Paige Weisskirch, UC Master Food Preserver Online Program Volunteer

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“How Death Came, Unbidden, to Mrs. Sales Dinner Party”, an illustration accompanying an article reporting on a botulism outbreak due to improperly processed olives in The Philadelphia Inquirer, Nov. 30, 1919. 

Botulism Is Rare Because We Do It Right

UC Master Food Preservers get asked all the time whether botulism is really a risk. The internet is overflowing with posts championing unsafe practices, often relying on survivor bias and tradition. "My grandmother did it this way for fifty years and nobody died" and "I've been doing this for years and I'm still here" are common refrains.

The numbers can feel reassuring. U.S. surveillance summaries show that foodborne botulism is uncommon, with a median of 19 laboratory-confirmed cases per year from 2001–2017 (Lúquez et al., 2021). The key detail is why the totals are low. They are low because safe, science-based methods work. The threat is not imaginary or overstated. It is controlled by good practice.

Botulism remains a high-stakes hazard. In that same period, deaths were reported in 17 cases, a case fatality ratio of about 5 percent even with modern medical care (Lúquez et al., 2021). Public health guidance emphasizes that you cannot reliably detect the toxin by sight, smell, or taste, which is why prevention matters (Centers for Disease Control and Prevention [CDC], 2024).

What botulism is and what happens during infection

Clostridium botulinum is a bacterium that exists naturally in soil and aquatic environments worldwide (U.S. Department of Agriculture, Food Safety and Inspection Service [USDA FSIS], n.d.). Like many bacteria, it forms spores, which are dormant, protective structures that can survive harsh conditions for long periods. The spores themselves are not harmful, but when they encounter the right environment (low oxygen, low acid, adequate moisture, and suitable temperature in the case of C. botulinum), they germinate and the active bacteria produce botulinum toxin.

Botulinum toxin, also called botulinum neurotoxin, is one of the most potent poisons known (USDA FSIS, n.d.). It is the toxin, not the bacterium itself, that causes illness. Botulism is the name of the disease that results when a person ingests food containing this toxin or is exposed to the toxin via other routes.

What happens during infection

Symptoms typically appear within 12 to 36 hours after consuming contaminated food and begin with fatigue, weakness, blurred vision, dry mouth, and difficulty swallowing or speaking (Rao et al., 2021; World Health Organization [WHO], 2023). The toxin attacks the nervous system and causes descending paralysis that progresses from cranial nerve problems, such as drooping eyelids and slurred speech, to weakness in the neck and arms, and eventually to paralysis of the respiratory muscles (WHO, 2023).

The most life-threatening complication is respiratory failure. Botulinum toxin blocks the release of the neurotransmitter acetylcholine at nerve endings, preventing muscles from contracting (Rao et al., 2021). When this affects breathing muscles, mechanical ventilation becomes necessary, sometimes for weeks or months while the body slowly forms new neuromuscular connections (CDC, 2024; WHO, 2023). Intensive medical care during this time is essential to prevent complications such as pneumonia, blood clots, and infections.

Treatment of the disease centers on botulism antitoxin, which binds to toxin molecules in the bloodstream before they attach to nerve endings (Rao et al., 2021). The antitoxin can stop the progression of paralysis but cannot reverse damage already done. The most effective window for treatment is within the first 24 hours of symptom onset (Rao et al., 2021). Even with antitoxin and intensive care, some people still die from respiratory failure or secondary complications such as pneumonia or sepsis (CDC, 2024; WHO, 2023). The case fatality rate has improved from 40–50 percent historically to about 5 percent today, but that still represents real lives lost to a preventable illness (Lúquez et al., 2021; WHO, 2023). What makes botulism uniquely dangerous is that contaminated food may look, smell, and taste normal (CDC, 2024).

Why the numbers are low

Low case counts mean prevention works. Safe canning is an entire system: selecting quality food, preparing it according to tested recipes, choosing the correct jar size, using the right processing method for the food's acidity, applying the right pressure or temperature for altitude, processing for the correct time, cooling properly, checking seals, and storing jars appropriately (Missouri Extension, 2015; National Center for Home Food Preservation [NCHFP], n.d.-a; U.S. Department of Agriculture [USDA], 2015). The process heats food to destroy microorganisms, drives out air, and creates a vacuum seal that prevents recontamination (Missouri Extension, 2015; NCHFP, n.d.-a). When followed as a complete system, botulism remains rare.

