sizes. You might also repurpose something similar, such as a round cake cooling rack.
All low-cost pressure canners use a rubber or silicone gasket to form a tight seal between the canner and the cover. The gasket, also called a sealing ring, should be removed from the cover, washed, and inspected at the beginning of each canning season and after each use. Most manufacturers recommend periodically lubricating the gasket to keep it pliable.
Eventually, the gasket will need to be replaced because it has stretched, dried out, cracked, cut or is otherwise damaged. Replacing the gasket at the end of each canning season, or at least keeping a spare on hand, is always a good idea.
The gasket that came with my first pressure canner lasted many years. Eventually, it stretched so much I couldn’t insert it back into the cover, so I bought a new gasket. That one didn’t last through a single season, leaving me in the middle of a canning job with no readily available gasket. So I learned the hard way to keep a spare.
All American canners are gasket-free. The cover clamps directly to the canner by means of a series of wing nuts, creating a metal-to-metal seal — no gasket to fail at the worst time. Since our family relies on homegrown and home processed foods, I decided to get one of these canners. Initially, I had trouble removing the cover from my new canner. Then I read the instructions and learned the canner rim should be lubricated with petroleum jelly to keep the cover from sticking. From then on I had no more trouble removing the cover.
The cover of every pressure canner has a vent pipe, also called a vent port or steam vent. It’s a short tube that extends through the canner cover and above the cover. Its purpose is to vent air from the canner to allow the canner to pressurize. Once the canner has been vented, the vent pipe is closed with a pressure regulator placed on top to slow the escape of steam.
Most canners have an adjustable pressure regulator, sometimes called a weighted gauge, that may be set for a pressure of five, 10, or 15 pounds per square inch (psi). At sea level, 10 psi will result in the canning temperature of 240ºF necessary for the safe processing of low-acid foods. At elevations above 1,000 feet, water boils at a lower temperature, requiring a psi of 15 to achieve a minimum canning temperature of 240ºF.
Among veteran home canners, the pressure regulator is called a jiggler. When the correct pressure is reached and maintained, the regulator periodically releases small amounts of air and steam, causing it to jiggle and make a characteristic sound that canners learn to listen for. Your model’s manual will tell you if the jiggler should rock steadily throughout the canning process or if it should jiggle a certain number of times per minute.
The pressure regulator on a Presto canner is not adjustable. To distinguish it from an adjustable regulator, it’s sometimes called a counterweight. Its purpose is to release pressure above 15 psi, at which time the regulator will warn you by jiggling. Pressure is measured by a pressure gauge that has a dial with an indicator pointing to the canner’s internal pressure. The amount of pressure is adjusted entirely by the amount of heat applied to the canner — the higher the heat, the greater the pressure.
When using a Presto or a canner that is entirely regulated with a pressure gauge, at sea level the pointer on the dial should be at 10.5 psi to achieve a safe canning temperature of 240ºF, although 11 psi is often recommended because it’s easier to read on the dial. At elevations above 2,000, the pressure must be increased by one pound per additional 2,000 feet to maintain the same temperature.
All American brand canners have both an adjustable pressure regulator and a pressure gauge. The regulator controls the pressure and the gauge provides assurance that the pressure is correct. The real advantage to the gauge is, at the end of each canning session, you can tell when the canner has been completely depressurized, so you can safely remove the regulator and open the cover. Do not unscrew the wingnuts until the dial reads zero pressure, which takes about 30 minutes for pints or 45 minutes for quarts. Then remove the pressure regulator before loosening the wing nuts.
Granite Ware, Mirro, and Presto canners have cover locks that prevent the cover from being lifted while the canner is under pressure. Because all three brands are thinner than All American canners, they cool faster and depressurize more quickly.
Every pressure canner has an overpressure safety device, sometimes called a fuse, that releases excess pressure if the vent pipe gets clogged or otherwise isn’t working properly. Most canners have a simple overpressure plug consisting of a rubber stopper that pops up when it needs to release steam. The overpressure plug should be replaced whenever it gets hard, deformed, or cracked. If the canner has a gasket, replace the overpressure plug whenever you replace the gasket. The Granite Ware canner, instead of having an overpressure plug, has two metal overpressure valves, one whistles a warning.
All American: allamericancanner.com
Granite Ware: graniteware.com/graniteware-canning
A dandy website where you can see and compare all the major pressure canner models in one place is www.pressurecooker-outlet.com/Pressure-Canners.htm. This site also offers a full line of replacement parts, including flat perforated racks in various sizes, and provides answers to many common questions about pressure canning.
The National Center for Home Food Preservation includes a page on pressure canning at nchfp.uga.edu/publications/uga/using_press_canners.html
Testing Your Pressure Gauge
Although many canning manuals suggest you periodically have your gauge checked, you’ll have a hard time finding anyone to do it. But you can test your own gauge.
For a Presto, put a quart of water into the canner, vent the canner, and bring the pressure up until the pressure regulator jiggles. If the needle on the dial is pointing to 15 psi, it’s accurate. If the gauge is off by less than two psi in either direction, you can compensate by adjusting the pressure during processing (increase if the gauge reads low, decrease if it reads high). If the gauge is off by more than two psi, replace it.
