, , , , , ,

Every now and then you may hear about botulism. Most parents know that honey for a child under one is an absolute no-no, and although we might not be able to explain why, that’s because of botulism.

If you’ve been interested in home canning, you may have heard of botulism too. Or perhaps you saw a news blurb about someone who got botulism (probably from home canning), and is lucky to be alive now.

While home canning is amazing, it has to be done right, and more than one person has been turned off to trying it after hearing about botulism. Thankfully botulism isn’t too difficult to understand, which means that canning safely can be done with just a little care and knowledge. So let’s talk about botulism.

Botulism is the world’s deadliest toxin, produced by a spore in certain conditions. Specifically these certain conditions are oxygen-free, low-acid, and moist. Think about the conditions inside of a sealed jar of food and you understand why canning is one of the most common reasons for botulism poisoning for anyone over a year old in the US.

According to the CDC, botulism poisoning manifests in systems that will eventually lead to paralysis. This is not just a paraplegic sort of paralysis, as it can paralyze the respiratory system, thereby causing death. It can take time for the symptoms to manifest and progress, but they are a slow march towards death. Untreated, the death rate is 50% or higher. Treated with modern medicine, it’s as low as 3%, but will often require a breathing machine and medical care for months.

Botulism isn’t terribly common, and most cases of botulism–about 65% of the 145 cases a year–are infant botulism. This is because children under one tend to have low-acid stomachs compared to adults, so there isn’t sufficient acid to prevent the spore from producing its toxin. Some foods, like honey, are much more likely to carry the spore and should not be fed to infants until they are old enough for the digestive tract to be sufficiently acidic. About 20% of the cases are wound botulism, which is when the spore gets into a wound and starts secreting the toxin. Finally, 15% are foodborne, mostly from home canned foods. There are a couple other ways to get botulism poisoning, but they are quite rare.

Spores are hard to kill and can wait dormant for hundreds of years to finally “wake up” and start secreting the toxin, but thankfully this only happens in certain conditions, which home canners can easily control. There are two ways to prevent botulism in canning: acidity and heat.


Botulism spores can survive boiling (212F/100C), so water bath canning does not kill botulism spores.

However, food with a pH of 4.6 or less is considered high-acid, and the spore will not wake up and secrete toxins in an acidic environment. Commonly canned foods with a sufficiently low pH, or which can be modified with the use of an acid such as lemon juice or vinegar, include most fruits, berries, many tomato and salsa recipes, and pickled foods. This is why jams, preserves, and pickles can all be canned in a water bath.

Vegetables, meat, legumes, and dairy all have a more alkaline pH and cannot safely be canned in a water bath (with the exception of pickled vegetables).

In all cases, following approved methods and recipes is important to ensure acceptable acidity. Home canners generally don’t have the equipment to properly test the pH of their recipes to ensure safety. There is a certain amount of tweaking that can be done with recipes, such as in choosing which seasonings to use in tomato sauce, but it must always be within safe parameters that won’t raise the pH.


While botulism isn’t killed by boiling temperatures, raising the temperature sufficiently above boiling will. 240F is usually sufficient, although commercial guidelines in the US require 250F for three minutes. When raised to this temperature for a long enough time, the chances of a botulism spore surviving is about one in a trillion. Since there’s not nearly that many people in the world, that’s pretty good odds.

In order for a home canner to reach these temperatures, a pressure canner is required. This is not the same as a pressure cooker. Always follow official guidelines for processing. Home canners cannot be absolutely sure of how long it takes for all of the food through every can to get hot enough long enough, so it is essential to not skimp on processing times. It is also important to make sure that your pressure canner is functioning properly, which means that if your canner has a seal that could fail (rubber) it is important to check its condition, and dial gauges must be calibrated before canning.

My dream pressure canner, which I plan on getting before my garden starts producing enough abundance to can vegetables or other low-acid foods in the next few years, is an All American Pressure Canner as it relies on neither of these. The seal is metal-on-metal and it uses a weighted gauge which cannot fail so long as the canner is functional, so the dial gauge is for reference only and the canner can still be used safely if the dial is incorrect.

Of Note

Hygienic canning methods in general also reduce the risk of botulism poisoning, as cleanly processed food has less chance of having spores introduced into them in the first place. This means things like washing hands before the process and at any point during which might require it — such as after using the bathroom or handling something that isn’t clean — sterilizing jars, lids, and rings at the beginning, using a clean canner and equipment, and not using any questionable food.

As noted twice above, following official, approved recipes and processing methods is extremely important.


If all that seems intimidating to you, let me make this really simple.

Follow all the steps, be clean, and use official tested recipes and methods.

That’s really all you need to know for safely canning food at home. Really.

So if you’ve been terrified of poisoning your family and it’s kept you from canning those lovely peaches or berries you see sold in bulk every summer, just go get the Ball Guide to Preserving, a water bath canner and canning tools, and do what it says.

And if you know that someone does not follow the guidelines, please politely decline eating their preserves. Although you’d probably be okay, you don’t need to risk being stuck on a ventilator for months.