The success of these safeguards can create a dangerous illusion that shortcuts are harmless, especially when personal experience is offered as "proof" a method is safe. The cases we do not hear about, jars quietly discarded because they looked or smelled off, or illnesses never connected back to a specific jar, do not make it into those reassuring anecdotes.

Why boiling water is not enough for low-acid foods

A persistent misconception is that boiling low-acid foods, such as meat or vegetables, long enough will destroy C. botulinum spores without pressure canning. The limitation is temperature. Water boils at 212°F at sea level, and at lower temperatures at higher elevations. That temperature is not high enough to destroy spores in low-acid foods within a reasonable processing time (USDA, 2015; NCHFP, n.d.-a). The NCHFP notes that the time needed to inactivate C. botulinum spores at 212°F would range from 7 to 11 hours, an impractical amount of time that would result in mushy, unpalatable food (NCHFP, n.d.-a). "Just boil it longer" is not a safety plan.

Pressure canning solves the temperature problem by raising the processing temperature. under by increasing the pressure and thereby increasing the temperature at which water boils. For low-acid foods, validated processing procedures rely on the use of pressure canning (USDA, 2015; NCHFP, n.d.-a).

Boiling does have an important role after opening the jar. The CDC recommends boiling low-acid, home-canned foods for 10 minutes at altitudes below 1,000 feet, adding 1 minute for each additional 1,000 feet (CDC, 2024), before consuming them. This destroys toxin but not the spores and does not "rescue" an improperly canned jar. If you suspect improper canning or see signs of spoilage, discard the jar without tasting (CDC, 2024).

Dry canning is not canning

"Dry canning," whether heating jars of dry goods in an oven or "pressure canning" vegetables without adding the recommended amount of liquid, does not create the conditions needed to reliably control C. botulinum spores. The entire interior of each canning jar must reach the target processing temperature and stay at that temperature long enough to destroy the spores. Heat is transferred more slowly in jars that don’t contain liquid than it is in jars with liquid. In addition, bacteria and their spores are killed more quickly by “wet heat” than “dry heat.”. The liquid specified in tested canning methods is not optional; it supports predictable heat penetration and kill rates, which are what tested processing times are based on (Ingham, 2020; NCHFP, 2020; Penn State Extension, 2024).

Recent outbreaks in multiple countries

Botulism is rare but not unknown. Recent outbreaks show the same pattern: the risk follows behavior, not geography.

In the United States, a 2024 outbreak in Fresno County, California linked to home-prepared prickly pear cactus (nopales) sickened eight people. Six required ICU care and two needed mechanical ventilation (Vohra et al., 2025). In Italy, outbreaks from commercially prepared foods resulted in hospitalizations and deaths, including a Diamante, Calabria cluster where at least 18 people were exposed after eating sandwiches from a food truck; four of them died (Euronews, 2025). In France, six people developed severe symptoms after sharing a meal that included carrot cake. The 78-year-old woman who made the cake later died, and French media linked it to a jar of home-canned carrots (Food Safety News, 2025).

These examples matter because they negate a common argument: that using a group or place as "proof" that safety guidance can be ignored. "In Europe they do not pressure can" or "The Amish do it this way" are still anecdotal evidence. They do not validate methods or change the microbiology. French public health information explicitly notes that boiling is insufficient to sterilize foods because botulinum spores resist boiling water (Santé.fr, 2023). The same science applies everywhere. The only thing that changes risk is whether the method reliably controls conditions that allow toxin to form.

Bottom line

Botulism warnings are not hype. They help prevent a rare but severe hazard. The reason more people do not get sick is that safe practices work.

Clostridium botulinum does not respond to internet trends, personal anecdotes, or confidence. It responds to conditions: temperature, acidity, time, and oxygen availability. The science of what causes botulism and what prevents it is well established. When spores find an environment with low oxygen, low acid, adequate moisture, and the right temperature, they germinate and the resulting bacteria produce toxin. When one or more of those conditions is reliably controlled, such as using boiling water canning only for high-acid products, the risk is eliminated.

Many people who follow unsafe methods learned them from trusted sources and share their food with sincere care and good intentions. The disconnect happens when personal experience is offered as evidence of safety. One person's uneventful history with a method does not make that method safe. It means the person has been fortunate. Validation comes from controlled testing that shows whether a method reliably prevents toxin formation across different conditions, foods, jar sizes, and altitudes. That is what tested recipes and processes provide, and that is what personal experience cannot replace.