The main function of the pressure gauge on an All American canner is to show when the canner has been depressurized at the end of processing. The processing pressure is accurately controlled by the three-way pressure regulator, which does not need testing or replacement.
Before processing food, such as canning green beans, in a new pressure canner, do a trial run with just water (no jars) in the canner — bring up the pressure, note what it takes to keep the pressure steady on your range, and then depressurize — so you can become familiar with how your particular canner operates. Each brand of pressure canner has a specific recommended procedure to follow. Refer to your owner’s manual for details. In general, pressure canning involves the following steps:
- Put the canner on the burner, place the rack in the bottom of the canner, and add the amount of water specified in the recipe, usually about three inches. Turn the burner on low to keep the water hot, but not boiling; setting a glass jar into boiling water may cause the jar to crack.
- Fill hot, clean jars according to the recipe. Reliable recipe booklets filled with food preservation examples come with most canners, or may be found online at such sites as nchfp.uga.edu and freshpreservingstore.com. Use your jar lifter to place filled jars, fitted with lids and bands, on the rack in the canner.
- Place cover on the canner and fasten securely. Do not put the pressure regulator on the vent pipe.
- Turn the heat to the highest setting until steam flows freely from the open vent pipe. You should be able to see steam being released and hear it hiss. Leaving the heat on high, set your timer for 10 minutes while the canner vents to exhaust air from the canner, as indicated by steam steadily flowing through the vent pipe.
- After 10 minutes, place the pressure regulator on the vent pipe. If your canner has an adjustable pressure regulator and you are at an elevation of 1,000 feet or less, set the regulator to 10 psi. If your elevation is above 1,000 feet, set the regulator for 15 psi.
- Adjust the heat to maintain adequate pressure. If your canner has no pressure gauge, rapidly heat the canner until steam begins to escape from the pressure regulator, causing the regulator to jiggle or hiss, then reduce the heat just enough to maintain a steady pressure. If your canner has a pressure gauge, when the dial reaches two pounds less than the desired pressure, turn the heat down so the pressure gradually rises to the required setting. Any rapid or wide variation in pressure can cause liquid to leak from jars, called siphoning, which results in failed seals.
- Within three to 10 minutes, depending on the size of the canner and how many jars you are processing, the correct pressure will be reached. When the pressure is holding steady — as indicated by the sound of the pressure regulator on the vent pipe, or by the needle on the dial gauge — set your timer according to the required processing time for the specific food you are canning. If at any time during processing, the pressure in the canner goes below the recommended amount, bring the pressure back up and reset your timer for the full processing time to ensure safe processing.
- When the processing time is up, turn off the heat. Most instructions recommend removing the canner from the burner. I don’t because I can’t lift a full canner. And sliding a canner across the stove can ruin the cooktop or a burner.
- Here’s the hard part: Walk away and let the canner naturally cool until it has fully depressurized. Do not attempt to speed up cooling, and do not remove the pressure regulator from the vent until the pressure is all the way down. The canner has fully depressurized when the overpressure plug has dropped, the cover lock (if your canner has one) has released, the dial on the pressure gauge (if your canner has one) points to zero, and no steam escapes when you gently nudge the pressure regulator on the vent pipe.
- After the canner has completely depressurized, remove the pressure regulator from the vent pipe. Wait another 10 minutes before unfastening and removing the cover. Do not wait for the canner to cool completely or you may have trouble removing the cover. Always lift the cover away from your face to avoid getting burned by rising steam.
- Use your jar lifter to remove the jars one by one without tilting them. Place the jars, one-inch apart, on a rack or thick towel away from drafts.
- Let the jars cool for at least 12 hours before removing the bands and testing the seals.
Adjust processing pressure according to your elevation.
|At this elevation:||Dial gauge:||Pressure regulator:|
|0 – 1,000 feet||11 pounds||10 pounds|
|1,001 – 2,000 feet||11 pounds||15 pounds|
|2,001 – 4,000 feet||12 pounds||15 pounds|
|4,001 – 6,000 feet||13 pounds||15 pounds|
|6,001 – 8,000 feet||14 pounds||15 pounds|
|8,001 – 10,000 feet||15 pounds||15 pounds|
|You can find your elevation by entering your zip code at this website: http://www.daftlogic.com/sandbox-google-maps-find-altitude.htm|
Pressure Canner Care
Wash and dry your pressure canner after each use. Leaving food residue in the canner may cause it to absorb odors and can pit the aluminum. Before and after each use, wash and dry the cover, paying close attention to the edges of the cover, the vent, and the safety plug or valves.
If your canner has a pressure gauge, take care not to get water into the dial. Do not immerse the gauge in water, and do not set the cover upside down while it is wet (including when you first open the canner after each processing session).
If your canner has a gasket, remove it from the cover, wash and dry it, and inspect it for damage. Also, make sure the vent pipe is free of obstruction by holding the cover up to a window or light and looking from the inside of the cover through the vent pipe hole. Clear the vent pipe of any obstruction if necessary.
