Food & Diet

How Caramel Apples Develop Listeria, Uncovered

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In 2014 there was a listeria breakout which killed 7 people and made 35 sick. Researchers investigated the issue in order to find the food causing the spread of this bacteria and the sickening of people, and they found that listeria was coming from caramel apples.

The researchers at the Food Research Institute at the University of Wisconsin were surprised with their findings, as caramel apples usually don’t typically contain the bacteria, and neither do fresh apples.


Apples became a ‘fertile ground’ for these bacteria to grow because the sticks were inserted into the apples before they were dipped into the caramel and thus there was enough space between the caramel and the apple’s skin for the bacteria.


The symptoms these bacteria cause commonly include abdominal pain, body fever and chills, as well as diarrhea. The bad news is that keeping caramel apples in the refrigerator won’t prevent the bacteria from growing, as they can grow in cold areas as well (but at a decreased speed). The longer these apples stay on the shelf or in the fridge, the bigger the chances are that there will be an infestation of these bacteria which will lead to these highly unpleasant symptoms.

As Kathleen Glass, associate director at the Food Research Institute, said in a press release, eating those apples fresh before they were dipped into caramel would probably not lead to negative consequences, but as caramel apples are usually left on a shelf at room temperature for several days and even up to two weeks, the bacteria have enough time to grow and spread, making those delicious caramel apples very dangerous for consumption. When buying them, the worst thing is that there’s no way of knowing just how fresh those caramel apples are. They could be standing there on the shelf for more than a week.


Research Methodology

During the research, two groups of apples were tested, one group with a stick inserted into the apples’ cores before cooling down, and the other without a stick. The sticks were inserted before the apples were dipped into caramel, and then all apples were exposed to listeria. Both groups were then refrigerated, some at 44.6o F and some at 77o F for around a month in order to see how temperature and time affect the growth of listeria in these apples.

The researchers supposed that apples release some juice onto the surface when a stick is inserted into the apples’ cores. This juice is then practically trapped between the fruit’s skin and the caramel, which provides a perfect place for bacteria to grow.


In both groups (cooled down at 44,6o F and 77o F), the apples with sticks inserted into them had higher levels of listeria than those that were dipped into caramel and cooled down without a stick being inserted into them. Moreover, from the two groups of apples that were kept at 77o F, listeria levels were considerably higher in those which had sticks inside than those that didn’t.

The apples kept at 44.6o F with sticks inside them had lower levels of listeria than the same apples that were stored at 77o F. The apples that didn’t have sticks inserted were kept in the refrigerator for 28 days and they still didn’t have listeria growing.

Having this in mind, you should carefully consider all the factors before buying caramel apples ever again.

Glass explains that washing the apples well before dipping them in caramel could inhibit the growth of listeria. If you’re sure that the vendor you’re buying from sells many of these apples daily, and washes them well or adds a growth inhibitor to prevent listeria, feel free to enjoy these delicious sweets.

ALWAYS AVOID vendors whose apples may have been standing for weeks