Pressure Canning 101

Sharon July 24th, 2008

Ok, Remember my emphasis on safety when talking about Water Bath Canning last week.  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.

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 a new kettle BEFORE you use it.    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,

Sharon

34 Responses to “Pressure Canning 101”

  1. Rosa says:

    Why do you say it’s not safe to can in a pressure cooker? I have a 15 pound pressure cooker that seems to be just like a weight-top pressure canner, only smaller.

  2. Fern says:

    I cheated, and started my canning with pressure canning and not water bath canning. HOWEVER – I pressure canned ‘regular’ tomatoes only that year, thus was working with high-acid food that wouldn’t support botulism.

    Since I get many of my jars from freecycle or garage sales, at least one jar in 12 ends up not sealing or being culled for chips. Marked with permanent markers and warning labels I use them for dry storage, refrigerating leftovers, etc (and use ‘used’ lids on them then).

  3. Kelsie says:

    Thank you SO MUCH. This was extremely informative, cut-and-dry, and firm, but not fatalistic–in other words, exactly what I’ve been looking for. :)

  4. lissa says:

    rosa,
    current recommendations are that if you cooker/canner will not hold at least 4 one-quart jars, then it will cool down and drop pressure too quickly, which effects the overall time the food is under pressure. so if your ‘cooker’ has regulators (weight or dial) that measure at least 5-10-15 lbs of pressure, and will fit at least 4 quart jars, it can be safely used for pressure canning. if not, then don’t risk it.

    lissa

  5. MEA says:

    There are pressure cookers/canners in one.

  6. Sharon says:

    Rosa, the size of the pressure cooker is the problem – they cool down too quickly, and lose heat too rapidly to be sure that food is getting hot enough, and it can cool down too quickly, leaving food that isn’t safe – pressure canning times include the cool down. _Stocking Up_ and the USDA say “just don’t do it” – _Putting Food By_ suggests you can do it if you add at least 5 minutes to the venting time, 10 minutes to teh processing time, don’t use anything bigger than a pint, are below 1000 feet and have a weighted gauge that can get to 15 lbs pressure. But I honestly don’t think it is a good idea even then – pressure canners aren’t that expensive or that hard to find. The vents and gauges are different, and may involve losing more pressure and heat than we think, even if the gauge is checked. Lack of precision is not a problem in cooking, but it is in canning. Also, if you live above 2000 feet, you cannot use these because their capacities aren’t big enough – the appropriate amount of water will evaporate before you can achieve safe canning.

    Sharon

  7. Sharon says:

    You can pressure *cook* in a pressure canner. You cannot pressure can in a pressure cooker – anything designed to be both must be first a canner – but yes, most canning companies advertise them as both.

    Sharon

  8. cb says:

    When she heard the “ping”, my mother used to say “well, there’s one if we never get any more.” Last week, I heard my granddaughter say the same thing. Ah, sweet.

  9. Ailsa Ek says:

    I have a stupid question: what changed that they had to come out with new rules? I grew up eating jams and jellies canned in plain supermarket jars with paraffin on top and my siblings and I are fine. My grandmother canned pickles in the glass jars with glass lids and nobody died. Why can’t I do it that way now?

  10. cb says:

    Well, for one thing, many foods are less acid than they used to be. I have another food rule–if my chickens won’t eat it, neither will we. (Grocery store cherry tomatoes compared to heritage volunteer seeded ones; or grocery store “organic” strawberries compared with those out of my garden.) Why won’t the chickens eat these foods? GMO? Irradiated? Old?

  11. Sharon says:

    Well, part of the problem is that some foods, including tomatoes, are less acid than they used to be – they’ve been bred for lowered acidity. But the real difference is that we’ve learned more about botulism, anaerobic conditions and the situations that can enable them. In the early 1990s, the USDA revised its canning rules based on a decade of extensive testing – the rules didn’t make it into all the major canning books, though until the mid-1990s.

    The thing is, this is like driving with no seat-belts, or smoking while pregnant. People used to do it all the time, and you can be pretty sure that if your Grandma is still alive, she did drove without seatbelts and survived. Lotsa babies were born to mothers who smoked when pregnant – and it is impossible to tell with pure anecdotal evidence that the babies from those Moms really were smaller, more likely to be premature, more likely to be unhealthy, more likely to have asthma, more likely to die of SIDS. In order to figure that out, a big study had to be conducted under rules of scientific research – the same is true about canning – until people did the research, for example, they didn’t realize that occasionally molds can reduce the acidity of even high acid foods, and allow them to grow botulism if they aren’t properly canned.

