Research – How Does Peanut Butter Get Contaminated With Salmonella, Anyway?


Manufacturing Issues May Lead to Salmonella in Peanut Butter

To understand the link between peanut butter and Salmonella, it’s important to go over how peanut butter is made. The process of making peanut butter starts with raw, shelled peanuts that are roasted and cooled, Vijaya Surampudi, MD, clinical nutrition specialist at UCLA Health, told Health. The peanuts are then ground, and heated again during the grinding, she added.

Heating the peanuts and keeping them dry is a hugely important step in keeping your peanut butter safe from contamination, Darin Detwiler, LPD, a professor of food policy and corporate social responsibility at Northeastern University and author of Food Safety: Past, Present, and Predictions, told Health.

“Peanut butter is made from shelled and ground peanuts that are typically left sitting in unprotected piles until ready for the next stage of food manufacturing or for delivery to another company,” said Detwiler. “Most cases of Salmonella in peanuts are caused by the presence of rain water bringing feces onto the product, or animals—birds, or more likely rodents—[coming] directly] into contact with the product.”

Roasting the contaminated peanuts can help kill the Salmonella “if the food is heated to a high enough temperature, held at that temperature for enough time, and cooked throughout,” said Detwiler. But then the peanut butter has to keep that sanitized status after heating and grinding. “Roasted peanut butter can become contaminated in the processing plant if proper sanitation protocols are not followed.”

However, in some cases roasting contaminated peanuts can actually cause a type of heat-tolerant bacteria. “That’s why cleaning and sanitizing of the equipment and the facility is so important in addition to ensuring that the facility is well maintained,” Ellen Shumaker, PhD, food safety extension associate at North Carolina State University, told Health.

Peanut Butter Is an Ideal Place for Salmonella to Survive

According to Detwiler, Salmonella may not be able to grow in peanut butter, but it can survive for “many months” if it gets into the product.

“Peanut butter is a low-moisture food, meaning there is not enough available water to support the growth of microbial pathogens like Salmonella,” Abby Snyder, PhD, assistant professor of food science at the Cornell College of Agriculture and Life Sciences, told Health. “However, while Salmonella can’t grow, it can survive for extended periods of time in low-moisture foods like peanut butter.”

The high fat content of peanut butter may even act like a layer of protection for the bacteria, according to Shumaker. She pointed to a 2000 study in the Journal of Applied Microbiology which found that the bacteria could survive for up to 24 weeks in peanut butter jars.

Another large issue: Peanut butter is considered a “ready to eat” food, meaning people typically eat it without cooking it—which then raises the risk of contracting Salmonella, if the jar is contaminated, said Snyder.

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