The Best Canning Pressure Cooker – A Quick Introduction
Preserving food by canning, whether using the water bath method or by canning under pressure, is an excellent way to save money while ensuring that your family is eating produce that you have selected – or grown – yourself.
Canning allows you to buy fresh produce when it is in season, and is therefore less expensive, and then preserve it for use later in the year when the only fruits and vegetables available are shipped from places unknown and are costly. Of course, it’s great if you grow your own fruits and vegetables, but otherwise, when something is in season, it is usually easy to find good deals that will make home canning worthwhile.
The best way to can foods is through the pressure canning method. Pressure canners are specifically designed for this purpose and have been tested and retested to ensure that they work properly.
How does a pressure canner work ?
Pressure canners (and cookers) work using a basic principle of physics. At sea level, in a normal pot, water can only heat up to 100 degrees Centigrade (212 F). No matter how much flame is under the pot or how much or how long it is heated, it will always stay at that temperature. Instead, sealing the liquid under pressure – that is, locked inside the pot so that it cannot escape as steam – traps the vapour that rises from the liquid.
As the pressure rises, the temperature of the water and steam inside the sealed pot (the pressure canner) also rises above the normal boiling point temperature. For example, when the pressure selector on a modern pressure canner is turned to 15 pounds per square inch (psi), i.e. usually the highest setting, the temperature increases to 121ºC.
This means that food cooks more quickly, but also means that the higher heat will kill bacteria much more effectively than the traditional water bath method.
A pressure canner uses a particular method of heat processing. Glass jars are filled with the produce to be preserved along with some liquid, either added to the fruit or vegetables or as an integral part of it. The filled jars are closed using metal lids and screw bands and the jars are placed in the pressure canner filled with water. As the jars are heated the internal pressure changes as air is expelled from the jars.
When the process is completed, the atmospheric pressure outside the jar is greater than the pressure inside. As the jars cool, a vacuum seal is formed. This vacuum seal prevents air from getting back into the produce, which would of course bring with it micro-organisms such as mold, yeast, bacteria and enzymes that would spoil the food and contaminate it.
Pressure canning is the only safe method of preserving vegetables, meats, poultry and seafood. Only in a pressure canner can the temperature reach at least 240° F. Food in the canner is processed for the required amount of time depending upon the type of food and the altitude.
While most bacterial cells are killed at the normal boiling point of water, they can form spores that can withstand these temperatures. The spores grow well in low acid foods, in the absence of air. When the spores begin to grow, they produce the deadly Clostridium botulinum toxin.
Foods that are low acid have a pH of more than 4.6 and because of the danger of botulism, they must be prepared in a pressure canner. Low acidic foods include: meats, seafood, poultry, dairy products, and all vegetables.
High acid foods that have a pH of 4.6 or less contain enough acid so that the Clostridium botulinum spores cannot grow. High acidic foods, i.e. fruits and properly pickled vegetables, can be safely canned using the boiling water bath method. Certain foods like tomatoes and figs, that have a pH value close to 4.6, need to have acid (lemon juice or citric acid) added to them in order to use the water bath method. However, all foods can be easily and safely canned using a pressure canner.
Pressure canning basics
There are basic differences between a “pressure cooker” and a “pressure canner”. In short, a pressure canner can also be used as a pressure cooker, but it is not a good idea to use a pressure cooker for canning. Pressure canners are designed specifically to accommodate the pint and quart jars that are used for canning. A smaller pressure cooker, while great for making a pot roast for example, is not made for the high pressure cooking that is required for canning. Pressure cookers designed for canning allow for stable processing in terms of time, temperature, and the correct pressures to meet safe food preservation standards.
The first thing to consider when buying a pressure cooker is the material. Pressure canners are available in stainless steel and aluminum. Stainless steel looks more attractive and is strong and resilient but does not conduct heat as well as aluminum. In fact, a good stainless steel pressure canner will have an aluminum or copper base to guarantee even heating.
A heavy cast aluminum pressure canner can be an excellent choice because it conducts heat well and is lighter than stainless steel. Many pressure canners are not suitable for glass or flat top ranges, so be sure to check this aspect before buying or using a pressure canner.
An important element in pressure cookers is the type of seal employed. A number of pressure canners use a rubber gasket, while others have a metal to metal seal. In this case, the lid attaches securely to the base using screws or clamping locks that align the lid to the base. Both are efficient, form a steam-tight seal and meet safety standards.
Having a metal to metal seal means that you will not need to worry about when to replace a worn, stretched or hardened rubber gasket. The gasket needs to be carefully monitored, because if it is not tight leakage can occur making it difficult to reach the right temperature and can even cause the canner to boil dry.
Pressure canners come in varying sizes, and your choice will depend upon the volume of canning you plan to do each time you use the canner. The smaller size usually holds 7 pint jars or 4 quart jars, and the largest size would hold likely hold about 32 pint jars or 19 quart jars, with interim sizes giving a wide choice for various needs.
All pressure canners have a geared steam gauge with an automatic overpressure release (this is obviously very important). There are usually three pressure settings available: 5 psi, 10 psi and 15 psi. The “psi” stands for “pounds per square inch or “pound force per square inch”. When choosing a pressure canner you should check that the pressure gauge is easy to read.
The pressure canning process
Step One: Prepare equipment and preheat the canner
Assemble and wash equipment and containers (before preparing the produce).
Fill the boiling water bath or pressure canner with the appropriate amount of hot water and begin heating it on the range. For a pressure canner this will usually be 2 to 3 inches of water in the bottom of the canner (but be sure to read manufacturer’s instructions carefully).
