Family, Consumer Sciences, Nutrition

• PRESSURE CANNERS USE , TYPES AND CARE

  In canning fish, meats and vegetables (except tomatoes) it takes higher than boiling temperatures to make sure of killing bacteria spores that cause dangerous spoilage. The only way to obtain these temperatures is to use equipment that keeps steam confined until it builds up pressure that will allow a temperature of 240° to be reached. To use pressure equipment successfully and safely a person must understand how it operates and follow directions carefully.

  If manufacturer directions for use are not available, follow these steps:

  A. ALTITUDE ADJUSTMENT - Determine the proper poundage for the altitude at which the canner will be used.

  Adjustments needed for dial-gauge pressure canners: Above 2,000 feet add 1/2 lb. for every 1,000 feet above sea level.

Adjustment needed for 5-10-15 lb. weight gauge - above 2,000 ft., use 15 lb. weight.

Adjustment for constant weight gauge, 12 qt. or larger canner, see manufacturers time chart. 4-6 quart cooker canner - do not use over 3,000 ft. above sea level.

B. PETCOCK - Determine where the petcock (vent stem) is. These vary depending on age and type of canner (see section on TYPES). Learn how it operates (see VENT section).

 C. Test The Gauge - A dial gauge should be tested at the beginning of each season. If you have not operated the canner, have the gauge tested before using. (If a canner has been cleaned and stored properly, (see CARE) and not moved during storage, gauge need only be checked every two years.) Always test a gauge if the canner has been transported, jostled, dropped or treated in any way that might cause a change in the precision calibration of the dial gauge.

Contact local Extension office for information on this service. (See Service in Action X9.716, "TESTING PRESSURE CANNER GAUGES USING A MAXIMUM TEMPERATURE THERMOMETER".)

If the test shows that the gauge does not register accurately, make a permanent tag to attach to the canner. Record the amount and direction of the error so that any person operating the canner will know how to obtain the pressure needed. For instance, a gauge may read 11 pounds when the pressure inside is actually 10 pounds. A needle that moves sporadically or that registers more than 5 pounds high or low should be replaced (see GAUGE section).

OPERATION : If you have not used the canner before follow OPERATION STEPS carefully, omitting steps 3 and 12.

Watch for steam leaks . (Escape of a little steam from under a weight gauge is normal). No steam should be expelled. If steam escapes around the cover, examine the sealing edges of the bottom and lid. If they are not smooth, clean with a fine cleaning powder, rinse well and dry.

Check the gasket -it should be pliable and fit completely into the groove all the way around the lid. If a gasket is reversible, turn it over and replace it in the groove as it may improve the seal.

Leakage makes it more difficult to maintain a constant pressure. It may cause a canner to boil dry and/or liquid may be drawn from the jars.

OPERATION STEPS:

1) Make sure a rack is in bottom of the canner.

2) Place 3" of water in bottom of canner.

3) Place filled jars on rack so steam can flow around jars without jars touching each other. If two layers of jars are desired, place rack over first row and stagger the second layer.

4) Secure lid properly (see "TYPE'' section) so that no steam can escape. If gasket type, make sure it's in good condition. (Not all canners have rings -- see "GASKET" section).

5) Turn heat to high and leave petcock (vent) open 10 minutes. This allows the steam that is forming at the water level to push out air so that the steam fills the entire canner. This ensures that a proper pressure will be obtained.

6) After venting (watch for a full stream of steam being expelled from the vent) close the petcock. Watch the dial gauge' as the pressure begins to build immediately. For a weight gauge, be attentive to when its rocking begins.

7) Build up and hold pressure :

For dial gauge - when needle is 1/2 lb. below desired poundage drop heat back (pressure will continue to build momentarily). Start processing time when full pressure is reached. Regulate heat to keep at desired temperature Pressure may vary slightly. DO NOT LOWER PRESSURE by opening petcock.

For a weighted gauge - Watch for weight to rock slightly (this means it's up to desired pressure). Start counting processing time at this point. Reduce heat to keep weight gently rocking two or three times a minute, only. Spewing causes liquid to be pulled out of the jars.

8) When processing time is completed , remove canner from stove. Place on separated bricks or boards at floor level to allow air to circulate under and around canner (do not place in draft).

9) Let canner cool until dial gauge registers zero pressure or when weight gauge does not spew when touched. DO NOT HURRY COOLING BY USING COLD WATER.

10) Open pet cock or remove weight slowly (a small amount of pressure is still in canner).

11) Open lid carefully and slowly lift it off away from the body. (If canner sets too long after pressure has gone down, a reverse vacuum can form, making it very difficult to remove.

