“On a scale of one to botulism, how concerned should I be about the months-old garlic confit sitting in my pantry?”
It hadn’t even been five minutes into my conversation with Cathy Barrow, longtime Food52 contributor and author of the canning cookbook, Mrs. Wheelbarrow’s Practical Pantry, before I hijacked the interview to address the five-month-old ingredient my boyfriend was heading home to cook dinner with.
“I would say it has potential for making you sick,” Cathy said, diplomatically. I texted my boyfriend to abandon the Aglio e Olio—and find a hazmat suit.
Okay, so I may have overreacted, but it’s easy to get nervous after reading the C.D.C.’s definition of botulism, an affliction best known for being transmitted through improperly canned foods.
“Botulism is a rare but serious paralytic illness caused by a nerve toxin that is produced by the bacterium Clostridium botulinum.”
Foodborne botulism is most frequently caused by the ingestion of canned and preserved foods when the bacterium Clostridium botulinum is present, and can be fatal by way of muscle paralysis. Not to mention that the bacteria has no scent or appearance. (Like I said, scary.)
But, as Cathy pointed out to me, botulism is also extremely rare. According to the C.D.C.’s website there are 145 cases of botulism reported in the United States each year (you may recall 2015’s church potluck disaster, which afflicted 28 people and killed one). And of those 145 cases, only 15% are foodborne and only 3 to 5% fatal (down from botulism's 50% fatality rate in the past fifty years), due to advancements in treatment and awareness.
That’s roughly four people who die of botulism per year—less than vending machines, which kill three times as many people annually. (If a vending machine is tipping over, get out of its way).
As Cathy put it, joking, "If you want to kill your family, there are better ways to do it."
Still, as with any food safety concern, avoiding botulism requires diligence. But as Harold McGee, author of the blog Curious Cook and food chemistry expert, wrote to me, “Fear doesn't belong in the kitchen. Prudence and caution do, developed from a basic understanding of how disease microbes behave and can be controlled.”
So how does a reasonable home cook prevent it?
Here are 4 things to keep in mind to give due caution and diligence to botulism:
1. A fear of botulism should never keep you from canning.
Cathy, who cans everything from rhubarb chutney, to peach pie filling, and tomatoes (did we mention, she's written a book on it?), has never met anyone who's suffered from botulism. It's not that botulism isn't out there, but when all of the precautions are taken, canning is a safe and wonderful way to preserve your favorite foods year-round. As Cathy puts it, “Follow the rules, be smart, and stop worrying so much.”
2. Some foods are more likely to host the botulism-causing bacterium than others.
The bacterium that causes foodborne botulism, Clostridium botulinum, is unique in that it thrives in anaerobic (airless) conditions—specifically, it prefers an environment that’s low in salt, sugar, and acid at room temperature. This is what Cathy refers to as the “perfect storm situation.”
In other words, low-acidic vegetables (a pH level lower than 7; or lower than 4.6 to be considered “extremely low-acidic”) like tomatoes, green beans, corn, beets, and garlic and most foods that grow underground are more likely to provide a happy home for botulism-causing bacteria.
“When people tell me, I just canned my grandmother’s special sauce—with onions and peppers, which are two things that are extremely low in acidity—it’s like they’ve created a botulism stew,” Cathy says, “They’re better off canning the peppers and tomatoes separately, then making the sauce later.” The more acidic vegetables in one place, the more likely it is for the bacterium to be able to survive.
It’s also important to keep in mind that meat and fish have low pH levels as well—so in places like Alaska where fermented seafood is common, the same precautions that are taken for low-acidic foods should be observed. Here’s a helpful guide for the pH levels of food, from the C.D.C.
On the other side of things, even though fruits with low pH levels like raspberries and blueberries are often used for jams, the high sugar content of jams and fruit preserves serves as a deterrent for botulism. “If you have jam in your fridge for 15 years,” Cathy said, “the worst thing you’re going to get is mold on your jam.” She also said that vinegar-pickled vegetables are also not likely to develop the botulism bacterium. Because pickled vegetables are covered in an acidified brine, the process creates a high enough acidity to prevent the risk of botulism.
3. Boiling alone does not kill botulism bacteria (and neither does cooking).
The reason Clostridium botulinum is so hard to kill is because it creates heat-resistant endospores, or a dormant spore that the bacterium can reduce itself into for survival (!). The botulism bacterium can exist in this dormant state for thousands of years, until it finds itself back in ideal conditions. In short, boiling the jar with the canned food inside won’t kill botulism: While water boils at 212° F, botulism bacterium only die at 241° F.
Pressure canning (not to be confused with a warm water bath or pressure cooking) is the only way to get the internal temperature of the canned food to 250° F, killing botulism. “Even if you put your can in a 350° F oven, you won’t be able to get the center of the jar cooked to a higher temperature,” Cathy said. Here’s a helpful guide to how long the can should be cooked in that temperature, by altitude, size, and contents.
Likewise, there’s no guarantee that even after you’ve opened your can and added its contents to a dish, that baking that dish will kill any strains of botulism. The only way to guard canned food against botulism is to pressure can it for the correct amount of time—period.
4. Once you’ve canned properly, there are still precautions to take.
Even after you’ve killed all botulism-causing bacteria at the time of canning, once you’ve opened that can to eat your preserves, the bacterium can still find a way into a can from other sources. Because of this, Cathy avoids keeping canned foods, once opened, like canned tomatoes or soup for more than three to four days, and only uses clean utensils to serve herself each time.
And you're still feeling a little hesitant about the whole pressure canning thing, there are plenty of things you can safely preserve with a simple boiling water bath. Here are a few of our favorites—from compotes to quick pickles and jam:
Canning essentials:
Do you have any questions about botulism? Are you a first-time canner? Tell us in the comments below!