    I ate those foods too – but that doesn’t mean that everyone did it and lived – there were cases of botulism that didn’t have to happen. There were cases of food poisoning that didn’t have to happen. Just as people got maimed and died that didn’t have to before, just as babies died of SIDS that didn’t have to. The odds are that if you did this, you wouldn’t die, and your family wouldn’t die. But the blunt truth is that the chances that you or someone you love might die from botulism are low but not nil – and it is a bad, horrible death. There is no reason to risk it – period. Better to skip canning altogether and use other techniques.

    Sharon

  12. [...] Casaubon’s Book » Blog Archive » Pressure Canning 101 Ok, Remember my emphasis on safety when talking about Water Bath Canning last week. 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. R.E.A.L. Survivability: Environmental Genocide July 24th, 2008 [...]

  13. Rosa says:

    Thank you for the pressure cooker stats, Sharon & Lissa.

    That’s a bummer, though – it seems a shame to run the canner for just a few pints of beets or applesauce, and I am finding it really difficult to find time for whole big batches this year. I was really hoping to be able to run a few pints in the pressure cooker while I make dinner every night (my stovetop is small, so if my canner is on the stove my frypan can’t be – just a small pot for heating water for lids & warming jars.)

  14. Mary says:

    Thank you for a wonderful post, Sharon!

    I just popped over to Amazon to order a few books ;-) I’m very interested in lactofermentation and other low-energy forms of food preservation, but I also love my canned tomatoes!

    You’ve inspired me to think outside of the consumer box and try many foods that I’ve been convinced I didn’t like for so many years. Turns out I just don’t like the commercial versions.

    Thanks!

  15. lissa says:

    rosa,

    i know what you mean. i hate to run the canner for 3 or 4 pints… there are a couple of options i use. sometimes i just freeze what i have until i have enough of something else to take up the extra canner space…. as long as all the jars in the canner require the same amount of time under pressure, there’s no rule stating they all have to be the same thing. for example, if i have a few quarts of spaghetti sauce with ground beef, and a few quarts of meatballs, they all need to be processed using the guidelines for beef, so can all go into the canner together. the other option i sometimes use is to fill the empty space with jars of water. once processed and sealed, you have jars of sterilized water for storage.

    lissa

  16. Christina says:

    You’ve said you use a Kuhn Rikon, but they don’t manufacture a pressure CANNER, just pressure COOKERS. That means they only measure 8lbs and 15lbs of pressure. How are you pressure canning with that? I have a large KR pressure cooker, and I’m trying to figure out if I can use that for canning or if I need new equipment…

  17. Duke says:

    I have a 2 questions

    1st is botulisum found in canned food that the lids are still firmly sealed? Meaning can I rely on the fact that my canned goods are ok as long as I have a solid seal on them?

    2nd when I do my tomatoes and I process using the weighted gauge and cook it for the alotted time, my bottles come out with alot of the fluid gone from the jar and my tomatoes really look over cooked and over pressureized. Is that telling me the times or pressure that I am using from the recipe are to much?

    Thanks Duke

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  20. lesli says:

    Hi, I have a new pressure canner and would like to use it for the first time. I have been looking at it and trying to build the courage.

    Thank you for the GREAT 101 at the beginning of the site. I had read many articles, chapters in current books – and yours was the best.

    I would like to try with something easy. Split peas soup or Vegetable Beef Soup.

    Do I use my old standard recipe for these two favorites?? Then when hot follow your instructions for the processing??

    Please advise. I have done water canning before so I am not completely terrified :0)

    Just looking forward to trying soon and enjoying the pleasures of having my food “put up” for convenience.

    Thanks……..

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  29. Jerry says:

    Isn’t the toxin destroyed if heated at a high temperature for a few minutes? The spores survive, but shouldn’t be a problem for an adult. I know of people who have eaten food conserved in this way without even reheating the food – although they are now supposedly more careful. They did not use a pressure cooker, they simply boiled the food into glass jars with rubber rings between the lid and the jar for at least sixty minutes, creating a vaccum and letting the food last, in their words, indefinitely. They had also tried this with metal-lidded jars and more modern jars with hinged lids.

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  33. Lance Staub says:

    I am asking the same question that Christina did back in 2008.

    I know that my KR only has the 8# & 15# settings but if I used the 15# setting which is suppose to get to 254 deg feh, why would that not work. OR, is the pressure TOO great. KR states that they DO NOT MAKE a pressure canner! I did by mine to can with because I was reading all kinds of comments on the web about it doing the best job. It should at $400! Does anyone have a good answer to Christina and my questions?

    “You’ve said you use a Kuhn Rikon, but they don’t manufacture a pressure CANNER, just pressure COOKERS. That means they only measure 8lbs and 15lbs of pressure. How are you pressure canning with that? I have a large KR pressure cooker, and I’m trying to figure out if I can use that for canning or if I need new equipment…”

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