12) Remove jars and place on towel on a table or counter with ample space to allow air to circulate around all jars (at least 1" apart). Avoid a drafty area. NOTE: Jars left in a cooling canner for more than 1 hour can develop a flat, sour spoilage.

13) Let jars stand until cool . A seal will form if not already sealed. DO NOT TURN JARS UPSIDE DOWN

TYPES OF CANNERS :

A wide variety of Pressure Canners are safe to use for canning low acid foods at home --- vegetables, fish, meat, mushrooms and many combinations of these foods.

I. Typical dial gauge pressure canner:

The appearance of dial gauge canners may vary considerably because of the way in which the lid is sealed onto the bottom -- twist on, thumb screws, clamp band, or flex lid. However, all styles will have similar dials, vents and safety valves on the lid (see essential parts section).

Some styles require gaskets. Those that do have a lid that twists onto the bottom to seal. (Fig. A)

Some styles do not require a gasket. Those that do not, have a lid that in some way fits into the bottom and is then sealed. Both operate efficiently when directions are followed carefully. (Fig. B)

	Dial gauge with petcock and safety valve combination

Altitude adjustment for dial gauge canners is covered under "USE"

The basic unit generally appears very similar in style and the way in which it seals, however, there are at least 3 types of weight gauges:

III. Typical constant weight gauge (15 lbs.) canners, generally, are similar in shape with a twist on seal type lid very much like the 3-weight gauge pressure canner. However, the constant weight gauges may appear different in shape.

Fig. D

On this type canner, the safety plug can be a black rubber disk or an aluminum plug.

IV. Pressure Cooker Canner Sauce Pans - 4-6 qt. size

PRESSURE REGULATOR - gauge which indicates and regulates the steam pressure. Fifteen pounds pressure is ideal for cooking foods.

VENT PIPE - projecting tube on the cover which holds the pressure regulator and allows steam to escape.

AUTOMATIC AIR VENT - exhausts air from the pressure cooker before pressure is built up. Also acts as an emergency release if pressure builds up beyond safe levels.

COVER - special lid which seals the pressure cooker by -compressing a gasket between the interlocking lugs of the cover and the body.

SEALING RING - gasket made of a rubber-like material which fits into the cover and forms a pressure-tight seal for cooking.

BODY - special saucepan with lugs which inter-lock with the cover lugs.

COOKING RACK - a perforated rack placed into the pressure cooker body for cooking foods out of water.

ESSENTIAL PARTS

.Dial Gauges : A gauge, whether dial or weight is essential to control pressure and lets the operator know how much pressure is built up inside the canner. This pressure level is controlled by the heat source.

Dial gauges are visual and can be held at selected poundage for various altitude adjustments (see altitude adjustment under "USE" ).

These gauges should be tested seasonally and after any mishap or major move. (See Test the Gauge, "USE" section). If test shows that gauge reads inconsistent or is off 5 lbs. or more, it should be replaced.

.Weight Gauges: Give an audible sound - 2 or 3 wiggles a minute -- when the 10 or 15 lb. pressure has been reached. The weigh moves (rocks, jiggles or wiggles) to release excess pressure but the heat source must be controlled so the weight does not continually release steam by spewing. When pressure is released too frequently or constantly, liquid is pulled from the jars inside. THIS IS A COMMON RESULT IN JARS CANNED IN A WEIGHT GAUGE CANNER. If the jars stay sealed after they are cooled the product inside is safe to use even though the liquid is down. Pulled liquid may keep some jars from sealing.

(This type of gauge also serves as a safety value)

At altitudes between 2,000 and 10,000 ft. above sea level, the 15 lb. weight must be used for safety which results in cooking products at a higher temperature (see chart). This affects the texture of the finished products so following standard time charts carefully is important. DO NOT CUT BACK ON TIME BECAUSE PRESSURE IS HIGHER. NO SAFE GUIDELINES HAVE BEEN DEVELOPED FOR. SUCH ADJUSTMENTS.

Table 2: Temperature, pressure, altitude chart

.Gaskets : Gaskets of rubber or rubber like compound keep steam from leaking out around cover. Most gaskets are removable for replacement as needed. Some can be turned after a period of use to insure a tighter seal.

A gasket must be replaced when 1) it no longer fits snuggly and completely in its groove: 2) it is too stiff to return to its original shape when pulled. Replacement gaskets are available from hardware stores, appliance repair shops or from Presto and Mirro manufacturers

To help gaskets twist on and off without distortion, use 1 drop of salad oil on the finger and move it around the surface of the gasket. DO NOT USE MORE OR SEAL WILL NOT BE TIGHT.

