If you want to know how to preserve food by pressure canning, this article is what you need. You may want to check out my boiling water bath article as well.
First, what foods must you pressure can? Low-acid foods. In this context, low acid is defined as “pH 4.7 or higher”. Vegetables, meat, fish, stocks, and finished foods like stews or soups all need to be pressure canned. Tomatoes are a special case as they are right on the cusp of pH 4.6, so they can be canned using either the boiling water bath method (with added acid like lemon juice or citric acid) or by using pressure.
Second, what is a pressure canner? Can I just use my pressure cooker?
The simple answer is “no”. Most domestic pressure cookers are not rated or constructed to take the sustained pressures for which a pressure canner is designed. When processing beans with my easy prepare method, for example, I am canning at 10psi for 90 minutes. Unless your pressure cooker specifically states it is rated for pressure canning, it is not suited to this task. Canners like the Presto 23qt canner I have (see picture) cost around $80 and are a worthwhile investment – you can use it as a pressure cooker, pressure canner, AND as a boiling water bath canner.
A note on pressure canner gauges. If you intend using the pressure gauge, you must get the gauge checked for accuracy every year. This is a free service by most county extension services in the USA. I use a jiggle weight because I can always tell when the canner is at the right pressure – I listen for the “pshht pshht” noise of the jiggle.
Third, you need lids and bands. New jars come with lids and bands, but you should pick up extra lids when you can get them at a good price. The bands are reusable for many canning sessions – they only need to be discarded if they show signs of rust or corrosion.
And finally, you need something to put in the jars – the “jar contents”.
To start a pressure canning session, first clean the jars you are going to use. Running them through the dishwasher works well; if you don’t have a dishwasher you can wash them in the sink. Once they have been cleaned, put them in the canner, fill the canner with hot tap water to the appropriate fill line marked on the inside of the canner (see your canner’s instruction sheet) and put a little hot tap water into the jars to keep them from falling over. Once the jars are resting in the hot tap water, put the lid on the canner to retain heat, put the canner on the hob, and set it to a medium-low temperature.
This is all before you do anything to the “jar contents”. You are aiming to have the jars at a good hot temperature before filling them with the “jar contents” – too much of a temperature difference between the jar and the contents leads to thermal shock, also known as “glass shrapnel and incendiary contents spread across the kitchen”. Thermal shock is generally considered A Bad Thing(TM) and is definitely to be avoided.
Once the “jar contents” are starting to cook, increase the heat under the canner with the aim of getting it to a boil once the “jar contents” are ready. It’ll take you a little practice to know exactly when to turn the heat up, but don’t sweat it too much – you can keep the “jar contents” nicely hot for a few extra minutes if needed, and it doesn’t really matter if the empty jars are heating for longer than needed.
Give the lids a good clean with plenty of soap and hot tap water and then rinse thoroughly. I have seen many people saying to boil the lids and then keep them in the hot water straight after boiling, but according to the Ball Complete Book of Home Preserving (which I cannot recommend strongly enough – it is absolutely essential for a home canner), all that is needed is to keep them to a simmer – 180F/82C.
Once your lids and jars are ready, you can ladle in your jar contents (the soup, stock, stew, beans, etc.) and then seal the jars.
SEALING THE JARS
Once each jar is filled to the appropriate level (usually within 1/2 to 1 inch of the top of the jar depending on the recipe) you should wipe off the rim of the jar to make sure that there is nothing on the rim to interfere with a proper seal. Use a paper towel sprayed with a 50/50 mix of white vinegar and water to wipe off the rim. Lift lids out one by one and place on the rim. Screw down the bands to “finger tight”: use your fingertips to screw the lid down until you can’t tighten it any more, but do not tighten the lid as tight as you possibly can. The purpose of this step is to secure the lid on, not to seal it completely – there needs to be a little looseness in the band to allow air to escape, but equally you don’t want water to get into the jar. The jar seal comes from the vacuum you will create in the water bath stage.
PUTTING ON THE SQUEEZE
Once your jars, lids, and “jar contents” are ready, it’s time to put them into the canner on the rack at the bottom.
Place the lid on the canner, bring the canner to a full boil, and vent the canner for 10 minutes. Count the 10 minutes from when the stream of steam is running full blast – on my canner I get a whistling noise at this point. You can tell that the appropriate point is reached when the steam is a solid column – this is when you start your timer.
Once the 10 minute vent is completed, put the weight on the vent and process for the amount of time specified in the recipe. Once the processing time is up, take the pot off the heat and walk away. You need to let the pressure canner return to normal pressure. This will take a variable amount of time, but you cannot hurry this step – remember thermal shock! Once the pressure gauge has dropped to normal, leave the canner for an additional 10 minutes then take the lid off the canner. Use your jar lifter or tongs to take the jars out of the hot water to cool.
COOLING THE JARS WITHOUT THERMAL SHOCK
The best way I have found to cool jars without having any danger of thermal shock (hot jars and cool countertops do not mix) is to use a cookie rack. This allows free air circulation around the jars without putting them onto any surface which could turn them into bombs.
Leave the jars overnight; the next day you can take the screw bands off and test the seal.
TESTING THE SEAL
Testing the seal is easy. If you can lift the jar up by the lid, the seal is good. If you can’t, the seal is bad! If a jar didn’t seal properly, treat it as an eating jar and just finish the contents within a few days or freeze the jar and its contents for later use.
RULE OF THUMB
The rule of thumb when calculating how long to pressure can for: look up each ingredient on the USDA list separately. Note the longest time any single ingredient requires. Pressure can for that amount of time – the longest amount of time required by any single ingredient.
You were waiting for me to say what the jar contents are? Well… that’s up to you. Go for it!