Botulism in fermented foods. Is it real? We in the Western world live in an undeniably germophobic culture. Everyone knows that bacteria are bad, right? So it’s no wonder that there’s some skepticism about fermented foods–I mean, you let bacteria grow on purpose?
The question of safety in terms of fermented food is not a new one. I’m a microbiologist, and I’m constantly teaching my students (most of whom will become nurses) about the dangerous bacteria that cause all kinds of disease, so I decided to turn my skills to fermented foods. How often do people get botulism? Are Salmonella and E. coli things to be concerned about? What about mold?
Is There a Risk of Botulism in Fermented Foods?
The biggest specter of food safety is definitely botulism, and for good reason. In fact, botulism is such a big deal, I decided to focus only on this disease in this article.
The bacterium known as Clostridium botulinum produces a toxin–known as botulism (or botulinum) toxin–that is the most toxic substance ever discovered or made. THE MOST TOXIC. Nothing that humans know about is more toxic–it’s estimated that 1 teaspoonful of the pure toxin could kill the entire city of San Francisco. (So of course we humans decided to purify it and inject it in our faces…amazing!) This bacterium has another amazing property: it makes spores that can survive really hot temperatures–even boiling! It also grows anaerobically (without oxygen), so you might start to wonder why it’s not a problem in ferments.
Botulism IS a big concern when canning foods. In a jar of–for example–canned pumpkin, boiling the jar in a boiling water bath will kill off most of the bacteria, except those like C. botulinum that have heat-resistant spores. And the inside of the jar has no oxygen! Perfect conditions for botulism.
And what about botulism in fermented foods? However, this seeming superbug has its Kryptonite. Acid is the primary one. And what do almost all fermentation reactions produce? Acid, of course! Our good friends, the lactic acid bacteria (LAB), produce lots of lactic acid, as well as acetic acid and formic acid. These acids, when they build up enough to bring the pH below 4.6 (lower is more acidic), will prevent C. botulinum from growing, even if the spores are present.
Many LAB also produce antibacterial substances known as bacteriocins. Many of these can target C. botulinum as it grows, causing it to die. I know it may seem weird that bacteria produce antibacterial substances, but the LAB are resistant to them (if they weren’t, they obviously wouldn’t survive very long making them!) This means that the simple presence of the LAB bacteria may prevent botulism in your food, even if the pH didn’t quite get as low as it should. Some food scientists are even considering using specific LAB as natural food preservatives!
So, this sounds good in theory. How does it work in real life? Well, the good news is that foodborne botulism is actually not that common in the US anymore. The CDC (Centers for Disease Control and Prevention) monitors botulism, and tracks it down to its source. Their last twelve annual reports (2001 – 2011) show an average of 18 cases of foodborne botulism in the US per year. Almost all of these could be linked to either improperly canned foods (see above), “Alaskan native foods” (various meats), or bootleg prison alcohol. One instance of fermented tofu, and one instance of fermented fish heads were the only fermented foods listed.
Safe and Healthy Food
Notice that sauerkraut, kim chi, yogurt, kefir, kombucha, etc… were not listed anywhere. The CDC says on their website that because they monitor the antitoxin, “nearly all recognized cases of botulism are reported,” so it’s not like there are a bunch of hidden cases of sauerkraut botulism out there. And, of the two cases of fermented foods showing up on the list, they are both high-protein, low-sugar foods, which makes it hard for the LAB to grow and ferment. And two cases in twelve years? With all of the people in the US? I’m not surprised that somebody, somewhere made a mistake with something like fish heads, and didn’t set up the fermentation correctly.
Now, it is possible to safely ferment meats and other high protein foods, but they do take more caution than vegetables, and I don’t cover fermented meats on this site. The foods I do cover all contain some easily fermentable carbohydrates, allowing the LAB to thrive and keep C. botulinum at bay. I believe it’s safe to say that fermented vegetables, grains, dairy, sugar water and fruits will never give you botulism in fermented foods.
So go ahead, start your ferments and get your probiotics! Even a beginner won’t have to worry about this bad bug.