Casaubon's Book

Pressure Canning 101

Note: This is part of a two-part piece on the basics of canning (the whole thing in more refined form is contained in _Independence Days_ as well). In a previous post, I wrote about putting canning in perspective – it is not all of food preservation, nor is it essential. That said, however, I get more questions how how to can than all other forms of food preservation put together, so since my food storage class is doing Pressure Canning this week, I thought I’d re-run essays I’ve written about how to can. I should note, I ask that anyone who has never canned before (or not for decades – they changed the rules in 1994, so you may not be remembering correctly) should begin with water bath canning. So why am I putting up the Pressure Canning post first? Well, because I want the water bath canning post to be at the top of the screen when you come to the page. So if you are getting this on RSS feed or see this one first, the relevant first post will be along in a minute.

It is that time of year again – the jars are showing up on the store shelves, the rhubarb and strawberries and other foods are starting to come up at the garden, the farmer’s market. Most of us find that we can best afford the freshest and best food when it is abundant and in season – and that if we are to avoid waste and eat well during the cold or dry season when little is produced, we should take what is cheap, nutritious and plentiful, and put it aside now. This also allows us to get food that tastes like we want, that doesn’t have chemicals and preservatives we don’t want, and that our family loves. So now is the time to talk about food preservation of all kinds. Today I’m talking pressure and water bath canning.

Ok, Remember my emphasis on safety when talking about Water Bath Canning? Did you think I was anal then? You ain’t seen nothing yet. With water bath canning, there are a few things that can be dangerous – but mostly, the acidity will protect you from botulism. By definition, most of the things that you will be pressure canning can support botulism toxin – which means if you do it wrong, you and anyone who eats your food could die horribly.

Now I can imagine that there are some people who are just plain terrified, and don’t ever want to pressure can. But if you eat food from cans, you are eating food using the very same processes – that is, the canned pumpkin or soup you are eating has precisely the same risks and benefits that home canned food has (and, in fact, there was a botulism outbreak involving commercial foods last year). So the issue here is not “I should be afraid of pressure canning” but “I should be very wary and respectful of pressure canning, and make sure I do it *EXACTLY* correctly.” Because the truth is that properly canned food is safe. What I want to make clear is that cutting corners, or using older techniques your Grandma taught you, or just estimating is not sufficient in this case. I’m one of those estimating type of people – but I don’t do that when I pressure can.

Here are my rules for pressure canning:

1. No one pressure cans until they have water bath canned. Seriously, until you learn the basics of handling jars, filling them, creating a seal, etc… don’t start pressure canning.

2. Make sure you are up to date on your canning information – use only *CURRENT* canning instructions. You can use older recipes – or any recipe – but make sure that when you can the food, you can it using currently appropriate techniques for the ingredient that has the LONGEST canning time – that is, if you have a family recipe for meat sauce, can the recipe based on the meat, which is probably the thing that requires the longest canning time.

It is not sufficient to use the techniques your Mom or Grandma used, even though they never killed anyone. Grandma probably smoked during pregnancy and Mom may well never have even heard of a seat belt or carseat, but that doesn’t mean that just because you lived to adulthood, everyone did. The truth is that botulism is fortunately rare – but you still don’t want it. So even though Grandma knew best about a lot of things, you should can correctly. Your canning books must have water bath and canning guidelines written *after* 1994 – period, and you must follow those guidelines.

3. You should have a copy of the Ball Blue Book – a current guide to canning. I also suggest you take a look at this site for current, up to date instructions, but I strongly encourage people to get a copy of the CURRENT (or at least within the last few years – canning books written before 1994 are not safe!!!) Ball Book (usually available anyplace canning supplies are sold, or online) or the book that the site mentioned above is selling, because I think sometimes when you are in the middle of a big project, with your hands covered with stuff and water steaming out of a pressure canner, you might not stop to go online and confirm that it was, indeed, 12 lbs pressure, not 10. This is not acceptable – so have the book so you can just look it up, or please swear up and down that either you will look it up, even when it seems inconvenient, or just spend the $6 and get the book.

