10/29/2026
A caramel apple seemed like one of the least likely places for Listeria to grow. Then a 2014–2015 outbreak sickened 35 people in 12 U.S. states, and investigators traced it to apples from one California grower. Later lab experiments suggested that inserting a stick could release juice beneath the caramel and create a moist pocket where Listeria could grow. This is the story of what the outbreak investigation found, what the experiments added, and how a thin layer between two foods can become its own environment.