Where Deadly Peanut Butter Comes From

The Food and Drug Administration confirmed Wednesday that the salmonella outbreak that has killed several people and sickened nearly 500 in 43 states has been traced to Peanut Corp. of America's Blakely, Ga., plant and did not occur further along the supply chain.

Further pinpointing the cause will be that much easier, thanks to the fact that roasting peanuts almost certainly kills any bacteria, so the contamination probably came after the peanuts were roasted but before processing was finished.

Officials are now investigating precisely how it happened, but the answer, sorry to say, is probably going to involve animal feces. Over the past 15 years, there have been only two salmonella outbreaks involving peanuts. One of them, according to Scientific American, was caused by a leaky roof in a processing plant. The source in that case was probably bird droppings.

Despite its relatively clean past, several factors could be making peanut butter particularly vulnerable to such outbreaks. Processing plants are aging, and leaks are more common. Also, peanut butter, thanks to its high fat content, is a good carrier for the disease: Fat tends to protect the bacteria from harm, including from stomach acids. And since irradiation tends to make fatty, processed foods smell funny, and since heat treatment hasn't proved effective for peanut butter, it's particularly important to adhere to strict safety guidelines during processing, especially when it comes to managing water.

"Water in a peanut butter processing plant is like putting gasoline on a fire," according to Micheal Doyle, director of the Center for Food Safety at the University of Georgia, in an interview with Scientific American. "It will not only spread the salmonella, but the salmonella will grow when water is present."

Salmonella can survive for months in peanut butter—thanks, again, to the product's fat content.