Botulism is a serious food-borne illness that can develop in home canned foods. Learn what you need to know to ensure you’re creating a safe product while home canning, and protect your family from the threat of botulism.
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There’s a lot of unsafe canning and home food preservation advice out there. And I mean A LOT.
With the Internet and social media what it is today, it’s easier than ever for anyone to share anything online, and it’s more difficult than ever to weed out the fact from the fiction and the good advice from the bad. While that can be frustrating at the best of times, it can actually be deadly at the worst.
Right now, as I write this, it’s mid-September and we’re in the thick of canning and preserving season. So naturally there seems to be more bad advice circulating about home canning and food preservation than at any other time of year, which is what made me decide to write this post today. Because while I am a HUGE proponent of preserving food at home, I’m also a huge proponent of not dying or poisoning your entire family. And I have a feeling you probably are too.
Still, there’s a lot of controversy when it comes to home canning and food preservation. There are people who believe that today’s safe canning guidelines and list of do’s and don’ts is some sort of conspiracy to scare people off from being self-sufficient. There are many others who argue that their mothers or grandmothers did it a certain way (that is no longer recommended) for years and never had a problem, so they continue to do it the same way even if it’s deemed unsafe by today’s standards. Still there are others who simply don’t know what dangers may be lurking in a jar of improperly home-canned goods, or who don’t understand the science behind home canning, PH levels and food-borne illnesses.
Unfortunately when it comes to home food preservation, what you don’t know can hurt you. In fact, it can kill you. Therefore it’s of utmost importance that you follow safe, up-to-date advice and stick to tested recipes and methods of home food preservation, because not doing so can put you and your family at major risk of contracting a deadly illness: botulism.
Let me be clear about this: I am not trying to scare you. Rather, my goal is to empower you with knowledge so that you stay safe and keep your family safe while preserving healthy, homegrown, homemade foods with confidence.
That being said, lest you roll your eyes and tell me I’m over-exaggerating, let me present you with a few facts about botulism…
Some chilling facts about botulism
- Botulism is a serious illness that’s produced by Clostridium botulinum bacteria, which, when activated, produces a neurotoxin that can paralyze and even kill its victims.
- Botulism is the most deadly toxin known to man, and just a single gram is enough to kill over a million people (source).
- Due to its extreme toxicity and lethality, it has actually been weaponized and used in warfare as a bioweapon.
- Botulism can be contracted through contaminated foods, wounds, and through inhalation, (although for the sake of this article we are focusing on food-borne botulism).
- The number one way that people contract botulism in the U.S. is by eating contaminated home-canned foods that have been improperly canned. Improperly-canned vegetables are the most common cause of botulism from home-preserved foods (source).
- Other common sources of food-borne botulism include garlic and herb-infused oils, baked potatoes, cured meats like sausages and ham and canned and fermented fish.
- Botulism is odourless and flavourless, and does not typically cause any visible signs of contamination or food spoilage (making it all the more insidious and hard to detect in preserved and home-canned goods).
If that’s not enough to make you think twice about using grandma’s canning recipe, consider the following…
Symptoms of botulism
Symptoms of food-borne botulism include:
- Vomiting, nausea and diarrhea
- Double vision and/or blurred vision
- Drooping eyelids
- Symmetrical muscle weakness on both sides of the face
- Dry mouth
- Trouble breathing
- Trouble swallowing
- Slurred speech
- Paralysis
If left untreated, botulism can be a deadly illness, although if caught early, an anti-toxin is available and can stop the spread of botulism and paralysis. There is currently no vaccine to prevent against the botulism toxin.
For survivors of botulism illness, recovery often takes weeks, months, or even years. One man who contracted botulism after he cut the processing time short on his home-canned venison never regained his sense of taste. Others have had to relearn how to walk and/or have lost full mobility.
Suffice it to say, it’s a serious illness and should be taken seriously.
All of that being said, there is absolutely nothing to worry about so long as you follow safe canning guidelines, procedures, and tested recipes.
So, what do you need to know to make sure you never have to worry about botulism in your home preserved foods??
First of all, you need to understand the science behind safe home food preservation (the canning process specifically) and botulism.
The science behind botulism and safe home canning
First of all, you should know that botulism spores are everywhere. They’re in the soil, in our intestines, on our fresh vegetables and meats, in the water and probably at the top of Mt. Everest too. But they’re dormant unless they are allowed to germinate and produce toxin under the right conditions.
So, what are the right conditions for the botulinum toxin to form?
Botulism spores germinate and grow in moist, low-acid, anaerobic (low or no oxygen) environments at temperatures between 40º-120ºF (5º-49ºC). Yup, the exact conditions in the jars of low-acid home-canned foods sitting on your pantry shelf.