4. Please make sure you read through the instructions for pressure canning and genuinely understand them before you do it. No shortcuts – don’t just wait until the steam is kinda puffing out, but wait until it is steady. Don’t estimate times. Don’t decide that a lid that doesn’t quite fit is good enough. Do what they tell you.

5. Make sure your pressure canner (NOT a pressure cooker – you cannot safely can in a pressure cooker) has an accurate gauge. This is not a big deal if your pressure canner has a weighted gauge (the kind that jiggle and make tons of noise), but it is absolutely essential if you have a dial gauge – take it to your county extension office and have them check it once a year, and make sure you know your elevation and use appropriate pressure for that elevation. And if you have a dial gauge pressure canner, a study found that the standard should be not 10lbs pressure, but 11lbs – so if you see a recipe, even a recent one, that says “10lbs pressure” – put it at 11lbs.

If you buy a used pressure canner (and there are a lot of used ones out there), make sure you get a manual. While old pressure canners are much safer than old pressure cookers, there is still a lot of pressure built up, and if you don’t use them as instructed, not only could your food not be safe, but you could get a face full of hot steam (which will burn you) or even be injured by parts going flying. The companies that make pressure canners will have old manuals available, so if you buy a yard sale canner, the first thing you need to do is get the manual. The second thing is to have the gauge checked (worth doing once even if you have a weighted gauge) and to make sure that the gasket still fits tightly. If you see or feel steam persistently coming out along the gasket, you need a new one. You can order a kit from the company to fix it, or find a different pressure canner.

SIX THINGS YOU ABSOLUTELY MUST NOT DO WHEN PRESSURE CANNING:

1. No jars larger than 1 quart – the food can’t get hot enough to be safe.

2. Never reuse jar lids when pressure canning – ever. Make sure the bands aren’t too rusty and aren’t bent, because the jar won’t seal. Check the rims of the canning jars very carefully – nicks or bumps will ruin your seal.

3. Don’t use rubber jars or anything other than the 2 piece canning lids. TEST YOUR DIAL GAUGE CANNING KETTLE ANNUALLY – DON’T CAN UNTIL YOU HAVE TESTED. Test all new kettles BEFORE you use them, regardless of the kind of gauge they have. READ THE MANUAL – details vary a lot by brand.

4. Don’t raw pack unless you are sure it is safe – “raw pack” means put food in the jars that has not been cooked. There’s a general move in canning towards hot-pack only. That means that the food should go into the jars hot. You’ll see mixed recommendations about this – but it is always unsafe to raw pack: beets, greens of any kind, potatoes, sweet potatoes, squash, pumpkin, okra, tomato/okra mixes and stewed tomatoes, and honestly, it is safer not to raw pack at all. Research has found that hot packed foods are often better textured and flavored as well.

5. Make sure that your heat remains even (if using a woodstove), that your stove is safe to can on (if using glass topped stoves), and that you don’t begin counting time until the steam has been exhausting for 10 full minutes, and that you are present to ensure that there are no sudden drops in temperature or other mishaps.

6. Remove jars carefully – don’t bang them or tip them.

Honestly, if you find all this too overwhelming, no worries – human beings didn’t have pressure canning until fairly recently. You can preserve a lot of food by root cellaring, season extension, water bath canning of high acid foods, dehydrating, lactofermenting, preserving in salt, alcohol and sugar, and freezing. I encourage people to pressure can, I want people to try it – but if you don’t think you can do it correctly, you will be fine without it.

Ok, so here’s how you do it:

Most of it is the same as water bath canning – you check the rims, you make sure the jars are have been cleaned in scalding water (boiling the jars is necessary if you are pressure canning for less than 15 minutes, and recommended anyway) and are clean, and that lids have been simmered.

Make sure the food you are canning is really clean and dirt free (reduces the chance that you are putting a big helping of botulism, which lives in the soil, in your food). Use the recipe you have chosen carefully. You CAN safely reduce salt quantities when pressure canning – but not when waterbath canning.

