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11.1.4 I got this pressure canner (not cooker!) for a gift. How do I take care of it?




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This article is from the Food Preserving FAQ, by Eric Decker ericnospam@getcomputing.com with numerous contributions by others.

11.1.4 I got this pressure canner (not cooker!) for a gift. How do I take care of it?

From: phillips@colum.edu (Gary Phillips x397)
The two largest US manufacturers of pressure canners for home use are Mirro
and Presto. I imagine their products are available in Canada and if you can
find a hardware or cooking supply store that handles either brand they will
be able to special order these items for you even if they don't have them in
stock.

My present canner is a Mirro. It does 7 quart jars at once, operates at a
choice of 5, 10, or 15 psi, and cost me about $50 in US currency six years
ago. It was the least expensive model offered by a local hardware store from
stock, and prices went up from there to as high as $100. It has been well
worth the investment.

Do NOT buy a pressure *cooker* for canning. Although most of them purport to
be suitable for doing a few jars (3 or 4) at a time, in fact they can't hold
the temperature and pressure evenly enough for really safe operation.
[ lack of thermal mass -- ED]

From: phillips@colum.edu (Gary Phillips x397)
>Yes I bet...I would love to find one at a garage sale. BTW if I ever do,
>do you know what to look for to make sure it is still operating safely?

Sure. Check the rim of both pan and lid to make sure there are no nicks or
damage to the interlocking tabs. Make sure the safety pressure release
(usually a rivet-like rubber plug) is still present and soft and moving
freely in its slightly oversized hole. Check the gasket that goes between
pan and lid for cracks or hardening. Make sure the pressure vent is clean
and open, and that the seat for the pressure release weight is smooth and
fits well. If there is a pressure gauge, it MUST be recalibrated.
Contact the manufacturer for information about that. It would probably be a
good idea to order a new gasket and a safety release at the same time. (And
an instruction manual if you didn't get one with the canner.)

When you are satisfied that everything is present and working, run a test
with just water in the pan. Raise pressure to 5 psi and hold it for 15 or
20 minutes, watching carefully for leaks or drips that might indicate
problems. If there is a safety interlock to prevent opening while pressure
is present examine it to determine whether it has activated. Allow
pressure to drop and make sure the interlock doesn't release (not by trying
toopen the pan under pressure, but by visual examination) until pressure is
gone and you can remove the release weight without any steam escaping.


[ For deadweight canners the checks and tests are similar with the sole
exception of calibration which is never needed. Be sure you get the three
weights which create the 5,10 and 15 lb pressures when used
additively. --ED ]

Care Of Pressure Canning Equipment

To preserve low-acid foods which are safe, good tasting and nutritious, you
need to correctly use equipment which is well-maintained and in good operating
condition.

Safety Vents or Petcocks:

- Be sure the vent is clear and unobstructed. Use Q-tip or cotton
string to clean.
- Be sure vent tubes are screwed tightly into lid.
- If it is a model with vent under the handle, be sure the lever is
moving freely.
- If it is a model with a petcock, be sure it opens and closes
freely, either by screwing or flipping the lever up and down.
- If there is a film from hard water on the petcock, and it can be
unscrewed from the lid, soak the parts in vinegar, then wash and
dry.
- A ball and socket type petcock can be cleaned with silver polish.

Safety Overpressure Plugs:

- If it is a metal alloy or composition metal plug that screws into
the lid, do not try to remove it.
- If it is a rubber plug, use the thumbnail test to see if the
rubber is still pliable enough. If pressure with thumbnail leaves
a permanent dent in the rubber it is too brittle for safe use and
should be replaced.
- If either type of plug has been blown out by overpressure in the
canner, it must be replaced by a new plug. Do not try to reuse
the plug that blew out.

Gaskets:

- Soak gasket in hot water for an hour to soften before the first
use of the season.
- Insert gasket into its groove in lid. If it is either too
shrunken to fit to the edge, or too stretched to lie smoothly in
the lid, it must be replaced.
- Use thumbnail test - if pressure with thumbnail leaves a permanent
dent in rubber, it is too brittle and should be replaced. Rubber
safety plug should be replaced at the same time, since it will
probably be too brittle also.