Sealed canning jars packed with low-acid foods like green beans present the ideal environment for botulism spores to germinate and become deadly.
Botulism spores cannot be killed in boiling water bath canners because the water doesn’t get hot enough to kill the spores (water boils at 212ºF/100ºC). However, botulism spores can be killed by heating to upwards of 240ºF/116ºC with the use of a pressure canner.
So, that being said, here are the cardinal rules of home canning that you must know and follow to ensure a safe product…
6 cardinal rules for safe home canning
There are a few cardinal rules when it comes to canning and preserving food at home that, when followed, make preserving food at home a safe, healthy and great way to feed your family, save money and avoid food waste. Here are the top 5 rules you must always follow:
Rule #1: Low-acid foods MUST be pressure canned.
While high-acid foods (including most fruits, jams, jellies and pickles) can be safely canned in boiling water bath canners, all low-acid foods (including meat, poultry, seafood and vegetables that are not pickled) must be pressure canned.
Low-acid foods are foods with a PH higher than 4.6. This includes meat, poultry, seafood and vegetables that are not pickled. So, for example, you could safely water bath can pickled green beans, but you must pressure can regular green beans that have not been acidified with vinegar.
One of the most common causes of botulism from home canned foods is not adhering to this simple rule.
ALWAYS use a pressure canner when canning low-acid foods like meat and vegetables.
In 2015, more than two dozen people became ill and one person died after eating potato salad made with improperly home-canned potatoes at a church potluck. According to a report from the Centers for Disease Control and Prevention, “the attendee who prepared the potato salad with home-canned potatoes reported using a boiling water canner, which does not kill C. botulinum spores, rather than a pressure canner, which does eliminate spores.”
Moral of the story? Always, ALWAYS pressure can low-acid foods. I’ve seen some people argue that their family has been water bath canning green beans (or peppers or tomatoes… which we’ll get to in a minute) in a boiling water canner forever and has never had a problem. But just because you’ve never had a problem before doesn’t mean you can’t have a problem in the future.
When we’re talking about an illness as serious as botulism, why take the risk?
Rule #2: Follow up-to-date canning procedures
Proper canning procedures include washing and sterilizing bands & jars before filling them, always using new lids and and always processing jars of food in a boiling water bath or pressure canner (according to food type) as opposed to oven canning, open-kettle canning (putting hot food in jars and letting the lid seal on its own) or inversion canning (flipping the jar upside down to seal the lid).
Again, just because you or your mom or your grandma have always done it this way doesn’t mean you should risk it going forward. It’s so easy to just put the jars in the canner, why not make sure you’ve got a safe finished product to enjoy and share with your loved ones?
Rule #3: Always follow a tested canning recipe
Canning is a science, not an art. While I encourage you to get creative in the kitchen when it comes to preparing meals from scratch, when we’re talking about food preservation, you can’t just wing it.
While it is possible to put your own spin on home-canned goods, such as adding or adjusting things like sugar, spices and dried herbs in small amounts, for the most part you need to follow tested recipes to a T to ensure they are safe.
This means you can’t skimp on the amount of vinegar or lemon juice you use in a canning recipe, you can’t cut the processing time short and you can’t just add any ingredients you like to a canning recipe and assume it’s still safe.
My go-to sources for safe, up-to-date, tested canning recipes are the National Center for Home Food Preservation and the Ball Complete Book of Home Food Preserving.The Ball Blue Book is also a highly respected and reliable source for safe canning recipes.
Of course, the canning recipes on this site are also safe, tested recipes that have all been adapted from the above sources. Some may contain less sugar, a different type of 5% acidity vinegar or an additional spice or flavouring ingredient (like the vanilla in my Strawberry Vanilla Jam recipe) but these are all safe adaptations. As you get more comfortable with home canning you learn the small tweaks you are able to make in a recipe and that’s the margin that allows for some creativity. Otherwise, your best bet is to do things by the book.
Rule #4: Tomatoes are considered a low-acid vegetable
This “rule” is actually one of the most contentious and controversial ones in canning circles these days. Just as there is debate around whether tomatoes are a fruit or a vegetable, so too is there debate over whether they are considered high or low acid.
Here’s the deal: tomatoes have historically been considered a high-acid fruit/vegetable (we’ll leave that debate for another day;), but due to hybridization over the years they have become less acidic. At least, that’s the story, In truth, even many of today’s heirloom varieties are low acid.
