Study shows why listeria flourishes on some caramel apples

Unless you have braces or hate delicious things, caramel apples are likely one of your favorite fall treats, but a new study suggests that danger can lurk under that sweet, sticky surface.

Researchers wrote in the journal mBio that it's easier for caramel apples to become contaminated with listeria when they're put on a stick and stored at room temperature, Time reports. The team coated Granny Smith apples with four listeria strains involved in a deadly 2014 listeria outbreak linked to caramel apples, puncturing half of the apples with sticks and dipping all of them in caramel. The researchers stored the caramel apples in either a fridge at 44.6 degrees Fahrenheit, or at 77 degrees Fahrenheit (around room temperature) for four weeks.

The team found that listeria growth seemed to be linked to both the temperature and sticks — refrigerated apples without sticks did not have any listeria growth, while caramel apples that had been punctured and stored at 77 degrees had bacteria that increased 1,000-fold in three days. Apples stored at 77 degrees without sticks had bacteria growth at a slower rate, and apples refrigerated with sticks didn't have any listeria growth over the first week, but had some growth after. The team said that because the sticks caused apple juice to be released into the caramel coating, it was the right environment for bacteria to flourish, and they hope the research can be used by manufacturers to keep bacterial growth at bay.

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