At the end of each season, thoroughly wash and dry the canner before storing it. Do not seal the cover on the canner, but instead place it upside down on the canner so air can circulate and, if the canner has a gasket, to prevent the gasket from remaining compressed during storage.
If your canner has a pressure gauge, do not set the cover upside down at any time the inside cover is wet.
Pressure Canner as Water Bath or Steam Canner
If your pressure canner is tall enough to hold a sufficient amount of water to cover jars by at least two inches, with another two to three inches of air space to prevent water overflow, you may use your pressure canner as a water bath canner for processing high-acid foods. Simply follow your recipe directions exactly as you would process the high acid food in a boiling water canner, but do not put the pressure regulator on the vent pipe at any time during processing. Also, do not lock down the pressure canner’s cover on all brands except the All American. For the All American, keep the cover in place by screwing down two opposite wingnuts.
Bring the water inside the canner to a full boil. When the water is boiling, as indicated by steam flowing steadily from the vent pipe, set your timer for the correct processing time specified for whatever high acid food you are canning. As long is steam is streaming from the vent, the water is boiling.
When the processing time is up, turn off the heat and let the canner cool down until steam no longer hisses from the vent pipe. Then remove the cover and continue as you normally would when using a standard water bath canner.
If your pressure canner is large enough, jars may be double stacked for water bath canning the same as for pressure canning. The reason it’s not commonly done in standard water bath canners is that the canners are generally not tall enough to accommodate two layers of jars with sufficient water to cover plus air space to prevent water from boiling over onto the stovetop.
Can a pressure canner be used for atmospheric steam canning? The jury is still out. Although home canners are doing it, no one official has deemed it safe. According to professor Barbara Ingham, who led the University of Wisconsin team that proved the safety of steam canning, approval of the use of a pressure canner for steam canning requires researching both steam distribution within the canner and the ability of the canner to effectively vent out air. More to the point would be to determine a suitable and safe procedure for using a pressure canner as a steam canner.
Counterweight – A pressure regulator that is not adjustable.
Double Stacking – Processing two layers of jars at a time, also called double decking.
Gasket – A flexible rubber or silicone ring that fits inside the canner cover and forms a pressure-tight seal between the canner and the cover during processing; also called a sealing ring.
Overpressure Device – A rubber plug or safety valve in the canner cover that automatically releases steam if excess pressure cannot be released normally through the vent pipe; also called a safety fuse.
Metal-to-Metal Seal – A pressure canner cover that does not use a gasket to create a tight seal.
Pressure Canner – A pressurized vessel that raises the temperature to 240ºF (28ºF above the temperature of boiling water) for the safe canning of low acid foods.
Pressure Regulator – A weighted device placed over the vent pipe to allow pressure to increase inside the canner, and which periodically releases small amounts of steam and air to maintain the pressure.
psi – Pounds per square inch, the unit used to measure pressure in a canner.
Siphoning – The leaking of liquid from jars during processing, usually resulting from a too rapid drop in pressure either as the canner reaches pressure and heat is turned down too low, or the time is up and the canner cools too fast.
Venting – To release air from the pressure canner and jars so the canner can pressurize; also called exhausting.
Vent Pipe – A short tube through the cover of a pressure canner that releases air from inside the canner to allow the canner to pressurize; also called a vent port or steam vent.
Weighted Gauge – An adjustable pressure regulator.
A Pressure Cooker is Not a Canner!
Although several pressure cooker brands are promoted as being suitable for canning, a pressure cooker is not the same as a pressure canner. A pressure cooker, sometimes called a pressure saucepan, similarly uses steam under pressure to cook meals fast but is generally smaller than a pressure canner. The USDA recommends that a vessel large enough for safe pressure canning must hold at least four quart-size canning jars, which requires a liquid capacity of 10 to 12 quarts compared to the standard six to eight-quart pressure cooker. (A pressure canner certainly may be used as a pressure cooker, if you don’t mind cooking food directly in an aluminum pot, but for most situations the sheer size of a pressure canner makes pressure cooking somewhat cumbersome.)
The larger size of a pressure canner allows the canner to attain stable processing times, temperatures, and pressures that are suitable for the safe preservation of vegetables, meats, and other low acid foods. The amount of time required for the canner to reach processing pressure and the amount of time needed to cool naturally and return to zero pressure are necessary aspects of safe pressure canning. Because a pressure cooker contains less metal and holds less water, it reaches pressure and reduces pressure more rapidly than occurs in a pressure canner, potentially resulting in under processed and therefore unsafe canned foods. Further, a pressure cooker is typically cooled under running water to get the pressure down quickly, which never should be done with a pressure canner. Not only does such rapid cooling result in unsafe processed food, but it may permanently damage your canner.
Unlike aluminum pressure canners, some pressure cookers are made of stainless steel. As tempting as it might be to have a multi-purpose cooker/canner made of non-reactive steel, aluminum is a much better conductor of heat and therefore is more suitable for pressure processing food in jars. On the downside, an aluminum canner is non-magnetic, making it inappropriate for use on an induction cooktop.
Do you use a pressure canner for your food preservation on the homestead? Let us know what advice you have for folks that are new to pressure canning?