Presto suggests coating the rubber gasket with vegetable oil before use. I
concur and further suggest a rubber gasket be given a little smear of oil
{ use a brush to avoid injury to the finger} when putting it on the pot. Dry
rubber can tear very easily due to friction against the metal. -ED]

On or about 4/1/2000, Bob, ( Zxcvbob) sent me email sugesting:

"Mineral oil or vaseline might be a better choice than vegetable oil for
lubricating a pressure cooker or canner seal. Especially after exposure
to heat, vegetable oils will start to "dry" and turn into a varnish.
First they get sticky, then eventually they harden like shellac. This
could cause the gasket to stick to the lid and the rim and tear when it
is separated, or crack later in storage." Thank you Bob.

I concur with this assesment. Testing shows vegetable oil does indeed bond
the rubber seal to the canner lid.

Henceforth the official position of this FAQ is that rubber gaskets on pressure
canners shall be lubricated with petroleum jelly (aka vaseline).



Pressure Gauge:

- Have dial and pop-up gauges tested every year before canning season
at your local Cooperative Extension Office. If it is inaccurate it
must be replaced.
- Check entrance port and carefully remove any debris that may have
accumulated.
- Be sure gauge is screwed firmly into lid. If it attaches with a
nut on the underside of the lid, be sure the nut is tight.

Weighted Pressure Regulators:

- Have no moving parts so there is no need to have them tested for
accuracy.
- Be sure they are clean, with no debris or food residue encrusted
especially in the sockets where the weight fits over its vent.
- Be sure the entrance port and vent pipe are open and unobstructed.
- Be sure there are no nicks or damage to the weight or to the tip
of the vent pipe where the weight fits.

[ especially the vent pipe which supports the weight. Damage here will affect
the proper action of the weight. Improper results may result. Note: a test run
which shows the 5lb weight rocks evenly when manually revolved around the vent
pipe shows a vent that is in good condition -ED]

Canner Lids:

- Be sure handles are securely attached.
- Be sure gasket fits smoothly into its groove in the lid.
- Set lid on canner and turn to lock it into place. It should turn
on smoothly and easily.
- If it does not turn on easily, check to be sure gasket is properly
seated in its groove. Adjust if necessary.
- If the gasket is properly seated, check the lid. If the lid is
warped or bent, it might be replaceable. Contact the manufacturer.
If it is an old model or no longer manufactured, there may be no
way to continue using it as a pressure canner. It may be used as
a regular pot for cooking. If this is the case, remove the gasket,
and if possible open or remove the gauge and overpressure plugs or
petcocks, to avoid the possibility of pressure buildup.
- If there is no visible problem but the lid continues to be tight, a
small amount of petroleum jelly or cooking oil may be applied to
the gasket to lubricate it.

Canner:

- Be sure there is a rack in the canner.
- Check the bottom for flatness. Older model canners may warp if
overheated. If the bottom is not flat or the canner will not sit
flat on the heating element or burner of the stove, it should not
be used for canning. Warped canners may be used for cooking.
Once warped, the damage *can not* be reversed.
- Put 1 inch of water in the canner, close the lid, heat the water
and pressurize the canner. Check to see if steam is escaping at
any point other than the petcock or safety vent.
- If steam is escaping around the gasket and it seems to be properly
in place, a *small* amount of petroleum jelly or cooking oil may
be rubbed around the gasket.

- With weighted gauge canners, if the weight only hisses continuously
and does not rock or jiggle intermittently as the manufacturers'
directions specify, check to see if the stove is level. This type
of weight must hang in a centered position on a vertical vent. If
the stove is not level the weight will not hang properly and steam
will escape in a continuous stream from the side, so the pressure
will not build up properly.

[ This will also happen if the pot is not properly exhausted before placing the
weights. The resulting condition is food that is not propely processed. A
similar end result happens when using dail gauges if the pot is not
exhausted. -- PFB via ED


- If steam is escaping around the base of any of the vents (dial
gauge, weight vent, safety vent, petcock) where they screw into
the lid, and if you can screw them out of the lid, the threads can
be wrapped with plumber's tape to seal them. Plumber's tape is a
stretchy, non-sticky silicon tape used to seal threads. It is
available in small rolls from a hardware store. Be sure to wrap
the tape in the right direction, so that when you screw the vent
back into the lid, the direction of the turning does not unwrap
the tape.

Canner Use

- Follow manufacturers' directions for use of your particular model.
- Use canner on the appropriately sized burner. A canner should not
hang over the edge of the burner by more than 2 inches on either
side.
- Be sure to center the canner on the burner. Some ranges do not
allow enough space to center a large canner on rear burners.