The highest confidence comes from understanding the process you are following and knowing it has been validated. Science-based canning guidelines are the pathway to food that is both safe and shelf-stable, designed so home canners can preserve food with certainty rather than luck. The UC Master Food Preserver Program and University Extension offices exist to help people do exactly that, to preserve food safely through education grounded in research and tested methods. Safe canning practices protect not just the food, but the people who will eat it.

References

Centers for Disease Control and Prevention. (2024, April 25). Home-canned foods: Botulism prevention. https://www.cdc.gov/botulism/prevention/home-canned-foods.html

Centers for Disease Control and Prevention. (2024, June 12). Treatment of botulism. https://www.cdc.gov/botulism/treatment/index.html

Euronews. (2025, August 20). Death toll rises to 4 in botulism outbreak in Italy. https://www.euronews.com/health/2025/08/20/death-toll-rises-to-4-in-botulism-outbreak-in-italy

Food Safety News. (2025, August 4). Woman dies in French botulism outbreak. https://www.foodsafetynews.com/2025/08/woman-dies-in-french-botulism-outbreak/

Ingham, B. H. (2020, June 18). Unsafe canning practice: "Dry canning" vegetables. University of Wisconsin–Madison Division of Extension. https://florence.extension.wisc.edu/2020/07/07/unsafe-canning-practice-dry-canning-vegetables/

Lúquez, C., Edwards, L., Griffin, C., & Sobel, J. (2021). Foodborne botulism outbreaks in the United States, 2001–2017. Frontiers in Microbiology, 12, 713101. https://doi.org/10.3389/fmicb.2021.713101

Missouri Extension. (2015). Safe home canning basics (Publication No. GH1451). University of Missouri. https://extension.missouri.edu/publications/gh1451

National Center for Home Food Preservation. (2020, June 25). Dry canning raw vegetables is an unsafe practice. https://preservingfoodathome.com/2020/06/25/dry-canning-raw-vegetables-is-an-unsafe-practice/

National Center for Home Food Preservation. (n.d.-a). Ensuring safe canned foods. https://nchfp.uga.edu/how/can/general-information/ensuring-safe-canned-foods/

Penn State Extension. (2024, September 17). "Dry canning" is not recommended. https://extension.psu.edu/dry-canning-is-not-recommended

Rao, A. K., Sobel, J., Chatham-Stephens, K., & Luquez, C. (2021). Clinical guidelines for diagnosis and treatment of botulism, 2021. MMWR Recommendations and Reports, 70(2), 1–30. https://doi.org/10.15585/mmwr.rr7002a1

Santé.fr. (2023, October 26). Le botulisme : de quoi s'agit-il et comment s'en prémunir ? https://www.sante.fr/le-botulisme-de-quoi-sagit-il-et-comment-sen-premunir

U.S. Department of Agriculture. (2015). Complete guide to home canning (Agriculture Information Bulletin No. 539, Rev. 2015). National Institute of Food and Agriculture. https://www.nal.usda.gov/exhibits/ipd/canning/items/show/101

U.S. Department of Agriculture, Food Safety and Inspection Service. (n.d.). Clostridium botulinum and botulism. https://www.fsis.usda.gov/food-safety/foodborne-illness-and-disease/illnesses-and-pathogens/botulism

Vohra, R., Barash, J. R., Karmarkar, E. N., Koch-Kumar, S., Sanchez, N., Gore, M., Michel, K., Rangel, M., Armstrong, E., Pimentel, L., Kraushaar, V., Kimura, A., Stainken, C., Nat, A., Nat, R. S., Cherukupalli, S., Schneider, D., Vugia, D. J., Solis, T., … Al Saghbini, S. (2025). Foodborne botulism outbreak after consumption of home-prepared cactus (nopales), Fresno County, California, June 2024. MMWR Morbidity and Mortality Weekly Report, 74(24), 408–413. https://www.cdc.gov/mmwr/volumes/74/wr/mm7424a1.htm

World Health Organization. (2023, September 25). Botulism. https://www.who.int/news-room/fact-sheets/detail/botulism

Marina Hsieh and Henry Shaw, UC Master Food Preserver Online Program Volunteer

Known as Mứt Tắc in Vietnam, these delicious, candied tidbits are a traditional Lunar New Year treat. Just as you eat fresh kumquats whole, you candy all parts of the fruit, whether whole, sliced, or quartered. Serve with tea, in fancy drink concoctions, as a garnish to cakes and desserts, or with salads and savory dishes. 