Pack hot food into clean, hot jars (if you put it in cold jars you could have one explode on you). Run a clean spatula (plastic or wood, not metal) along the edge of the jar to reduce air bubbles, and add more liquid if need be to compensate after the air comes out.. Wipe the rim with a clean cloth to make sure that no food gets under it. Leave the recommended amount of headspace (ie, room for the seal to be made) – always a minimum of 1 inch when pressure canning, unless a current recipe says otherwise.

Put on the hot lid, put the clean, hot metal band on, and screw down firmly, but not so tightly that no air can escape.

Put in the rack and and relevant amount of water (this varies by brand, so read the manual) in the canner. Put the filled jars into the canning rack (never put any jars, using any technique, directly on the bottom of the canner). Screw the lid on the cannter tightly.

Make sure the petcock valves are open. Turn up the heat – and PAY ATTENTION. This is not something you can do while you do other things. Watch for the steam, and then start timing when the flow is steady. After 10 full minutes of steam steadily and rapidly coming out, the air trapped in the jars and canner should be exhausted. If the air isn’t properly exhausted, the pressure may be inaccurate and the food may not be safe.

After 10 minutes of steady exhausting, close the vent. Watch the pressure gauge until it reaches the correct pressure for YOUR ALTITUDE – if you live more than 1000 feet above sea level you MUST ADJUST THE CANNING PRESSURE to compensate. Confirm your elevation before you begin canning and refer to the USDA chart for what is appropriate for your canner – if you have a weighted gauge, you can’t adjust it finely, if you have dial gauge, you can, so it matters both where you live and what kind of canner you have.

When you reach the desired pressure, adjust the heat on your stove to keep it at the same level – if it goes over, turn the heat down (or bank the fire) a bit, if it is under, turn up the heat. Keep an eye on the gauge – I do dishes or other light work, but nothing very distracting.

You begin timing when you hit the correct pressure, and you must be certain you were at the same pressure level the whole time. When you have processed as long as required, take the canner off the heat, and let it cool. Leave the canner alone otherwise – don’t vent pressure or do anything else. It will take an hour or so to get down to normal pressure.

DO NOT open the canner until there is no steam coming out, even if you poke the regulator with a stick (not your hand). A face full of hot steam can burn you seriously – don’t mess with it – make sure there is no more left.

Open the Petcock valve SLOWLY AND CAREFULLY. Wait a bit, until the canner is even cooler. Unlock the canner lid and remove it carefully. Leave the jars alone for 10 minutes with the canner open, and use the jar lifter to carefully transfer them to a clean dishtowel, without tipping them. Allow them to cool undisturbed. You should hear the “ping” as the jars seal.

When they are entirely cool, check them for the seal. If you press down on the center of the lid and feel any give or movement your jar is not sealed, and you can either reprocess the food (go through precisely the same procedure again with A NEW LID) or you can put it in the fridge and eat it soon. You will lose a lot of nutritional value reprocessing, so I wouldn’t do this with anything like greens.

After 18 to 24 hours, wipe off the jars, remove the rings, label them and put them in a cool, dry place.

When eating pressure canned food, check it when you open it. If there is any reason for you to seriously doubt the safety of the food – if you don’t hear the popping sound that goes with a breaking vacuum when you open it, if there is an off smell, bulging around the lid, a vent of gas – throw it out, and not on the compost pile, but in the garbage. DON’T TASTE IT!!! Botulism has no taste or smell, but sometimes does cause bulging – but can exist simultaneously with other kinds of spoilage. THROW IT OUT IF THERE IS ANY DOUBT.

There are some things – darkened bottom lids, discolored peaches, a pinkish color on some fruits that are normal – they are chemical reactions to canning and are not signs of trouble. I won’t list them all, I again, reiterate this is why you should read the books and websites carefully and several times until you are familiar with the information.

