What's better at this time of year than a large, shiny caramel-covered apple? They're almost as much a part of Halloween as jack-o'-lanterns and goblins.
But, if you're planning on dipping your own apples or buying ready-made, you might want to take a few precautions to prevent a potentially serious illness.
Researchers reporting in the online journal of the American Society of Microbiology found that Granny Smith apples dipped in caramel became a breeding ground for listeria if the apples were made with sticks and stored at room temperature for several days.
Caramel apples are commonly made by inserting a wooden popsicle stick into the stem end of the apple so you can easily hold it while dipping it into warm, melted caramel. Because they can be difficult to bite into when they are chilled, many people simply store the apples at room temperature and eat them over the course of several days.
Scientists at the University of Wisconsin-Madison's Food Research Institute found inserting a stick into the apple caused juice to leak onto the surface of the fruit. That moisture became trapped under the caramel, creating what one of the lead researchers, Kathleen Glass, called a "microenvironment on the surface of the apple that facilitates growth of any Listeria monocytogenes cells that are already present on the apple surface."
Listeria is a type of bacteria that can cause serious illness, even death. Symptoms include fever, headache, stiff neck and gastrointestinal distress, which may not appear for three or four weeks after eating infected foods.
The University of Wisconsin study was prompted by a listeriosis outbreak in 2014 in which 35 people from 12 states were infected and seven people died. All but three of the 31 victims who became ill reported eating commercially produced, prepackaged caramel apples.
Dianna Thomas, a registered dietitian at St. Anthony's Hospital in St. Petersburg, said most people probably aren't aware of the potential for contracting a listeriosis infection from caramel apples.
Younger, healthy adults may become infected and never know it or have just a mild case of diarrhea. But some groups are at risk for serious illness.
"Anyone whose immune system is compromised, such as those with HIV or cancer, are at high risk. So are the elderly, young children and anyone with a chronic health condition. Moms who are breastfeeding should also be careful with fresh produce and unpasteurized dairy products," Thomas said.
According to UW researchers, caramel apples made without sticks took longer to grow listeria when stored at room temperature. Growth of the bacteria was further delayed, by up to four weeks, when the apples were made without sticks and stored in the refrigerator.
To prevent illness, the researchers recommend using tongs to hold the apples for dipping, eating them right after they are made or inserting the stick right before eating, and storing remaining apples in the refrigerator.
Thomas adds this: "People die from (listeria) infections every year and all those deaths are preventable with proper food handling and storage and avoiding unpasteurized dairy products, especially where people in those high-risk populations are concerned."
Contact Irene Maher at firstname.lastname@example.org.