[N.B. Those newfangled smooth-top induction burners are a *poor* idea for
either a waterbath or pressure canner, both appliances are too heavy, and
the burner can't take it.--Diane Hamilton?

- Be sure lid is securely locked on (turned on, or screwed down).
- If your canner has six or eight large screws and wing nuts to
close it, screw them down in opposite pairs. If there are six,
screw numbers 1 and 4 down part way, then 2 and 5, then 3 and 6,
then return to the first pair to finish tightening continuing
around the lid.

VERY IMPORTANT for Pressure Canning: Exhaust the pot.

- For all models, be sure to vent the canner for 10 minutes on high
heat with a full stream of steam escaping. This is necessary to
remove air from the canner. Air remaining inside will lower the
maximum temperature achievable, and may cause underprocessing of
the food. After the 10 min. venting, close the petcock, or place
the safety weight or weighted pressure regulator on the vent.
Allow the pressure to build to 10 psig, or to 5 or 15 psig if you
are processing at those pressures. (psig means Pounds per Square
Inch by Gauge, the measure of pressure.) Be sure that you use the
proper time for the pressure level that you are using. Check the
new USDA Home Canning Guide for safe recommendations.


- When canner reaches the specified pressure, begin counting the
processing time.
- Reduce heat gradually to maintain the pressure without
over-pressurizing. With a weighted pressure regulator, leaving
the heat on too high will not increase the pressure, but will
cause excess steam loss from the canner, since steam will be escaping
continuously. Surpassing the specified pressure in a dial gauge
canner will result in soft, mushy or darkened food, and excessive
vitamin loss.
- If the pressure drops below its proper level during processing,
increase the heat to bring the pressure back up, then begin the
timing over again from zero, for the full specified time.
- Never run cold water over a canner to cool it. In addition,
excessively rapid cooling may cause jars in the canner to crack
or explode as the pressure in the canner drops more rapidly
than the pressure in the jars.

[ More commonly this produces a serious seepage problem as the jars with
high intermnal pressure are no longer restrained by an equal or greater
pressure in the pot. Seepage means a seal that is compromised - depending
on what is canned it can be a quite serious problem. Seepage means food is
present in the lid gum-to jar lips junction. Seal failure will occur
eventually and you know what that means --ED

- When the pressure has dropped to zero, wait another 1 minute before
opening the canner. On some models the pressure drop will be
visible when the overpressure plug drops back into the lid, the
rubber plug is no longer bulged, or the dial gauge will read zero.
Smaller canners will take at least 30 minutes to cool, larger ones
may take over an hour.
- Open the petcock or remove the safety weight carefully and wait
until any rush of steam has stopped. Then open the lid and tilt
the back edge up first, so that it directs the steam away from
your face. [and arms. Ouch!
- Remove the jars immediately. Do not leave jars sitting in a hot
canner overnight, spoilage may result.

Canner Storage:


- Turn the lid upside down and rest it on the canner. The weight of
the lid should not be resting on the gasket during storage as it
could deform it.
- For long-term storage at the end of the season, wash and dry the
canner well. Be sure all the parts (safety weight, rack, etc.)
are in the canner. A few crumpled newspapers in the canner will
absorb moisture and odors.
- If you unscrew the gauge or vents, coat the threads lightly with
petroleum jelly to prevent rust and make them easier to replace.
- Coat the gasket very lightly with petroleum jelly or oil.


Burpee, Health, National Victory and Dixie canners are no longer
manufactured, and no parts or service are available for these canners.
Parts and service are available for Presto, Mirro and All American, and for
some models of National Presto, Kwik Kook, Steamliner and Maid of Honor. If
you need further assistance or have other problems, contact your local
Cooperative Extension Office.

If you are thinking of buying a canner at a garage sale, check to be sure
you can open and close the petcocks. Look for stains or drips down the
sides or on the lid near the vents, they may indicate that the lid does not
seal or leaks steam all the time. Check that the lid twists on and off
easily. Check the condition of the gasket. Check that the base is flat.
A rounded base indicates that the canner is warped. Check that there is a rack.

Buying any of the models listed above as having parts and service available
is a much better bet than one of the older ones. [I.e. Presto, Mirro, and
All-American.


Prepared by Mary A. Keith, Foods and Nutrition, August, 1991
Revised by M. Susan Brewer, Foods and Nutrition, June, 1992
EHE-704

 

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previous page: 11.1.3 What do I need to know about gauges and weights?
  
page up: Food Preserving FAQ
  
next page: 11.1.5 Weight "jiggle" Questions