Fermented Foods Safety and Home-Fermentation Risks
What the sources say about the safety of fermented foods, the documented risks of home fermentation including botulism, and who should be extra careful. No recipes or methods.
Content last updated . This page has not been medically reviewed.
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Short answer: properly made fermented foods have a long record of safe use, but they are not risk-free, and home fermentation adds risks that a kitchen cannot easily check. This page explains the risks. It gives no recipes or methods, on purpose.
Urgent signs. Foodborne botulism is a toxin illness. Symptoms include "double or blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth, and muscle weakness," and "all forms can be deadly and are medical emergencies." [1] If these appear after eating a home-preserved or home-fermented food, call 911 in the US. For poisoning questions, Poison Help is 1-800-222-1222 (US).
What the sources say about commercial and traditional ferments
- Usually safe when properly made. An expert panel wrote that, "when properly made from safe and wholesome ingredients, fermented foods are rarely associated with gastroenteritis." [2] A 2026 research-network summary described safety findings as "broadly reassuring in the populations studied, although reporting was inconsistent." [3]
- Some exceptions. The same panel said "some cheeses and low-acid fermented foods can pose a safety risk if the food is contaminated with Listeria monocytogenes" and other pathogens. [2]
- Uncontrolled fermentation. A 2022 review noted that for some products fermentation "occurs spontaneously, without the use of well-defined starter cultures, under poorly controlled or uncontrolled conditions," and that disease-causing bacteria including Listeria monocytogenes and Bacillus cereus have been detected in fermented foods. [4] The authors point to small-scale and household production as places where safety controls can be missing. [4]
- Salt, alcohol and amines. Salt (for example in soy sauce or kimchi) and alcohol are built into some fermented foods, [2] and bacteria can form histamine and tyramine; see Histamine, tyramine and fermented foods.
Home fermentation: documented risks
| Risk | What the source says | Strength of evidence |
|---|---|---|
| Botulism from fermented tofu | A 2006 California investigation of foodborne botulism in an older couple traced it to home-prepared fermented tofu and concluded the public "should be aware of the risk for botulism when preparing fermented tofu at home." [5] | Case report (public health investigation) |
| Acidity and salt matter for safety | The National Center for Home Food Preservation says a minimum, uniform level of acid is needed to prevent botulinum bacteria growth in pickled products, and that salt in fermented sauerkraut and brined pickles "is vital to safety and texture." [6] | Expert guidance |
| Using untested methods | The same center says to use only recipes with tested proportions of ingredients. [6] | Expert guidance |
| Pressure from sealed bottles | A tested home kombucha method from that center cautions that storing kombucha in airtight containers can build up carbon dioxide, "potentially leading to an explosion if not regularly monitored." [7] | Expert guidance |
| Kombucha and illness | A 2003 systematic review found no clinical studies of benefit and said case reports raised doubts about safety. [8] The review is from 2003, so it may not reflect today's products; we did not find a newer systematic review. | Case reports (low) |
If you ferment at home, use a tested, current method from a university extension service or the National Center for Home Food Preservation rather than a social media post. We do not provide methods here. MedlinePlus advises being very careful when canning foods at home, [1] and the expert panel names low-acid fermented foods as a contamination risk. [2]
Who should ask a clinician or be extra careful
- Pregnancy, age 65 and older, weakened immune system. Listeria infection is most likely to affect pregnant women and unborn babies, older adults and people with weak immune systems, according to MedlinePlus, and the FDA lists the same groups as high risk. [9] [10] Listeria can grow even at refrigerator temperatures. [10] Raw milk and raw milk products are on the avoid list. [9] See Foods in pregnancy and Raw sprouts, raw milk and undercooked foods.
- Severe illness or weakened immunity and live-culture foods. The risk of harm from probiotics is greater in these groups, per NCCIH. [11] See also Probiotic safety.
- MAOI medicines and histamine problems: see the histamine page linked above.
- High blood pressure, kidney disease or low-salt advice: salty ferments such as kimchi and soy sauce may matter; ask your clinician. See Kimchi.
- Proper evidence not found: we searched PubMed for home fermentation, botulism and Listeria in fermented foods and found no source comparing the safety of home-made and store-bought kefir or kimchi.
Related
Pasteurized vs unpasteurized foods, Food safety basics, Live cultures on labels and Kombucha.Frequently asked questions
Is it safe to ferment food at home?
It can be done safely with tested methods, but there are documented hazards, including a case of botulism from home-prepared fermented tofu. [5] We do not give methods.
What is the biggest danger of home fermentation?
Botulism is the most serious one named in the sources we read. It is rare but can be deadly. [1] Other pathogens such as Listeria can contaminate some low-acid ferments and cheeses. [2]
Is kombucha safe?
The only systematic review we found is from 2003 and found no clinical evidence of benefit and some safety case reports. [8] See Kombucha for more.
Who should avoid fermented foods?
The sources we read do not tell any group to avoid all fermented foods, but pregnant people, older adults and people with weak immune systems are at higher risk from Listeria, [9] and should ask a clinician.
Do fermented foods cause food poisoning?
Rarely when properly made, according to an expert panel. [2] Contamination is the exception, not the rule.
References
- MedlinePlus (US National Library of Medicine). Botulism. Read 2026-10-23.
- Marco ML et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol 2021. PMID 33398112; full text read at PMC7925329. Read 2026-10-23.
- Guzel M et al. Health benefits of fermented foods: a strategic roadmap from the PIMENTO initiative. Front Nutr 2026. PMID 42827539. Read 2026-10-23.
- Skowron K et al. Two Faces of Fermented Foods: The Benefits and Threats of Its Consumption. Front Microbiol 2022. PMID 35330774 (abstract read). Read 2026-10-23.
- Centers for Disease Control and Prevention. Foodborne botulism from home-prepared fermented tofu, California, 2006. MMWR 2007;56:96-7. PMID 17287713 (abstract read). Read 2026-10-23.
- National Center for Home Food Preservation (University of Georgia, USDA-funded). General Information on Fermenting. Read 2026-10-23.
- National Center for Home Food Preservation (University of Georgia, USDA-funded). Kombucha Tea (tested home method, page read for its caution only). Read 2026-10-23.
- Ernst E. Kombucha: a systematic review of the clinical evidence. Forsch Komplementarmed Klass Naturheilkd 2003. PMID 12808367 (abstract read; an older review). Read 2026-10-23.
- MedlinePlus (US National Library of Medicine). Listeria Infections. Read 2026-10-23.
- US Food and Drug Administration. Listeria (Listeriosis). Read 2026-10-23.
- National Center for Complementary and Integrative Health (US). Probiotics: Usefulness and Safety. Read 2026-10-23.