Since this can be difficult to determine before jars are placed in the canner, it is useful to have an extra pan of water heating in case you have too little water in the canner. If you heat too much, be prepared to remove some.
Examine jars and discard any that have nicks, cracks, or rough edges. These defects will prevent an airtight seal, and food could spoil. Discard rusted or bent ring bands. Wash canning jars in soapy water, rinse well, and keep hot. This can be done by using a dishwasher or by placing the jars in the water that is heating in the canner. The jars need to be kept hot to prevent breakage when they are filled with a hot product and placed in the canner for processing.
You must sterilize jars that will be filled with food and processed for less than 10 minutes in a boiling water bath canner. This can be done by boiling them for 10 minutes (for 1,000 feet altitude). Add one additional minute for each additional 1,000 feet of altitude.
Jars that will be processed in a pressure canner will be sterilized during processing. Always use new two-piece lids. Follow the manufacturer’s instructions for treating them. Keep jars, lids and rings in very hot water until time to use.
Step Two: Prepare the food to be preserved
Wash the product carefully, a little at a time. Lift food out of the water, drain the water, and continue rinsing until the water is clear and free of dirt. Dirt contains some of the hardest-to-kill bacteria. Don’t let the food soak; it will lose flavor and nutrients. The raw food should be as clean as possible to make the canning process as effective as possible.
Pack the food according to directions. Fruits and vegetables may be packed raw or preheated and then packed. Some foods can be packed by either method, but always follow the directions given in the recipe. Hot pack often gives better color and flavor, particularly when foods are processed in a boiling water bath.
A jar funnel is helpful when you fill jars with small foods. There should always be enough liquid to fill in around the solid food in the jar and to cover the food – usually ½ to 1 ½ cups liquid for a quart jar.
Leave the specified amount of headspace in the jar. The amount depends on the type of food, so follow the directions in the recipe. Close the jars correctly. To release any air bubbles that may be trapped in the jar, run a bubble-freer or any plastic knife-like utensil around the edges of the jar, gently pushing the food from side to side so that any trapped air is released. Add more liquid, if needed, to ensure proper headspace.
Wipe off the rims of the jars with a clean, damp cloth. Place the treated lid on the jar, center it, and hold it in place with your fingers while you tighten the screw band to fingertip tight. Tightening the screw band too tight will prevent air from escaping as necessary during processing.
Step Three: Canning method
Choose the correct canning method. Use boiling water bath for fruits or high-acid foods. Use pressure canners for all other foods. For pressure canning, read the canner manufacturer’s instructions and follow them carefully. Be sure to vent or exhaust all pressure canners for 10 minutes before closing them up to pressurize. Basic pressure canner procedure is as follows:
1. Center canner over the burner. When the jars of food are ready for canning, put the rack and 2 to 3 inches of hot water into the canner. Begin heating the water, but not enough for the depth to decrease.
2. Use a jar-lifter to place filled jars, fitted with lids, on the jar rack in the canner. Leave space between the jars for steam to flow around each one during processing. Keep the jar upright at all times.
3. Fasten the canner lid securely. Leave the weight off the vent port 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 port or petcock. Let the steam flow continuously for 10 minutes (to vent the canner).
5. After venting the canner, place the counterweight or weighted gauge on the vent port or close the petcock, depending on the type of canner. If you have a weighted gauge, be sure to use the correct setting. The canner will begin to pressurize.
6. For a dial gauge canner, let the pressure rise quickly to 8 pounds of pressure. Lower the burner temperature slightly and let the pressure continue to rise to the correct setting.
7. For weighted gauge canners, let the canner heat quickly until steam begins to escape from the gauge or the gauge moves and makes noise. Adjust the heat down slightly until the weighted gauge begins to jiggle or rock as the manufacturer describes.
8. Start timing the process when the pressure reading on the dial gauge indicates that the recommended pressure has been reached or when the weighted gauge begins to jiggle or rock as described.
9. Adjust the heat under the canner to maintain a steady pressure at, or slightly above, the correct gauge pressure. If the pressure goes too high, do not lower it by opening the vent or lifting the weight. Instead, turn down the heat under the canner.
10. If at any time the pressure goes below the recommended amount, bring the canner back to pressure and begin timing the process again, from the beginning (using the total original process time).
11. When the time process is complete, turn off the heat, remove the canner from an electric burner if possible, and let the canner cool down naturally. If the canner is too heavy, simply turn off the heat.
12. Do not force-cool the canner or depressurize it. It will depressurize while it is cooling.
13. After the canner is depressurized, remove the weight from the vent port or open the petcock. After 10 minutes, unfasten the lid and remove it carefully. Lift the lid with the underside away from you so that the steam does not burn your face.
14. Do not leave the canner unopened to cool completely.
15. Using a jar-lifter, remove the jars, being careful not to tilt them. Do not turn jar upside down to test for leaks because liquid could seep between the lid and jar top, breaking the seal. Carefully place the hot jars directly onto dry towels or a cooling rack. Leave at least 1 inch of space between jars.
16. Let the jars sit undisturbed while they cool for 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 cool.
After 12 to 24 hours, make sure the jars are sealed. Most lids will seal with a pop sound while they are cooling. When it is completely cool, test the lid. It should be curved downward and should not move when pressed with a finger. If a jar is not sealed, refrigerate the food and use it within two or three days. You may also reprocess the food within 24 hours or freeze it.
Label each jar and store in a cool, dry place.
It is important to use recipes from reliable sources because these recipes have been tested for safety and quality.
first image: mellowynk cc
second image: NathanaelBC
third image: UGA College of Ag & Environmental Sciences – OCCS
forth image: podchef