Industry
What the documented botulism cases actually show
The surveillance record is the closest thing to case studies this subject has. What US and international data say about who gets sick and from what.
What to take away
- Home-preserved food, not commercial food, dominates the US record. In the lower 49 states a noncommercial item was implicated in 91 percent of events with a known food.
- Home-canned vegetables were the single most common implicated food in those events, at 44 percent.
- Alaska is a category of its own39 percent of US cases in the reviewed period, almost all from traditional fermented foods eaten without cooking.
- Practices matter more than intentions. A household survey in Georgia found specific canning habits associated with higher and lower risk.
The US surveillance picture
The CDC's Emerging Infectious Diseases review of foodborne botulism in the United States from 1990 to 2000 is the closest thing home preservers have to a body of case studies. Across those years there were 160 foodborne botulism events affecting 263 people, an annual incidence of 0.1 per million, with a case-fatality rate of 4 percent.
Conditions for Botulism Growth vs Inhibition
Growth and toxin
- Oxygen
- Anaerobic
- Salt
- Low salt
- Acid
- Low acid
- Temperature
- Ambient
- Heat
- Not heated
Inhibited by
- Oxygen
- Not anaerobic
- Salt
- High salt
- Acid
- pH below 4.5
- Temperature
- Below 4 C
- Heat
- Above 121 C
US Foodborne Botulism 1990-2000
- 160events
- 263people affected
- 0.1 per millionannual incidence
- 4%case-fatality rate
A particular food was implicated in 126 of the events. In the lower 49 states a noncommercial food item was implicated in 91 percent of those, most commonly home-canned vegetables at 44 percent. Two restaurant-associated outbreaks affected 25 people.
The same review sets out the conditions the organism needs and the ones that stop it. Growth and toxin production occur only in an anaerobic, low-salt, low-acid environment.
Growth is inhibited by refrigeration below 4 C, heating above 121 C, high water activity, or acidity below pH 4.5. Toxin is destroyed by heating to 85 C for at least 5 minutes.
Read that list next to the home directions and every rule here becomes legible. Salt, acid, temperature, and pressure are not arbitrary.
Why Alaska stands apart
Of the 263 cases, 103 were in Alaska, all attributable to traditional Alaska Native foods. Type E toxin caused 90 percent of Alaska cases. The foods involved include fermented fish and fish eggs, seal, beaver, and whale, fermented at ambient temperature and often eaten without cooking.
That is the pattern worth understanding rather than judging: ambient-temperature fermentation of low-acid, low-salt animal foods, eaten raw. It is the exact combination the organism needs.
What a household survey found
A population-based study of home canning practices in the Republic of Georgia surveyed 2,742 households to explain regional differences in botulism incidence. Home canning with a device that hermetically seals the lid was practiced by about 66 percent of households.
Several practices raised risk in high- versus low-incidence regions. Waiting six months or more between canning vegetables and eating them was one. Adding more than one tablespoon of salt per liter, vinegar, or greens at preparation was another.
Decreased risk included canning more than 57 jars yearly and covering or immersing vegetables in boiling water before or after placing them in the jar.
The study also notes that the traditional local method, using high concentrations of salt and vinegar without a sealing device, has not been associated with botulism cases, because it does not create the anaerobic conditions inside the jar.
The lesson in one table
| Finding | What it implies for a home kitchen |
|---|---|
| Home-canned vegetables lead the US record | Low-acid vegetables need a pressure canner |
| Ambient fermentation of animal foods drives Alaska cases | Temperature and acidity are the controls |
| Georgian botulism events centered on hermetically capped jars | A good seal on an under-processed jar is worse, not better |
| Boiling water treatment lowered risk | Heat steps in tested recipes are doing real work |
Our guide to what causes fermentation mistakes covers the everyday failures, and the starting point guide covers the process these numbers argue for.
Common questions
Is home preserving dangerous?
Are fermented vegetables the risk here?
Why is sealing not protective on its own?
Should I worry about restaurant food?
In this guide
- Why tasting is never a botulism safety test for home canned low-acid foodExplains why tasting is never a safety test for home canned food, what public health guidance says about botulism, boiling, and pressure canning low-acid foods.
- Home-canned meat and fresh fish: safety basics for kitchensPressure canning, a 10-minute boil before tasting, fish on ice within two hours: the meat and fish basics that keep a home or service kitchen safe.
- Serving home ferment dishes to guests without passing on the riskServing home-preserved food to other people: a guest cannot check your process, so the burden sits with you. What to serve, what to keep for yourself.
- Tomato Canning Jar Labels: What to Record and WhyHome ferment case studies labels: for tomatoes, record the tested recipe, the acidifier and amount, jar size, processing time, canner setting and altitude.
- Why we publish no home ferment case studies reviewsHome ferment case studies reviews: this site publishes none, because testing products takes buying, running, and repeating. Here is what to read instead.
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