It’s difficult to know exactly which varieties fall just above or below the acidity limit of 4.6 on the PH scale, so to be safe, you should always assume that tomatoes are low acid and process them accordingly. This means either adding lemon juice or vinegar to home-canned tomatoes or tomato sauce when water bath canning or pressure canning them. Again, stick to tested, up-to-date recipes and you’ll be fine:)
Rule #5: Memorize the “Do Not Can” list
There are a few items that just CANNOT be canned safely at home, and those items include
- eggs
- dairy
- wheat/flour products (ie. noodles)
- pumpkin purée and pumpkin butter.
- nut butters
- fats, oils and oil-based products (ie. pesto)
I know there are people out there who have consumed home-canned milk and pickled eggs and pumpkin butter and even regular butter and who have lived to tell the tale, but this is another thing you just don’t want to risk.
While it’s possible to can pumpkin in cubed form, it is NOT safe to can pumpkin purée or pumpkin butter.
In lab tests, it was impossible to kill all of the botulism spores in the above products using a home pressure canner so there is no safe, tested way to can these items at home. If you’re wondering why you can buy cans of pumpkin purée and chicken noodle soup at the store, it’s because commercial canners can get up to higher temperatures than home pressure canners and can penetrate and kill all of the botulism spores.
In the case of canning noodles, it’s also a quality issue as noodles will be turned to mush in a pressure canner. Don’t ask me how they preserve the integrity of the noodles in commercial canning, but if you have any clue I’d live to know so leave a comment!
Rule #6: When in doubt, throw it out
The most cardinal of cardinal rules when it comes to home food preservation: when in doubt, throw it out!
If a jar of food is leaking, has lost more than half the liquid, looks moldy, smells bad or you’re not sure how it was processed (ie. a jar of home canned green beans from a friend), don’t risk it.
Also, remember that botulism is often odourless, flavourless and invisible to the naked eye, so don’t rely on these senses to tell you whether a jar of home-canned food is good or bad. If you have any doubts about the safety of your home-canned goods, toss it. It’s just not worth the risk.
Other considerations
Remember how I mentioned earlier that other common causes of botulism illness include baked potatoes, fermented fish and infused oils (among other things)?? Well, keep that in mind when preserving food in other ways at home too.
In the case of baked potatoes, do not store cooked, baked potatoes in aluminum foil as it creates the type of anaerobic environment that botulism loves. And store in the refrigerator (not at room temperature).
In the case of fermentation, it’s nearly impossible to get botulism from most fermented foods because they’re exposed to oxygen and are highly acidic. However there have been a number of cases of botulism caused by improperly fermented fish in Alaska, by and large involving traditional native foods like fermented fish heads, seal oil, fish eggs, beaver tail and even beluga flipper. So maybe steer clear of those foods?? I would. But then again, I’ve never had fermented beluga flipper. Done correctly, I’m sure it’s a delicacy and a half;)
Finally, do not infuse oil with herbs and/or garlic at home. Or sun dried tomatoes or peppers or anything else. Oil provides the perfect anaerobic environment that botulism loves to grow in, and garlic-infused oil has been the culprit in a number of cases of botulism, including this one from 1989.
It is possible to infuse garlic and certain herbs (including basil, oregano and rosemary) in oil for consumption, however you must immerse them in a 3% solution of citric acid and soak them for 24 hours before infusing them in oil. For more information, read this guide to making garlic and herb-infused oils at home.
Oh, and while it may be obvious, I just want to be clear that there is no risk of botulism in frozen or dehydrated foods:)
Knowledge is power
I must reiterate, none of the above is meant to scare you away from home canning and food preservation. On the contrary, it’s meant to educate and empower you!
With all of the bad and, most importantly, unsafe advice floating around the Internet these days, I thought it was important to clear up some of the misinformation out there.
At the end of the day, only you can decide what you feel comfortable with. Nobody can tell you how to run your kitchen or what you can and can’t do with your food. However I strongly advise you to follow up-to-date canning and food preservation safety rules and tested recipes to ensure a safe finished product for you and your loved ones. After all, isn’t the point of preserving food at home to be able to provide our families with healthy, homemade, shelf-stable food all year long?
There are lots of other ways to be a rebel in the kitchen (if you read my About page, you’ll see why I think preserving food and homesteading in and of itself is a form of rebellion!) But playing fast and loose with your canning recipes and procedures is a little like playing Russian roulette: you might be fine five times out of six, but that doesn’t meant the bullet will never get you.
Play it safe, follow tested recipes, use the proper canning techniques and equipment and don’t cut corners. And enjoy safe, delicious, healthy home-canned goods for many years to come:)
For more information on safe home canning, check out the following posts:
To make sure you always have a trusted source of safe home canning recipes on hand, I highly recommend the Ball Complete Book of Home Preserving or the Ball Blue Book.