Yield: about 30 candies or 1 pint in syrup

Ingredients:

• 1 pound kumquats
• Water
• 2 cups sugar

Optional spices:

• 1 (1-inch) coin ginger
• 1 cinnamon stick
• 1 star anise pod

• 2 cloves

   

Instructions:

1. Using a bird's beak knife or other sharp paring knife, cut 6 to 8 vertical slits around each kumquat, spacing them evenly. Leave the top and bottom ends of each kumquat intact and be careful not to cut all the way through the fruit (Image 1).
2. Lightly pinch the top and bottom of each kumquat to form a lantern shape. Use a toothpick or knife tip to gently remove the seeds. Don't worry if you can't remove every seed; they will loosen during cooking, and it's more important to handle the kumquats gently so they don't split apart.
3. Fill a saucepan with water and bring to a boil. Add the kumquats and blanch for 1 minute. Remove the kumquats and drain. Repeat this process two more times (three times total), using fresh water each time. Check again for stray seeds and gently remove them.
4. Refill the pot with 2 cups of water, sugar, and spices (if using). Bring to a boil, stirring to dissolve the sugar. Add the kumquats and reduce heat to low. Keep the kumquats evenly covered in syrup by periodically spooning syrup over them or gently submerging them with a wooden spoon; they will initially float. Simmer until the peel is translucent, about 45 minutes.
5. Remove from heat, cover the saucepan with a cloth, and let the kumquats steep for 8 hours or overnight.
6. At this point, one can dry the kumquats to make candy or store them in syrup. 

Image 1. Slicing and deseeding in preparation for making candied kumquat flowers (Used with permission, Henry Shaw). 

Dried:

1. Using a slotted spoon, remove each kumquat from the syrup and gently press down on the top and bottom to flatten it into a flower shape. This is also a good opportunity to press out any remaining seeds.
2. Dry the kumquats on a baking rack, on a parchment-lined baking sheet in an oven at 200°F or below, or in a dehydrator at 135°F. Drying time depends on the method, conditions, and fruit size; in a dehydrator it takes about 8-12 hours.
3. The candies are ready when they are pliable and no longer very sticky to the touch. They may be optionally rolled in sugar like any candied citrus peel or sprinkled with a few flakes of Maldon salt just before serving.
4. Store in an airtight container in the refrigerator. Kumquats are best consumed within a week, but properly dried and stored, they can keep for months. 

In Syrup:

1. Transfer the kumquats to an airtight container, cover with syrup, and refrigerate (Image 2). Kumquats in syrup are best consumed within several weeks.

Note: Strain and store any remaining syrup in a clean, preferably sterilized, jar in the refrigerator. Use it to flavor sparkling water and cocktails, drizzle on cake or ice cream, or mix into dressings and marinades. 

Candied kumquat flowers (Used with permission, Henry Shaw).

Recipe source: Adapted from Emily Han, 2013, UCCE Master Food Preserver Program of Amador/Calaveras Counties

Joy Agcongay, UC Master Food Preserver Online Program Volunteer

Why Salt and Sugar Matter in Preserved Foods

When we talk about salt and sugar in general cooking, we often think of them as tools to enhance flavor. In food preservation, however, salt and sugar often play a different role. They help control microbial growth by reducing the amount of available moisture in foods. This is why they are key ingredients in many shelf-stable products such as jams, jellies, and pickled vegetables.

Historically, salt- and sugar-based preservation methods were developed to support long-term food storage for households and communities, and not designed to address the dietary needs of babies and toddlers, who were typically fed breast milk and foods prepared for near-term use.

Because salt and sugar play a key role in creating shelf-stable conditions, changes to their use directly affect how foods can be safely preserved.

Why Baby and Toddler Foods Are Different

Research-based nutrition recommendations for young children, particularly those under the age of two, emphasize limiting sodium (i.e., salt) and avoiding added sugars and sweeteners, including honey. Current guidance from the UC Nutrition Policy Institute reflects these recommendations for infant and toddler feeding.

When salt and sugars are reduced or omitted, foods no longer have the same conditions that support long-term, shelf-stable preservation. This difference directly affects how baby and toddler foods can be safely stored and preserved at home.

How Texture and Moisture Affect Storage

Many foods made for babies and toddlers are soft in texture—puréed, mashed (Image 1), or finely chopped. These textures share characteristics that affect storage and preservation.

Foods for small children are: 

• often higher in moisture
• more uniform
• dense in texture, and
• prepared without added salt or sugar

These characteristics influence which preservation approaches are appropriate and help explain why guidance for baby and toddler foods differs from that for many other home-preserved foods.

