Monday, May 18, 2009

Home Canning: What about Botulism?

I had planned to write a post about botulism next month, when I get more into canning low acid foods. Due to comments and e-mails from people that are afraid of poisoning somebody, I decided to move up the date.

Of all the unwanted organisms that might live on your food, the Clostridium Botulinum bacteria has to be the scariest. You can't see it; you can't smell it; and you can't taste it; yet it can kill you. Talk about scary.

So how do you protect yourself?

Once again, I will divide foods into two categories, high acid foods (food with PH below 4.6 such as pickles and most fruits) and low acid foods (food with a PH above 4.6 such as vegetables and meats).

High Acid Foods

For high acid foods, my discussion is short. Clostridium Botulinum will not grow in these food. If you have been afraid to can these foods, for fear of botulism poisoning; relax, breath a sigh of relief, and start canning. Just remember, that while bacteria will not grow in these foods, mold and other fungi will, so be sure to process your food in boiling water for the length of time specified in the recipe. The heat from the boiling water is necessary to destroy mold.

Low Acid Foods

Now we get into a discussion of why I keep emphasizing that low acid foods need to be processed in a Pressure Canner. The reason I go into details of what can go wrong is not to scare new people away from canning, but to give you enough information that you are prepared to can food safely.

Let's say you pick some green beans from your garden or buy some ears of corn from the farmers market. This food is bound to have dormant spores of the Clostridium Botulinum bacteria on it. These spores are so common that their presence is inevitable. The reason why they are in their dormant state is because they need a low oxygen environment. As long as they are exposed to air, they must remain in their dormant state.

Even after you wash your food, some of these dormant spores will remain on the food. It is nearly impossible to wash them all off. Fortunately eating these dormant spores, does us no harm. You eat the all them time, you just never knew it.

Now let's say that you decide to can this food. Let's also say that for whatever reason, you did not process it at the proper pressure for the proper length of time to ensure that all the spores are destroyed.

Now you sit your jar of food on the shelf to eat later. These spores are now sitting in a cool, moist, low oxygen, low acid environment. This is just the environment they have been waiting for. They come out of their dormant state and start actively growing. As the bacteria grows, it release a chemical that is toxic to humans. In as little as 3 days, your jar of food will be poisonous.

OK, I Know That I Need To Use A Pressure Canner, But I Am Still Scared.

Now let's say that you were very careful to process the food at the specified pressure for the specified length of time, but you are still worried that one of those spores might have some how survived. How can you tell?

The bacteria doesn’t discolor your food, or cause a funny odor, but it does still give its presence away. As it grows, it releases a gas which loosens the seal on your jar. In a properly sealed jar, you should need a jar opener to get the lid off. You should not be able to pull it off with your fingers. Any jar with a loose seal, should be considered contaminated.

As I said before, the reason I wrote this is not to scare people away from home canning, but to encourage people to practice safe canning. A lot of research has been done over the years. We now know much more than we once did about what canning techniques are safe and what techniques are not safe. If you take advantage of what has been learned, home canning can be a very rewarding experience.


  1. Is there a particular brand of pressure cooker that you like? What do you look for when you buy one? It's the pressure cooker that scares me the most. I'm always afraid of it exploding or something.

  2. Modern pressure canners are very well built. As long as you follow instructions, they are also very safe. Be sure to read the instructions that come with your canner. Always fasten the lid properly, and always let the pressure gradually return to zero before you take the lid off.

    The main thing I would look for is the size. Your everyday pressure cooker might only be big enough to fit a pot roast. If you are serious about canning, you want on that is big enough to hold several quart jars. These larger ones usually say "canner" rather than "cooker." The word tells you that it is big enough to hold canning jars.

    I can remember my mother canning food in a small pressure cooker when that was all she had. She could do 4 pint jars at a time. It was slow, but it worked. Eventually she found a canner at a garage sale that she could afford.

    In some canners the pressure is regulated by a dial guage, and in some it is regulated by a weight. The dial is probably easier to use, but the gauge shuold be tested every year to ensure that it is still accurate. There are places that do this testing for free.

    I personally like weighted regulators just so I don't have to mess around with taking the gauge off every year and mailing it in to have it tested.

  3. This was a very informative post. You know so much about every aspect of canning. Very impressive.

  4. Charlotte, thank you for taking the time to answer my question. I've only "canned" an apple jelly and a grape juice jelly (recipe from high school 30 years ago!) but putting up (as my grandmother would've said) anything else is all so new and exciting and a little scary. Having you here is a godsend. Thank you!

  5. Thanks for the info. Do you know where I can buy an new pressure gague? Mine was dropped and the front casing gets moist so I can't read the numbers. I would rather buy a new one than take chances with one that was dropped and is cloudy.

  6. I would start by looking in the instruction booklet. They usually have information about replacement parts. I found several just now by typing "pressure canner gauge" into google and then clicking on "shopping results." You need to know your model to get the right size.

  7. Botulism is my number one reason for staying away from canning - even if the idea has taken hold. And am afraid of pressure cookers! (I'm also afraid of deep-fryers). I have a lot of fears for a cook. This blog is very helpful as to the ins and outs of the process.

  8. Well, Claudia, you could always try your hand at jams and pickles. With them, you don't have to worry about botulism, and you don't need to use a pressure cooker.

  9. I've have a few jar of jam I have made and I processed in a water bath. Some of the lids can come off by prying with my fingers. Would that be cuz I didn't process them long enough? Should I throw those kind of jars out or are they safe cuz they're jam???

  10. Megan,

    Jam is high acid, so botulism bacteria can't grow in it. If you keep the jars in your refrigerator, they should be fine.

    As for why you didn't get a tight seal, the processing time could be a factor. The amount of headspace could also play a role. If the rim wasn't clean, that can interfere with the seal.

    Sometimes we just don't know why some jars don't seal well. Hopefully most of the jars sealed. If it was only a couple of jars that didn't seal tight, I would just chalk it up as "one of those things"

  11. This is an excellent site! I have been canning just about everything I can get my hands on these days. However, I have had real issues with green beans -- three series have gone bad -- I am now using my Grandmother's pressure canner [holds 7 quarts at a time] == last night yielded the first set and they seem to be off color -- should I toss them and go back to freezing? Thanks!

  12. Hi I am fairly new to canning and have done most high acid foods but I did do spicy dilly beans and I did a water bath, for the time ball blue book said, is this safe because it is pickled? or in vinager?? I hope so because I made like 35 cans...

  13. Okay I just read your pickled recipe for canning beans, thats good news!! I really like your site I am going to try your pickled aparagus soon:)


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