The USDA recommends that you boil any food that has been pressure canned, or anything that might conceivably support botulism (including tomato products without added acid) be boiled at at a rolling boil in a covered pan for 10 full minutes – and 1 additional minute if you are more than 1000 feet above sea level for each 1000 feet or fraction thereof (ie, if you live at 2200 feet you would boil your for 12 minutes). Their recommendation is that it would be safest to do this every time, and that it should definitely be done if there is any doubt about your having used a safe canning technique. It should not be necessary if you have done everything carefully and precisely.

Canned food will keep for many years, as long as the seal is intact, although there is a gradual loss of nutrients. Jackie Clay at Backwoods Home regularly tests and uses canned food that is more than a decade old, but the general recommendation is no more than 3 years – but I wouldn’t hesitate to eat anything older, as long as the seal seems intact, there are no problems, and, more than five years out, I would boil it for the recommended time, just in case.

Happy Canning,

Comments

  1. #1 Kevin Wilson
    May 6, 2010

    Hi Sharon, I see the statement that “you cannot safely can in a pressure cooker” many places, but none of them explain why. Can you do so, or point me to an explanation?

    Thanks

    Kevin

  2. #2 Tsu Dho Nimh
    May 6, 2010

    Kevin – Some small “pressure cookers” do an excellent job of speeding up cooking by boosting the pressure inside the pan, but they can’t get the pressure high enough for safe “canning”.

    Fagor, for example, makes several pressure cookers that do 8PSI, which isn’t high enough to can anything I can think of.

  3. #3 speedwell
    May 6, 2010

    Sharon, I have a lot of trouble canning in pint jars. The jars (I can mostly salsa and related products like the Hungarian lecso) leak a lot while in the canner being processed. The jars do seal good and tight nine times out of ten, despite leakage. I do take care to wipe the jar rims well with a clean non-fuzzy towel before putting on the lids and tightening the bands to normal hand torque (about what you would use to close a mayonnaise jar).

    Could the leakage be due to not using enough headspace? Mom told me that the full inch was for quart jars, but I should use less for smaller jars.

  4. #4 speedwell
    May 6, 2010

    By the way, I wish you would say a few words about canning meats. Information on the Net is scant and contradictory.

  5. #5 Sonrisa
    May 6, 2010

    Ooops! I broke rule #1. We’ve been pressure canning for a while and I have never water bath canned, ever :o. At 5400 feet there isn’t much that can be WB canned though. Honestly, canning is my least favorite way of preserving. Too much “stuff” is needed, and it’s time and energy intensive. Unfortunately, If you want to keep meat for more than a few months without refrigeration it’s the best option. Luckily, drying can be done very quickly (even in the shade) here. We have very dry air (which is probably why I feel like a walking piece of beef jerky ;)). I do can tomato sauce and meats, but most things I try to find other ways to preserve. This year I want to try making tomato powder. The less I have to use the beast the better!

  6. #6 hat_eater
    May 6, 2010

    @1&2
    According do Wikipedia, “Most pressure cookers have a working pressure setting of 15 psi (approx. 107 kPa) over the existing atmospheric pressure, the standard determined by the United States Department of Agriculture in 1917.[2] At this pressure boost relative to sea-level atmospheric pressure, water boils at 122 °C (252 °F)”

    So are most pressure cookers OK for pressure canning (if you know the technical specifications of your particular model) or should they not be used because of other issues (or not holding true to their specifications)?

  7. #7 darwinsdog
    May 6, 2010

    My wife & I have been canning since the 1970s, and we routinely can in 1/2 gallon jars. Four at a time will fit in our canners. Never had a problem.

    We have never reused lids but this past year we have been carefully removing lids & saving them, with the thought of trying to reuse some of them this year. We remove them with a broad bottle opener so as not to bend or dent them. Those we do bend or dent we discard. Not sure how well used lids will seal but intend to find out.

    I would think that one could can in a pressure cooker, if the weight was heavy enough to build the required pressure. Our pressure cooker isn’t big enough to can in, though.