Image 1. Mashed butternut squash and rice baby food (Used with permission, Paige Weisskirch). 

Why Commercial and Homemade Baby Foods Differ

These differences often raise questions when caregivers compare homemade baby foods to products found on grocery store shelves. Commercial baby foods are often shelf stable because they are processed and packaged using specialized equipment and tightly controlled conditions that are not available in-home kitchens. Because of these differences, research-based home food preservation guidelines follow different rules. Most homemade baby and toddler foods—again, typically prepared with limited salt, no added sugars or sweeteners, and soft textures—are not suitable for shelf-stable preservation at home.

For home-prepared baby and toddler foods, the safest approach is careful preparation followed by long-term storage in the freezer, while following current nutritional guidance for salt and sugar. 

With the right preparation and storage choices, homemade baby and toddler foods can be both safe and practical at home.

Cole Imperi, UC Master Food Preserver Online Program Volunteer

County of residence: Los Angeles

Cole Imperi and fellow trainees (Used with permission). 

The first time I canned anything was the second summer after I bought my first house a few blocks from the Ohio River in Northern Kentucky. I had set up a big backyard garden comprised entirely of heirloom tomatoes, and discovered what happens at the end of a prolific growing season—pounds and pounds of tomatoes that need to be brought inside and dealt with before the first frost.

My husband and I learned to can out of necessity, and we started with tomato jam. If I remember correctly, we made 48 half pints that first season. 

The second thing I ever canned was pickled peaches. My neighbor that lived caddywhompus to us had two peach trees. Exasperated, he showed up at my back fence and dropped two big black garbage bags full of peaches into my backyard and said DO SOMETHING WITH THESE. They became pickled peaches. 

But I didn’t come to the Master Food Preserver (MFP) program because of canning, I came because of grief. But not in the way you might think!

In my career, I’m a thanatologist. Thanatology is the study of death, dying, grief, and loss. In all my years doing this work, I’ve noticed that grievers (and those who love them) tend to congregate around places where transformation happens. Gardens and kitchens are places of transformation. Gardeners turn soil and seeds into harvests, and cooks turn ingredients and spices into meals. The products of gardens and kitchens become tangible reminders that people love us, and that we love them. Casseroles dropped off on doorsteps, or a flat of tomatoes left by a neighbor at your back door, or a half pint of fig preserves left on your desk at work… just because. Food is often a container for things that are hard to say with words alone. And grievers? They use grief to turn their losses into healing, into discovering their ‘new normal’, into whatever comes next.

In early December of 2025, my husband and I packed up two big boxes to send to each of our parents who live across the country. Each box contained 7 different things I’d canned since finishing the Master Food Preserver training program in June of 2025. We were really packing up boxes of food that said, “I miss you” and “I miss sharing meals with you.” 

The other draw for me is community. I’ve been a volunteer and an educator the bulk of my adult life. And part of why I value those things so much is absolutely informed by my work as a thanatologist—when loss shows up, you really see who you can count on, who shows up, and who doesn’t. For someone who’s a transplant to Los Angeles, it’s important to me to give back to a community that has embraced and welcomed me and helped me find a sense of ‘home’ here, too. 

There’s also a part of food preservation that hits home for a lot of people, but in a legacy sort of way. When my fellow Master Food Preservers offer classes to the public, one of the most common questions we get are from attendees who say something like: “My Grandma used to can, can I use her recipes?” For a lot of people, canning and food preservation in general touch on memories, on growing up, on the relationship we still have to our loved ones, even if they’ve passed on. (And by the way, the answer to that common question is “probably not”. You can still can tomatoes (or whatever it was that Grandma did), it’s just that we know a lot more about food safety these days, so the recipe might be tweaked, but it will also probably taste better. Safe, tested recipes mean they are tested not only for safety, but also for flavor and texture.) A lot of people are discovering or reconnecting to their roots when they sign up to take one of our food preservation classes. 

The MFP program was exceptionally rigorous, and it completely transformed my relationship to my kitchen. I’m a better cook just in general because of the program, and it made me a better gardener too. It’s rewarding to be able to contribute to my community in this way. I’d highly recommend this program to anyone who has even a tiny interest—we need more people from more backgrounds and experiences to join our crew. While I came to the program by way of thanatology, maybe you’ll find your way here because of your own unique background and experiences.  

Robin Martin, UC Master Food Preserver Online Program Volunteer

County of residence: Sacramento

Robin Martin (Used with permission).