Nutrition and Food Safety: Understanding What Bacteria Grows in Peanut Butter?

October 4, 2025 •

4 min read

While peanut butter is a shelf-stable food due to its low moisture content, the Centers for Disease Control and Prevention (CDC) estimates that Salmonella infects 1.35 million people annually, and several high-profile outbreaks have been traced to contaminated peanut butter. Understanding what bacteria grows in peanut butter is crucial for mitigating health risks, particularly the survival of hardy pathogens rather than active growth.

Quick Summary

Low water activity in peanut butter generally prevents bacteria from growing, but pathogens like Salmonella can survive for long periods and cause illness if introduced through post-roasting contamination. Factors like product formulation and storage temperature can influence pathogen survival. Maintaining proper hygiene and storage practices is key to minimizing health risks.

Key Points

Survival, Not Growth: Peanut butter's low water activity prevents bacteria from multiplying, but pathogens like Salmonella can survive for long periods.
Salmonella is the Main Risk: Contamination with Salmonella, often from processing facilities, is the most common peanut butter-related food safety issue.
Post-Roasting Contamination: The high-heat roasting process kills bacteria, but re-contamination can occur afterward if equipment or facilities are not properly sanitized.
Infant Botulism Risk: Spores of Clostridium botulinum can be present, making peanut butter unsafe for infants under 12 months old.
Clean Utensils are Key: Use a clean utensil each time to prevent introducing bacteria from other food items into the jar.
Proper Storage Matters: Store conventional peanut butter in a cool, dry place and natural varieties in the refrigerator to maximize freshness and safety.
Fat Protects Pathogens: The high fat content of peanut butter provides a protective environment that helps pathogens like Salmonella survive for longer.

Understanding Microbial Survival in Low-Moisture Foods

Peanut butter's safety profile is unique because it is classified as a low-moisture food, with a water activity (aw) typically below 0.85. This low water content is the primary reason why bacteria cannot actively multiply or grow in peanut butter. However, this does not mean it is entirely free from microbial risk. Instead of active growth, the concern centers on the survival of resilient foodborne pathogens that can persist in this dry environment for extended periods, sometimes for the product's entire shelf life.

The Most Concerning Contaminant: Salmonella

Among the bacteria that can survive in peanut butter, Salmonella is the most significant and well-documented concern. This robust pathogen is capable of withstanding the desiccating conditions of low-moisture foods and has been responsible for numerous recalls and foodborne illness outbreaks linked to peanut butter.

Source of contamination: While the high heat used during the peanut roasting process effectively kills most pathogens, contamination can occur afterward. Environmental sources in the processing facility, such as contaminated equipment, surfaces, or even dust, can introduce Salmonella to the finished product before it is jarred. Peanuts grown in the ground are also exposed to environmental sources of bacteria.
Mechanism of survival: In the low-moisture environment, Salmonella does not multiply but enters a highly resistant state. The high fat content of peanut butter is believed to offer a protective shield, enhancing the bacteria's survival and heat resistance. Research has shown that some strains of Salmonella can survive in peanut butter for many months, making contamination a persistent threat.

Other Potential Bacterial Concerns

Although less common than Salmonella outbreaks, other pathogenic bacteria have been associated with nut products and low-moisture foods. While they do not thrive in peanut butter, they can potentially survive and pose a risk.

Clostridium botulinum: This bacterium, known for causing infant botulism, can produce heat-resistant spores. Infants under one year should never be given honey or peanut butter that could contain these spores. A 2025 UK infant botulism case was traced to a contaminated jar of commercially prepared peanut butter.
Listeria monocytogenes: Similar to Salmonella, Listeria is known to survive for long periods in dry environments. Studies have shown its ability to persist in peanut butter, and it has prompted recalls in the past, though no illnesses were reported in those specific instances.
E. coli O157:H7: Certain strains of E. coli have also shown resistance in low-moisture foods, especially those with high sugar content.

Minimizing Your Risk of Contamination

For consumers, following proper handling and storage practices is the best line of defense against microbial contamination in peanut butter. Here are some key recommendations:

Use clean utensils: Never double-dip or use a utensil that has touched other foods, like jam or breadcrumbs, to prevent cross-contamination.
Seal the jar tightly: After each use, securely fasten the lid to minimize exposure to air and moisture, which can accelerate rancidity and spoilage.
Store in a cool, dry place: For conventional, shelf-stable peanut butter, a pantry is sufficient. For natural peanut butters without stabilizers, refrigeration is recommended to preserve freshness and slow oil separation.
Refrigerate natural peanut butter: Natural peanut butter has a shorter shelf life and is more susceptible to mold growth due to the lack of preservatives. Refrigerating it after opening is the best practice.

Comparison of Bacterial Growth vs. Survival in Peanut Butter


Feature	Active Bacterial Growth (in ideal conditions)	Bacterial Survival (in peanut butter)
Moisture Content	Requires high water activity (>0.85)	Occurs in low water activity (<0.85)
Population Change	Increases exponentially over time	Remains stable or decreases slowly over time
Metabolic State	Metabolically active and replicating	Enters a dormant, resilient state
Protection	Little to no matrix-based protection	High fat content provides a protective barrier against external stressors like heat and dryness
Duration	Hours to days	Many weeks, months, or even years

Conclusion: Prioritizing Safe Handling for a Nutritious Diet

Peanut butter remains a staple in a nutritious diet, providing a good source of protein and healthy fats. However, its low-moisture environment, while preventing bacterial growth, can allow pathogens like Salmonella to survive for extended periods if contamination occurs during processing. The risk of foodborne illness is largely mitigated by robust food safety protocols in manufacturing facilities and sound handling practices by the consumer. By using clean utensils and storing peanut butter properly, you can enjoy this versatile food without compromising your health.

This article was produced for informational purposes and is not a substitute for professional food safety advice. For specific health concerns, consult a healthcare provider. For more information on proper food storage, visit the U.S. Food and Drug Administration website.

Frequently Asked Questions

No, bacteria cannot actively grow or multiply in peanut butter because it is a low-moisture food with a very low water activity level. However, hardy pathogens like Salmonella can survive in it for extended periods.

Contamination typically occurs after the roasting stage during processing. Poor hygiene, unsanitized equipment, or environmental factors like contaminated dust or moisture in the processing facility can introduce bacteria.

Salmonella is a foodborne pathogen known for its ability to survive in dry environments. In peanut butter, its survival is enhanced by the high fat content, allowing it to persist for months and cause illness if consumed.

Peanut butter can be a vector for Clostridium botulinum spores, which can cause infant botulism. For this reason, and because of other choking hazards, experts advise against giving honey and potentially contaminated foods to infants under one year of age.

Store conventional peanut butter in a cool, dry pantry after opening. For natural peanut butter, refrigeration is recommended to preserve freshness and prevent mold or rancidity, although it may become harder.

Yes, cross-contamination is a risk if you use an unclean utensil to scoop peanut butter, especially one that has been used with high-moisture foods like jam. This can introduce bacteria that could then survive in the jar.

The shelf life varies by type. An opened jar of conventional peanut butter can last about 2-3 months in the pantry and longer in the fridge. Opened natural peanut butter is best consumed within 3-4 months if refrigerated.