    If you chase the pressure up and down, which is all too easy to do on a woodstove, liquid will blow out of the jar. It’s necessary to give the process extra time to compensate for the time when the pressure drops too low but the jars will still seal & the contents be sterilized. The final product may be unattractive with half the liquid blown out but it is still edible.

    Clostridium botulinum is an obligate anaerobe endemic to the gut of equids. The clostridial endospores persist virtually indefinitely in soils where horses or donkeys have shat. They are so durable that they can withstand exposure to the cold vacuum and harsh radiative environment of space. The endotoxin this bacterium produces is so deadly that a kilogram of it would be sufficient to kill off the entire human population. Boiling water alone won’t necessarily kill the endospores, hence the need for pressure, low pH or highly hypertonic environment provided by high sugar or salt concentration.

  8. #8 Fatima
    May 6, 2010

    I love to make my own spaghetti sauce and would like to can it. I’ve tried to find info on pressure and times, but have been advised to follow the ball blue book recipe for sauce (by the ladies at our county extension office). Dang it, I like my recipe better! Do you know any guidelines? Thanks for the encouragement you are providing to all of us!

  9. #9 Sharon Astyk
    May 7, 2010

    Speedwell, the problem is probably either headspace, or possibly uneven heat – I’d go to the full inch and see how you do with it.

    The problem with most pressure cookers is that they aren’t sufficiently large to hold heat as long as a pressure cooker – if you had one as big as a pressure cooker lying around, you could probably do it, although I’d add a few extra minutes of processing time just in case, but it is much easier to purchase a pressure *canner* and use that for cooking (which is fine) than worry about making a mistake vice versa.

    What do you want me to say about canning meats, Speedwell? It is the same as processing anything else – follow the instructions. The National Center for Home Food Preservation will have the most current guidelines, but I’m happy to answer any specific questions.

    Fatima, it depends on what’s in your recipe. As long as you pressure can it at the time listed for the ingredient that needs the longest canning in your sauce (ie, if your sauce has mushrooms in it, along with tomatoes, you use processing times for mushrooms) you can use any recipe. If you want to water bath can your spaghetti sauce, however, and there’s more than tomatoes, sugar, lemon juice/vinegar and salt in there, you do need to use a recipe that was made proportionally to be water bath canned.

    Sharon

  10. #10 KC
    May 7, 2010

    I’ve had problems with leaking through the lids during boiling water bath. I eventually solved this by tightening the lids an extra bit tighter before placing them in the canner. I had tightened the lids, but turns out they needed to be another notch tighter. This solved it.

  11. #11 naturalmom
    May 9, 2010

    Hi Sharon, thanks for this. I’ve been pressure canning for a few years now. I have a questions that I’ve not been able to find an answer to. Maybe you (or one of your readers) can help!

    Is there any reason not to use a pressure canner for foods that *could* be processed in a water bath? The Ball Blue Book does not give pressure canning times for, say, peaches. Not surprising, since most people don’t pressure can. What *did* surprise me, however, is that the booklet that came with my pressure canner also only gave water bath instructions for peaches. Sometimes I prefer to use the pressure canner because it uses less water, holds more jars (fewer batches), and doesn’t steam up the kitchen as much. Last year I just estimated, which you say not to do, but I estimated on the long side and they were fine. But I still wonder: is water bath *better* for acidic foods for some reason? If not, do you know of a book or website that gives pressure canning times for acidic foods such as peaches, apple sauce, tomatoes, etc.?

    Thanks

  12. #12 naturalmom
    May 9, 2010

    Speedwell, in addition to not enough head space, I believe not properly venting the air bubbles can also be a cause for leaking. I’ve forgotten to vent a couple of times and had excessive leakage on those occasions.

  13. #13 Jenn
    September 26, 2010

    Thank you for the insight. I am pressure canning for the first time as I type this and my question is: if I’m chasing the pressure (it seems to be falling to 8 and then climbing to 12 and back down again) is it safe to just add some time extra time? If so, how much?
    thanks!

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