"Consumer safety and health is our top priority," ConAgra spokeswoman Stephanie Childs said. "We plan to do our best to regain consumer trust once Peter Pan returns to stores."
Childs said the company traced the salmonella outbreak to three incidents in its Sylvester, Ga., plant last August.
The plant's roof leaked during a rainstorm and the sprinkler system went off twice because of a faulty sprinkler, which was repaired.
The moisture from those three incidents mixed with dormant salmonella bacteria in the plant that Childs said likely came from raw peanuts and peanut dust.
She said the plant was cleaned thoroughly after the roof leak and sprinkler incidents, but somehow the salmonella remained and came in contact with peanut butter before it was packaged.
ConAgra recalled all its peanut butter in February after federal health officials linked it to cases of salmonella infection. At least 425 people in 44 states were sickened, and numerous lawsuits have been filed against the company.
The recall covered all Peter Pan peanut butter and all Great Value peanut butter made at the Sylvester plant since October 2004. That plant is ConAgra's only peanut butter plant.
The company isn't sure exactly how the salmonella got into the peanut butter, but Childs said it was linked to the moisture.
"At some point, the salmonella that was activated came in contact with finished peanut butter," Childs said.
Peanuts grow underground and salmonella is present in the dirt, but generally any bacteria are killed when raw peanuts are roasted. When making peanut butter, the nuts are again heated - above the salmonella-killing temperature of 165 degrees - as they are ground into a paste and mixed with other ingredients before being squirted into jars and quickly sealed.
Experts had speculated that the point in the process where salmonella could be introduced and survive would be as the product cools down, is placed in the jars and then sealed. At most plants, those steps take just minutes.
The company plans to redesign the layout of the Sylvester plant, so there will be greater separation between raw peanuts and the finished product, Childs said. And the plant will receive a new roof.
ConAgra also will develop a new testing procedure for peanut butter, and the company has recruited Mike Doyle, director of the University of Georgia's Center for Food Safety, to lead an advisory committee that will help ConAgra improve procedures at all its plants.
In addition to peanut butter, ConAgra has many brand-name lines, such as Healthy Choice, Chef Boyardee and Orville Redenbacher.
ConAgra plans to reopen its Sylvester plant in early August, but the details of the renovations there are still being finalized.
The Sylvester plant's roughly 100 workers have been paid to do maintenance work since the recall shut down production there. Childs said it's not yet clear how the renovations will affect those workers.
Childs said she didn't know how much the changes at the plant would cost, but the renovation costs would be in addition to the $50 million to $60 million cost of the recall company officials had already announced.
While renovations are being done in Sylvester, Childs said Peter Pan would be made at another company's manufacturing plant. She declined to identify that manufacturing partner and said ConAgra had not decided whether that plant will continue making Peter Pan after its Sylvester plant reopens.
Childs said ConAgra made sure the other company's plant met its safety and quality standards.
ConAgra hopes its peanut butter will return to pre-recall levels of about $150 million in annual sales, Childs said. .