A little about me: I cook a lot, mostly dinner at home for my family and friends but sometimes for massive parties of upwards of 200 people. I’ve been doing sous vide cooking since 2010. I run a food blog called Unselling Convenience (also @unsellingconvenience on Instagram if you’d rather follow along there), which is mostly an inspiration board and memory database of things I’ve enjoyed cooking and probably want to cook again. I believe that shortcuts are great, but not at the expense of quality. I administer the Everyday Sous Vide and Instant Pot Love groups on Facebook. I’ve been writing about food for a few decades and have started collecting the good stuff at https://counter.kitchen. If you buy something from one of the links, I probably get a small commission which won’t even come close to defraying the amount of money I’ve spent on these things over the years but which will make me happy anyway.
Home canning (which is still called that even though it’s commonly done in jars, usually mason jars with two-part dome lids) is a practice of food preservation for room-temperature storage. I started home canning when I wanted to preserve the fresh summer bounty of pureed tomatoes for making sauce and I ran out of space in my freezer. But I usually do at least one batch of something else during the summer — most frequently tomato sauce of some kind and a jam or two. The pressure canner is also useful for preserving homemade stocks, especially things like beef stock where you might only use a little at a time and it needs to be stored for a while.
There are two primary kinds of home canning — boiling water canning and pressure canning.
When you’re canning, the primary pathogen you’re worried about is botulism. Most of the other common spoilage and pathogenic microbes are killed by boiling temperatures, but botulism is commonly found in soil and is particularly hardy.
Botulism normally requires the following conditions to grow:
- a range around room temperature
- a low-acid environment
- a low-oxygen environment
- a low-salt environment
- the presence of botulism bacteria or spores
You can inhibit growth of botulism by eliminating one or more of these conditions.
For canning foods, a few of these are non-negotiable — you want to store the food at room temperature, and the jars are airtight. Adding enough salt to inhibit microbial growth is going to make your food too salty to be edible (but see also fermentation).
That leaves acid and the presence of botulism itself.
For foods that are high in acid — great! you’ve eliminated the low-acid environment, so boiling water canning is sufficient. Pre-boiling the jars beforehand to sanitize them and then boiling for 5–10 more minutes to seal the jars is usually sufficient (though it can take a long time to heat the water to boiling). The boiling steps kill the other microbes, and the airtight environment keeps them from being contaminated after processing. Boiling temperatures are sufficient to kill botulism bacteria. They also form spores that can survive higher temperatures, but the high acid environment will prevent any that are present from reproducing and producing toxin.
For foods that are low in acid, you need to heat them to a sufficient temperature to actually kill the spores, and this is around 240F, well over the boiling temperature at normal pressure. In a pressure canner, water and steam can reach the temperatures necessary, but unlike with boiling water canning, the entire contents of the jar must be heated through to that higher temperature for a sufficient amount of time. This is why pressure canning recipes almost always specify longer processing times, sometimes more than an hour.
That said, botulism toxin is inactivated at boiling temperatures, so you should always re-boil pressure canned foods for 10 minutes before consuming them, as an extra precaution.
As with my other guides, I have no specific food safety credentials and you should not listen to random people on the internet. This is my attempt to explain the issues in an understandable way, but you should not consider me an authority if you’re unsure about any of this.
I strongly recommend the Ball Complete Book of Home Preserving for canning specifics and many recipes.
The overall process is fairly simple. The following are general steps for your information — always follow a specific tested recipe!
For boiling water canning:
- Clean and sterilize your jars by boiling them fully covered for 10 minutes. Some dishwashers may have a sterilization mode, and that will work too. Prepare the flat lids and wash enough bands.
- Cook the food you’re going to can
- Heat the flat lids in a separate pot in water, until just below boiling, and leave the in warm water. This softens the seals.
- Using a jar lifter, remove one jar at a time, empty the water out, put the jar on a clean dish towel, and using a canning funnel, fill the jar with the hot food up to close to the top, leaving a small amount of head space. Wipe the jar rim, place a flat lid on top, and screw a band on fingertip tight. If it’s overly loose, the lid won’t make a good seal — the lid should be slightly pressed against the rim. But if it’s too tight, the air in the headspace won’t be able to escape and either the lid won’t seal properly or the jar may crack.
- Put the jar back in the canner with the jar lifter, and repeat until all of the jars are filled or you run out of food. Don’t leave empty jars in the canner.
