Preserving Food:
Using
Pressure Canners
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 pipe in the form of a petcock or covered with
a counterweight, and a safety fuse. Most modern pressure canners are
lightweight, thin-walled kettles; most have turn-on lids fitted with gaskets.
At least one style is still made with heavy cast aluminum, has screw-down knobs
around the canner and does not have a gasket, however.
Modern pressure canners have removable racks, an
automatic vent/cover lock, a vent pipe (steam vent), and a safety fuse. Use
only canners that have the Underwriter’s Laboratory (UL) approval to ensure
their safety.
Today’s pressure canner may have a dial
gauge for indicating the pressureor 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 to indicate that the proper pressure is reached and then maintained
during processing. Dial gauge canners will usually have a
counterweight or pressure regulator for sealing off the open vent pipe 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 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 dual-gauge canner; read the manufacturer’s user manual
for information on when and how to use either the weighted gauge or the dial.
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 the USDA 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 pipe (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 pipe 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 pipe 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. If it is less than two pounds off in accuracy, you
can make adjustments needed to be sure you have the required pressure in
your canner.
Follow these steps for
successful pressure canning:
(Read through all the
instructions before beginning.)
1.
Make sure the pressure
canner is working properly before preparing food. Clean lid gaskets and other
parts according to the manufacturer’s directions; make sure all vent pipes are
clear and contain no trapped material or mineral deposits. Center the canner
over the burner. The burner and range must be level. Your pressure canner can
be damaged if the burner puts out too much heat. In general, do not use on an
outdoor LP gas burner or gas range burner over 12,000 BTU’s. Check your
manufacturer’s directions for more information about appropriate burners.
Put the rack and
hot water into the canner. If the amount of water is not specified with a given
food, use enough water so it is 2 to 3 inches high in the canner. Longer
processes required more water. Some specific products (for example, smoked
fish) require that you start with even more water in the canner. Always follow
the directions with USDA processes for specific foods if they require more
water be added to the canner.
For hot packed
foods, you can bring the water to 180 degrees F. ahead of time, but be careful
not to boil the water or heat it long enough for the depth to decrease. For raw
packed foods, the water should only be brought to 140 degrees F.
2.
Place filled jars, fitted with lids and ring bands, on the jar
rack in the canner, using a jar lifter. When moving jars with a jar lifter, make
sure the jar lifter is securely positioned below the neck of the jar (below the
ring band of the lid). Keep the jar upright at all times. Tilting the jar could
cause food to spill into the sealing area of the lid.
3.
Fasten the canner lid securely. Leave the weight off the vent pipe
or open the petcock.
4.
Turn the heat setting to its highest position. Heat until the
water boils and steam flows freely in a funnel-shape from the open vent pipe or
petcock. While maintaining the high heat setting, let the steam flow (exhaust)
continuously for 10 minutes.
5.
After this venting, or exhausting, of the canner, place the
counterweight or weighted gauge on the vent pipe, or close the petcock. The
canner will pressurize during the next 3 to 10 minutes.
6.
Start timing the process when the pressure reading on the dial
gauge indicates that the recommended pressure has been reached, or, for canners
without dial gauges, when the weighted gauge begins to jiggle or rock as the
manufacturer describes.
7.
Regulate the heat under the canner to maintain a steady pressure
at, or slightly above, the correct gauge pressure. One type of weighted gauge
should jiggle a certain number of times per minute, while another type should
rock slowly throughout the process – check the manufacturer’s directions.
o Loss of pressure at any
time can result in underprocessing, or unsafe food.
o Quick and large pressure
variations during processing may cause unnecessary liquid losses from jars.
IMPORTANT: If at any time pressure goes below the recommended amount, bring the canner back to pressure and begin the timing of the process over, from the beginning (using the total original process time). This is important for the safety of the food.
8.
When the timed process is completed, turn off the heat, remove the
canner from the heat (electric burner) if possible, and let the canner cool
down naturally. (Lift the canner to move it; do not slide the canner. It is
also okay to leave the canner in place after you have turned off the burner. It
is better to do so than to let jars inside the canner tilt or tip over if the
canner is too heavy to move easily.)
While the canner is
cooling, it is also de-pressurizing. Do not force cool the canner.
Forced cooling may result in food spoilage. Cooling the canner with
cold running water or opening the vent pipe before the canner is fully
depressurized are types of forced cooling. They will also cause loss of liquid
from jars and seal failures. Forced cooling may also warp the canner lid.
Even after a dial
gauge canner has cooled until the dial reads zero pounds pressure, be cautious
in removing the weight from the vent pipe. Tilt the weight slightly to make
sure no steam escapes before pulling it all the way off. Newer canners will
also have a cover lock in the lid or handle that must release after cooling
before the lids are twisted off. Do not force the lid open if the cover locks
are not released. Manufacturers will provide more detailed instructions for
particular models.
Depressurization of
older canner models without dial gauges should be timed. Standard size
heavy-walled canners require about 30 minutes when loaded with pints and 45
minutes when loaded with quarts. Newer thin-walled canners cool more rapidly
and are equipped with vent locks that are designed to open when the pressure is
gone. These canners are depressurized when the piston in the vent lock drops to
a normal position. Some of these locks are hidden in handles and cannot be
seen; however, the lid will not turn open until the lock is released.
9.
After the canner is completely depressurized, remove the weight
from the vent pipe or open the petcock. Wait 10 minutes; then unfasten the lid
and remove it carefully. Lift the lid with the underside away from you so that
the steam coming out of the canner does not burn your face.
10.
Using a jar lifter, remove the jars one at a time, being careful
not to tilt the jars. Carefully place them directly onto a towel or cake
cooling rack, leaving at least one inch of space between the jars during
cooling. Avoid placing the jars on a cold surface or in a cold draft.
11.
Let the jars sit undisturbed while they cool, from 12 to 24 hours.
Do not tighten ring bands on the lids or push down on the
center of the flat metal lid until the jar is completely cooled.
12.
Remove ring bands from sealed jars. Ring bands can be washed and
dried and put away for using another time. Put any unsealed jars in the
refrigerator and use first.
13.
Wash jars and lids to remove all residues.
14.
Label jars and store in a cool, dry place out of direct light.
15.
Dry the canner, lid and gasket. Take off removable petcocks and
safety valves; wash and dry thoroughly. Follow maintenance and storage
instructions that come from your canner manufacturer.
Reprinted with permission from the University of
Georgia.
Andress, E. (2011rev.). Preserving Food: Using Pressure Canners. Athens, GA: University of Georgia, Cooperative Extension.
Andress, E. (2011rev.). Preserving Food: Using Pressure Canners. Athens, GA: University of Georgia, Cooperative Extension.
