The sticky truth about caramel apples and Listeria

CaramelApples_blogAlong with haunted houses and scary movies, caramel apples are a staple during the fall season for children and adults alike. However, the sweet and sticky treat can have a dark side, according to a new study published in the journal mBio, which showed that caramel apples stored at room temperature can more quickly become contaminated with Listeria.

As witnessed for first time in 2014, an outbreak of Listeria later linked to caramel apples resulted in seven deaths and 35 illness throughout several states. In the new study, researchers chose four of the Listeria strains involved in the outbreak and coated them on Granny Smith apples. They then punctured half of the apples with sticks and dipped all of them in caramel. For four weeks, the apples were either stored at 77°F (around room temperature) or in a refrigerator at 44.6°F.

Food-safety experts say Listeria can be particularly tricky and virulent pathogen because it can blossom in refrigerated environments, unlike other foodborne pathogens.

According to an article detailing the study, both the temperatures and sticks seemed to play a role in Listeria growth. For example, the researchers found that the refrigerated apples without sticks had no Listeria growth at all, while the caramel apples with sticks stored at room temperature had bacteria that increased 1,000-fold in just three days.

Apples without sticks stored at the same temperature had bacteria growth, but at a slower pace. The apples that were refrigerated with sticks had no Listeria growth for the first week, but they had some growth over the next few weeks.

In conclusion, the researchers found that piercing a caramel apple with a stick causes some juice to become trapped under the caramel, creating an environment that aids the growth of Listeria already present on the apple’s surface.

The study authors suggest that their findings can help inform caramel apple manufacturers of best practices to avoid bacterial growth and caramel apple fans should keep an eye out for fresh versions—or at least the refrigerated kind, the article states.

Since the study was published, some grocery store chains have already removed their unrefrigerated caramel apples and said they will take the necessary precautions for storing caramel apples in the future.

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