Wanna learn how to can your own food?
Whether you’ve never canned anything before or you’ve done a little home canning and you’re ready to take the next step, my Yes, You CAN! complete home canning course will walk you through everything you need to know to get started canning food SAFELY at home.
Over the course of 12 easy-to-follow lessons, we cover both water bath canning and pressure canning, and I show you step-by-step how to can your own jams, jellies, pickles, pie fillings, fruits, vegetables, tomato sauce and chicken stock at home. And of course we’ll go over safe canning practices, equipment and over all best practices in more depth so that you always feel confident both during the canning process and while enjoying your home-canned food afterwards.
You’ll also get a collection of bonuses including:
- Printable checklists and cheatsheets to help you stay safe and never miss a step while canning food at home
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- A copy of my Home Canning Handbook, complete with 30 of my favourite home canning recipes for canning everything from fruits and vegetables to jams and jellies to sauces and salsa to stocks, soups, meats, combination meals and more!
If you’re ready to get started home canning (or canning more food than ever before this year!) enroll now and get started stocking your pantry!
I hope to see you in class!
Wishing you homemade, homegrown, homestead happiness 🙂
New to canning this year! My husband and I was loving it, however we did not know or indulge the vinegar or lemon juice rule with our tomato sauce canning…wondering if all our hard work is ruined now??
Hi Erika! This is a tricky one – adding additional acid to home-canned tomatoes is a relatively recent safety measure recommended by the USDA now that there are so many different varieties of tomatoes and some of them have lower acid content than others. I would do your own research on the subject and gauge your own comfort level when determining how to proceed, however tomatoes on their own are no longer considered safe without additional acidification.
If they were just freshly canned (within 24 hours) you can also just store them in the fridge and use them over the next few weeks, OR you can also open them up, put them all back into a pot, add the appropriate amount of additional acid, and re-process them with fresh lids (also within that 24 hour window).
For further information, please visit this website: https://nchfp.uga.edu/how/can/general-information/ensuring-safe-canned-foods/
-Ashley (assistant)
Hi Anna,
Does it make a difference when it comes to either water bath or pressure canning. Can you err on the side of caution and just pressure can everything?
Hi Heather,
Some food is better off water bath canned as the pressure from a pressure canner could cause the food to break down and destroy the quality of certain foods (ie. jam will break down and will end up to runny, pickles will be too soft, etc.) The headspace would also be different (all pressure canned food calls for a one-inch headspace, which is up to 4 times more than some water bath canned foods. The pressure could also cause siphoning and liquid loss of certain foods. So the short answer is, if it’s an acidic food that calls for water bath canning, stick to water bath canning it. If it’s a low-acid food that calls for pressure canning, always pressure can it.
Aloha Anna,
Your article has been so helpful! I’m wondering if you can help me with a jam water bath canning inquiry. I have not found many recipes for safe canning fresh mango jam. We grow our own mangos and have used 2 recipes both low sugar.
With 6 cups of mango chunks we use 4 cups of sugar and low/no sugar pectin. In one recipe we use 1/2 cup of fresh passion fruit juice and 1/4 cup bottled lemon juice. We have been using this recipe for some time now. However, we do not always have access to the passion fruit juice.
When there is no passion fruit juice available, we have used 1/2 cup fresh lemon juice and 1/4 cup fresh orange juice. But the jam turns out to be much too acidic from the lemon juice. My question really is, how much fresh or bottled lemon juice do we need to make a safe batch (8 jars, 8 ounce each) of jam the using just lemon juice?
Thanks for any assistance you can provide. We think that using this much lemon juice may not be necessary.
Mahalo!
Kiyo
Hi Kiyo, thank you for your comment! Great questions all around. Mangoes are tricky when it comes to canning – they lose their acidity when they ripen, so it’s actually not recommended that ripe mangoes be canned at all. Most recipes call for green mangoes.
While I can’t answer your question directly (that’s why finding tested recipes can be so tough!) I did find an excellent article with a few great recipes here: Preserving Mangoes
The NCHFP also has a recipe for a mango sauce, which I know isn’t quite a jam, but I thought was worth sharing anyway.
Best of luck and sorry I couldn’t be more help!
-Ashley
Assistant
My potatoes I don’t reassure canned last year were with no extra fluid added so the liquid level is low. You say if low fluid throw it out. Should I eat
These potatoes?
I am new at canning. I pressure canned some potatoes last year. The recipe called for no extra liquid and there is not much liquid in these jars. You say if there is low fluid don’t take a chance but throw it out. Should I worry about my potatoes?