- Cover the jars with 2–3 inches of water, and bring to a full rolling boil. Boil for 10 minutes or according to your recipe’s instructions.
- Turn off the heat, and let the water cool for 10 minutes. Remove the jars without tilting them and put them on top of a clean dish towel (I usually put that on top of a cutting board or sheet pan for easy moving), and drape another clean dish towel over the top. Leave for 24 hours. You may hear a “ping” sound as the jars cool and the vacuum seal engages, but the lack of a ping doesn’t meant the jars didn’t seal.
- Press down on the top of each lid and make sure there’s no give. Remove the band and lift the jar from the lid. If it stays attached, the seal is good. Clean the outside of the jar with a paper towel soaked in white vinegar, and let dry. Label the lids with the contents and the date. Store them without the bands, which can trap moisture.
- Any jars that did not seal must be either immediately reprocessed or refrigerated and consumed within a reasonable time frame. Reprocessing can lower the quality, so I’d probably eat them. But in over a decade of home canning, I’ve never had a lid fail to seal.
For pressure canning, the process is mostly the same with a few minor changes:
- The jars do not need to be sterilized first, the pressure canning process itself will do that. They should still be clean.
- Only 2–3 inches of water at the bottom of the canner is needed, not enough to cover the jars. The jars should still start in cold water and be heated with the water.
- After all of the jars are added back to the canner, seal the lid and bring the water to a boil so steam escapes from the vent for 10 minutes, then put on the pressure regulator. When the pressure reaches the desired level (usually 10 pounds unless you live at high elevation), start timing.
- When done, turn off the heat and wait until the pressure returns to zero. Remove the pressure regulator and wait two more minutes. Open the lid (away from you, a lot of steam will escape), and wait ten more minutes. Then remove the jars to a clean towel and cover them as usual.
- As a precaution, after opening a jar, boil the contents for 10 minutes before eating. It’s unlikely, but if any botulism toxin has been produced, this will deactivate it.
- Home-canned food is best consumed within 1–2 years. It is generally safe as long as the seal is still good, but the quality may deteriorate over time.
- If the lid seal is broken, or the food shows any sign of spoilage, discard it. For pressure canned foods that have spoiled, it must be detoxified before discarding. See the instructions in the Ball Book or similar if this is a concern.
- Jars that are chipped may crack — inspect them carefully before using. Jars are also subject to cracking with thermal shock (temperature lowering or raising too quickly). Always allow the proper time for jars to heat up and cool, only put hot food into hot jars, and don’t put them on surfaces that may transfer heat too quickly (directly on the bottom of the pan, or on a metal or stone surface). If a jar cracks in the canner, abort the process — empty out all of the filled jars, let everything cool, clean up the mess, and start again.
Mason Jars are super useful! I cook a lot of things in them, use them for storage, canning, fermenting, and sometimes sous vide. They are sometimes difficult to find, buy the ones you like when you see them. My favorite sizes are wide mouth pint, wide mouth quart, and 4 oz. jelly jars.
Mason Jar Lids
Most of the pieces of equipment involved are reusable, with the exception of the dome part of the lid. You can wash and reuse these for non-canning storage if you like, but for can sealing, you should always use fresh brand-new ones. They come in regular mouth and wide mouth.
It’s an investment, but if you’re going to do a lot of this, the All American Pressure Canner is completely worth it. It has no seals to wear out, and should give many years of service (I’ve had mine for 8 years, and it shows a little spotting on the aluminum but otherwise no signs of wear). If you’re just doing boiling water canning, any large stockpot will do in a pinch, or an actual canning pot will have some convenience features. Not optional: a rack so the jars don’t sit directly on the bottom of the pot.
A note about the Instant Pot: most models are pressure cookers, but are not rated to reach sufficient and constant enough pressure for pressure canning, except the Instant Pot Max, which no longer seems to be in the lineup anyway. The Instant Pot can be used for boiling water canning, but I generally don’t recommend it because the capacity is so small. Most of the effort is in preparing the food and the actual canning process, and doing a few more jars at the same time is relatively little incremental effort, so my advice is if you’re going to do this project, go as big as you can. If it’s more than you’ll eat yourself, they make great gifts (especially jams).
It’s possible to pop the seal on a canned jar with a spoon, but it can be difficult. A jar popper makes this very easy.
That’s about it!