Some canners do not require a gasket. These seal "metal to metal" and are. as effective as those with a gasket (see TYPES OF CANNERS, I).

.Safety plugs or Valves : All canners have a safety plug or valve in addition to the vent petcock system. Safety plugs go into action only if pressure or temperature becomes dangerously high.

*Metal alloy plugs (round metal plug in lid) melt when pressure gets too high or utensil boils dry.

*Composition-type plugs (black rubber like plug in lid) are blown out by excessive pressure. Both types are replaceable.

*Ball and socket safety valve: The stem and ball or needle lifts under excessive pressure to release steam.

Other safety devices are weights that rock or jiggle and blow off when excessive pressure is built up. (Safety weights will rock vigorously at 20 lbs. pressure).

.Vents : Each type canner has a vent stem to allow air to be exhausted from the utensils and to permit the release of steam if needed. A petcock, safety valve' or weight on the vent is used to control the escape of air or steam.

*Canners with dial gauges may have one of the types shown below, or a weight which is lifted by excess steam. (Fig. H.)

*Canners with a constant weight gauge have been designed so that the gauge controls both the pressure and the release of steam. (Fig. E)

CAUTION : Allowing too much steam to escape through a vent stem topped with a weight gauge will cause liquid to be drawn out of the jars. These canners must be watched just as carefully as dial gauge canners to control the pressure and keep it as steady as possible. This control is achieved by raising or lowering the heat source (every range operates a little differently).

*Another Needle Type is a simple thumbscrew that is opened when untwisted (counter clockwise) and closed when twisted thumb tight (clockwise), not overly tight.

CARE

Pressure canners are made from materials strong enough to withstand pressure. However, proper care will add to the canner's life expectancy of 20 years or more.

Aluminum -- cast or heavy-gage sheet -- is the most common. In hard water areas the inside will darken and should not be scored to metal shine. Also, some hard water has a high content of salts which cause aluminum to pit more readily. Thorough cleaning and drying will help eliminate pitting.

Stainless steel is sometimes used for canners and in lids for some enameled steel canners. Water does not effect stainless steel but such canners are generally more costly.

Some early dated canners are made of enamelware or tinned steel, both of which should be handled with care to avoid damage. Damage during storage is common so inspect carefully if buying a used one of this typed

Wash and dry canner bottom thoroughly after each use. Leaving damp, to air dry, tends to increase pitting of aluminum.

Do not put a dial gauge lid in water to wash. This will easily damage the dial. Wipe the inside of the lid with a soapy cloth and then wipe with a clean damp cloth and dry thoroughly.

Before storing canner, remove petcock or weight and other safety plugs when possible to clean. Draw a string or pipe cleaner through all openings. Wash and thoroughly dry all removable parts before replacing them. Remove petcock and safety valve. If they are crusted or gummy soak in vinegar, then wash and dry. Clean the ball and socket with a silver polish. Put all parts back together carefully and correctly.

It is not necessary to remove the gauges for testing, cleaning or storage. However, if it is removed, replace it carefully as the threads are fine and can easily be cross threaded.

Store a canner carefully. Make sure it is clean and dry. Coat threads of thumbscrews and/or wing screws with a very thin coat of vegetable oil (salt free) or petroleum jelly. In moist climates, put crumpled newspapers inside the canner to absorb moisture and odors. Wrap lid in several layers of paper and invert over bottom DO NOT INVERT LID UNWRAPPED AS MOISTURE AND DUST CAN ENTER DIAL AND CAUSE CORROSION INSIDE DIAL.

CHECKLIST FOR BUYING A USED PRESSURE CANNER

Is the gauge attached or with canner? (Weight and dial can be replaced)

Is petcock safety valve complete? (Replacement parts are available)

Are threads of opening undamaged? (Opening cannot be rethreaded)

Does seal require a gasket? (Most sizes are available)

Is metal to metal seal smooth around lid and bottom with the minute manufactured grooves visible?

Is the canner in "round"? When looking directly into the canner, does it appear to be exactly round and not oblong or bulged in one place?

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.

Many early dated canners are useable but may need replacement parts and a good cleaning.

Replacement parts are available at a variety of hardware stores, as well as from appliance repair shops and manufacturers of today's canners. Such parts may not look exactly like 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.

To simplify technical terminology, trade names of products and equipment occasionally will be used. No endorsement of products named is intended nor is criticism implied of products not mentioned.

Special Thanks to Daryl McGuire, 2000 Master Food Preserver and the Tri River Area Website for compiling this information!

The Colorado State University Extension Office for San Miguel and West Montrose County in Norwood can check your canner gauge. Call for an appointment at 327-4393.

Page Updated: August 14, 2006
Webmaster: Mary Watson

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