Botulism. Just the word is enough to put a terrified expression on the faces of participants in my food preservation workshops, and with good reason. But armed with some facts about this scary bacterium, you will never have to worry about it when you're canning food at home.
How dangerous is botulism? Very. You can't see it, smell it, or taste it, and just one teaspoon of the botulism toxin that is produced by Clostridium botulinum would be enough to kill hundreds of thousands of people.
Fortunately, there are some very simple ways to make absolutely certain that botulism is a non-issue in your home-canned foods.
As far as canning methods go, you need to remember that non-acidic foods must be processed in a pressure canner, not a boiling water bath. That will make sense once you know the "why" behind the "what."
Although a brisk boil destroys botulism bacteria and toxins, it is not hot enough to destroy the spores. Now if you're going to eat the just-boiled food right away, that's okay. But if those spores are going to sit in a jar of incorrectly canned food on a shelf at room temperature, that could be a deadly problem.
What do I mean by "incorrectly canned"? I mean that something that should have been pressure canned was processed in a boiling water bath instead. The reason that is so important is that a pressure canner heats the food to hotter than the temperature of boiling water. It gets the food all the way up to 240F/116C, which is hot enough to kill botulism spores.
Here's why canning non-acidic foods in a boiling water bath is dangerous: The processing temperature in a boiling water bath cannot get hotter than 212F/100C, the temperature of boiling water at sea level. So the bacteria are destroyed, but not the spores that can grow into more bacteria.
Clostridium botulinum spores grow in an environment that has no air, is a temperature between 70F/21C and 110F/43C, and includes more than 35 percent moisture. Sound familiar? That's right - it's exactly the environment inside a canning jar of food stored in a kitchen cabinet at room temperature.
But the good news for home canners is that botulism is wiped out by food that has an acidic pH. That translates into the happy fact that you can safely process pickled vegetables, sugar preserves, and fruits in a boiling water bath (which you can do with a regular stock pot).
Temperatures below freezing as well as moisture levels below 35 percent also render botulism inactive, which is why it isn't a concern with frozen and dehydrated foods.
To sum up:
- Vegetables that are not pickled, soup stocks including vegetable stocks, and all animal products must be canned in a pressure canner.
- Acidic pickled veggies, jams, jellies, chutneys and fruits can be processed in a boiling water bath. Tomatoes may also be processed in a boiling water bath if you add a little acid in the form of vinegar, lemon juice, or citric acid.
- Frozen and dehydrated foods are safe from active botulism bacteria and spores.