Hi Glenda – according to this page and recipe from the National Center for Home Food Preservation, potatoes should be canned in water. Dry canning of potatoes is not recommended as a safe practice due to the risk of botulism.
https://nchfp.uga.edu/how/can_04/potato_white.html
You can also find more information about liquid loss here:
https://www.healthycanning.com/loss-of-liquid-during-home-canning/
As stated in the blog post, when in doubt, throw it out. It’s not worth the risk for a few potatoes.
Hi. I canned several pints of pickles with no issues. I felt the top of the lids and they were not popping up. After 2 days I was wiping the tops and one of them popped. I am not sure which one. Are they safe to eat ? So upset
Hi Pam – you should be able to tell which jar unsealed by looking closely at the tops of the lids – the one that “popped” / unsealed should be sticking up a little bit. Safe canning rule number one is always “when in doubt, throw it out”…don’t be too hard on yourself if you have to lose a jar or two. You’ll continue to learn more as you go!
Here are some links to further information:
https://nchfp.uga.edu/faqs/general-canning/category/faq-canning
https://extension.psu.edu/when-a-jar-becomes-unsealed
well said Anna, I am professional chef and canner, I watched my mum can or bottle as we called it for many years. she explained, all the dangers 40 years ago, as a farmer’s wife who never attended school. I was always impressed with her practical hands-on generational knowledge. I read some other post and recipes and are surprised not more people actually die. Thank you for your kind and diligent and practical advice.
Good article and helpful comments. It doesn’t hurt to remind even an old canner like me. I’ve been canning for over 60 years.
My son has 5 green houses grow many many veggies for market then what is left brings to me and I can. I was taught by my mother in law years ago. Now I am trying to remember all her rules. So my question is I use a pressure cooker and not sure how to use. Direction that came with it don’t really tell me much. So I get my pressure up to 50 then let out a little pressure. I do this a few times until it back down to below 10. Then I turn off burner and let cool off. I do this with green beans, potatoes, carrots and beets. Is this safe or wrong?
Hi Lorraine,
Unfortunately, pressure cookers and pressure canners are not the same thing. Pressure cookers are not approved as safe for pressure canning.
The absolute best resource for anything to do for canning is the National Center for Home Food Preservation. Check out this link for all of the information you could need: https://nchfp.uga.edu/#gsc.tab=0
Best of luck! -Ashley (Assistant)
There is no need to “sterilize” jars, lids, and bands. All you need to do is wash them with hot, soapy water as you would any other dishes. You are going to use them in canning, which is specifically for killing bacteria, so the canning process WILL kill any icky things you think sterilizing will kill.
Also, the photo shows canned food in jars with the rings still on. The article makes no mention of taking the rings off after the jars have sealed and a day or so has passed. You NEVER store the jars with the rings on. It can create a false seal, and THAT can lead to making you sick! That should have been rule #1 in the article. I see so many, many photos on Pinterest of home canned food in jars with the rings still on. That is one of the very first rules I learned when learning to can!
The article is about botulism, and leaving the rings on has no effect on whether or not canned food may carry a risk of botulism. In fact, the reason you should remove bands/rings is so that you can tell if one of your jars didn’t actually seal. If you leave the rings on and the lid didn’t actually seal, it could create a false seal and your food could mold and spoil, resulting in food waste, so you’re not wrong there (and you’re correct, it was a poor choice of image to use on a canning post, although I admit I don’t always remove the bands and have never had a jar not seal). However botulism comes from jars of food that have been sealed well. It thrives in anaerobic (low/no oxygen) environments, like the type of environment inside a sealed canning jar. The key to avoiding botulism in home canning is to always acidify or pressure can low acid foods according to the directions.
As for sterilizing jars, you do not need to sterilize them if you’re pressure canning, but you do need to sterilize them if you’re water bath canning certain foods, or at the very least they should be kept in a simmering hot water bath until ready to be filled.. This is according to the National Center For Home Food Preservation and the Ball Complete Book Of Home Preserving, which are both trusted sources for home canning information. Better safe than sorry! After all, had I not mentioned sterilizing jars, someone probably would have left a comment calling me out for that;)
This is a great tidbit of information. I am new to canning and wondered why we are told to take the rings off when the jars look much nicer with them on!
A great common sense post, Anna! I am not a canner. I had hoped to try my hand at water bath canning tomatoes this year, but my garden didn’t cooperate. (And I am still scared to death of pressure canning, figured if I could successfuly water bath can, it would build my confidence) I’ve done a lot of my own research, and talked with friends who can regularly. Your article sums everthing up very succinctly regarding canning safety.