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Salmonella in Peanut Butter: Mitigating the Risk of Contamination

Posted by Rachel Pacella


A primary and widespread problem in food safety is with outbreaks of pathogenic Salmonella in foods. More commonly, pathogenic Salmonella affects raw meats and poultry products because Salmonella is introduced from animal feces. Salmonella in peanut butter or other nut butters is less known but is still a challenge. Salmonella is a major concern in preserved peanut butter because of its ability to survive in the peanut butter for many weeks. How can the food safety industry be more pro-active in preventing Salmonella infection as a result of contaminated peanut butter, and what pro-active measures can be taken to create a better sanitation process?

What is Salmonella?

The genus of Salmonella contains bacteria that are rod-shaped and gram-negative. They are a part of the family Enterobacteriaceae, which contains other familiar pathogen genera and species, such as E. Coli, Klebsiella and Shigella.

Only some of the many serotypes of Salmonella cause the disease Salmonellosis. Salmonellosis is caused by consuming contaminated foods. The two most common species of Salmonella that cause disease in the US are S. typhimurium and S. enteritidis1. Salmonellosis is characterized by symptoms of diarrhea, abdominal cramps, and vomiting. Some severe cases can be fatal, especially for children under 5, the elderly, and people with weakened immune systems.

Salmonella can contaminate foods in many ways. Salmonella can be spread by food handlers that do not wash their hands between food preparation steps, by eating raw or undercooked foods, or by spreading from animal feces to humans2. The most effective way to prevent the spread of Salmonella in a home or by restaurant workers in restaurants is by proper handwashing between touching food and contaminated surfaces. 

Peanut butter and Salmonella pose a particular challenge to food safety because peanut butter is not produce or an animal product, which are known to host Salmonella well. So, how does Salmonella infect peanut butter, and why are nut butters a high threat for Salmonella outbreaks?

How does Salmonella contaminate Peanut Butter?

Most outbreaks occur when a specific species of bacteria meets a food item during the growing process, mainly due to food contamination by animal feces. Most high-risk foods include raw meat, eggs, and farm-grown produce. Peanut butter on its own is not considered a high-risk food. However, most times Salmonella meets peanut butter during the manufacturing process, rather than the growing process.

When peanuts are harvested for peanut butter, they are dug up and roasted at 160 oC, which kills off any potential bacteria. During the manufacturing process, peanuts are usually stored in large containers before they are taken to be ground into nut butter. When they are stored, they are potentially exposed to rainwater and feces from birds. This exposure could be one cause of contamination. Another source of contamination occurs during the manufacturing process when poor sanitation protocols, or not adhering to sanitation protocols all together, are used pre-manufacturing.  

Peanut butter is not the most ideal product for Salmonella to grow in. The moisture content alone in peanut butter cannot sustain the bacteria. It is believed that the high fat content of peanut butter may be the reason that Salmonella is able to survive for many days in peanut butter. The main fatty acid profile of peanut butter has higher amounts of oleic acid, which increases its shelf life 3. Because of this unique chemical composition and the increase in shelf life, once Salmonella is introduced, it can survive up to 24 weeks in preserved peanut butter 4. The number of survival weeks can fluctuate based on the hardiness of the Salmonella strain. 

What Pro-Active measures can we take to mitigate Salmonella in Peanut Butter?

The most effective way to prevent or mitigate Salmonella contamination in nut butters begins with:
  • Proper Hygiene
  • Proper Sanitation
  • Proper Storage

Storage of peanuts after the roasting process is one of the potential sites of Salmonella contamination. Peanuts, after being roasted, are stored in a large warehouse for a period of time before being sent to be grinded into peanut butter. Often, these large containers are kept in warehouses, which are not cleaned or sanitized. The containers are usually open to the air, which also increases the chance of contamination. When the peanuts are moved to the grinding process, all equipment needed in the manufacturing process should be properly washed, sanitized and dried before starting the process.

Because water is mandatory for Salmonella to grow, processing plants need to mitigate the amount of water introduced after roasting. Water can come in contact anywhere, from leaks in the ceilings, to water used for cleaning the area. All water sources could be a cause for concern, especially in dry processing plants.

Large companies that produce a lot of peanut butter cannot always control the water that is around the peanuts post-roasting. The need for a vigorous HACCP plan for a peanut processing plant is crucial when it comes to mitigating the potential sources of contamination. Our BrandGuard® program includes periodic reviews including sanitation program assessment for peanut and other nut butter processing, for both zones 1 and 2 (equipment) as well as zones 3 and 4 (environmental).

Even if a plant has a HACCP plan for sanitizing and cleaning an area used for peanut butter, the structure of the building where storage and grinding occur, is a cause for concern. Identify areas of the plant that may introduce non-sterile water into storage areas. This could include openings in a ceiling, any leakage of water-based products, or improper cleaning with water. Keep any wet-washing equipment away from the final product or in a separate washing room. 

Salmonella can be introduced during other parts of the process besides the actual product itself. The packaging of the peanut butter (jars, lids, labels) could also pose a risk to introducing bacteria to the product. Items should be stored in a clean and dry area before being used for packaging. The packaging materials and equipment should be cleaned by flushing with filtered (HEPA) air. Vendors should also provide certificates of conformance for the packing materials used. 


1 https://www.medicinenet.com

2 https://www.fda.gov

3 https://www.eurofinsus.com

4 https://pubmed.ncbi.nlm.nih.gov/11021579/


Topics: food safety, food safety audit, food sanitation, food processing allergen, food allergens, nut allergy, allergy testing