It’s been a whirlwind 12 months for Texas-based Blue Bell Creameries. This time last year, the frozen treats company was linked to a Listeria outbreak which resulted in a recall of all company products. After a crucial investment got the brand back on track, a well-executed five-phase market reentry plan slowly got product back on store shelves.

While the work at rebuilding is far from over, two root cause assessment reports written by Blue Bell and released by FDA last week offer a better picture of what went wrong. At Blue Bell’s Oklahoma plant, cleaned equipment stored outside the sanitary production area was possibly contaminated because of its proximity to a nearby drain. “We learned it was possible for particles potentially carrying Listeria to be emitted from this drain,” Blue Bell says. “The drains from the facility ultimately empty into the same system to which this drain was connected, creating the potential for Listeria in the plant environment to be washed into the drains to be re-released into the storage room. We believe that this mechanism—particles emitted from a drain—was the most likely source of Listeria.”