The Omaha-based company conducted a nearly two-month investigation into the contamination and pledged to ensure that Peter Pan peanut butter is safe when it returns to stores in mid-July.
"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 problems at 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 events mixed with dormant salmonella bacteria in the plant that Childs said likely came from raw peanuts and peanut dust.
The plant was cleaned thoroughly after the roof leak and sprinkler problem, but the salmonella remained and somehow came in contact with peanut butter before it was packaged, she said.
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 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.
Peanuts grow underground and salmonella is present in the dirt, but generally any bacteria are killed when the nuts 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 salmonella would be most likely to contaminate peanut butter as it cooled and was placed in jars. At most plants, those steps take just minutes.
The company plans to redesign the plant to provide greater separation between raw peanuts and the finished product, Childs said. The plant will also get a new roof.
ConAgra plans to reopen the plant in early August.
Before this recall, none of ConAgra's recent routine testing had detected salmonella, so the company plans to develop a new procedure.
The Food and Drug Administration inspected the plant in February 2005 and found no problems, agency spokesman Michael Herndon has said. He did not immediately return calls Thursday. ConAgra has hired an experienced microbiologist to oversee food safety, Childs said. While renovations are being done, Peter Pan will be made at another company's plant, the company said. Childs declined to identify that manufacturing partner and said ConAgra had not decided whether that plant will continue making Peter Pan after its Sylvester factory reopens. Since the recall shut down production, the Sylvester plant's roughly 100 workers have been paid to do maintenance work. Childs said it's not yet clear how the renovations will affect those employees. Before the recall, ConAgra sold $150 million worth of peanut butter each year, Childs said. In addition to peanut butter, the company's brand names include Healthy Choice, Chef Boyardee and Orville Redenbacher. Salmonella sickens about 40,000 people a year in the U.S. and kills about 600. It can cause diarrhea, fever, dehydration, abdominal pain and vomiting. But most cases of salmonella poisoning are caused by undercooked eggs and chicken. The only previously known salmonella outbreak in peanut butter - in Australia during the mid-1990s - was blamed on unsanitary plant conditions.