How can pasteurised ice-cream contain Listeria?

In the US, there has been 16 different Listeria-related recalls in just two months, including products like hummus, frozen spinach, smoothie kits and, notably, ice-cream. A food safety specialist has explained how ice-cream could be contaminated.

“Listeria is a group of bacteria that is found in cold, wet environments,” said Fadi Aramouni, extension specialist and professor of food science at Kansas State University. “What’s unusual about this type of bacterium is they actually grow and multiply under refrigerated conditions.”

Listeria is typically found in ready-to-eat deli meats and hot dogs, refrigerated meat spreads, unpasteurised milk and dairy products, soft cheese made with unpasteurised milk, refrigerated smoked seafood and raw sprouts.

“A Listeria contamination in ice-cream hasn’t happened for a very long time because the pasteurisation process kills the pathogen,” Aramouni said. “However, Listeria may survive in the environment if there are not good sanitation procedures in place. Because it survives in cold, wet environments, it can be found in drains or other areas of condensation within a plant, such as the ceiling or light fixtures.”

He says the Listeria in ice-cream also could be coming from the added ingredients.

“One of the things people may not know about ice-cream is that it is not pasteurised after the inclusions are put in,” he said. “After they pasteurise the milk and make the ice-cream, they add things like cookie dough or pecans. The ice-cream is then placed in the freezer and does not go through any other type of pasteurisation, so if the additional products are contaminated, Listeria may survive that process.”

While Listeria is relatively benign in healthy people, it can be deadly for those at risk, including pregnant women, young children, the elderly and people with weakened immune systems

“About 75% of these [at risk] individuals who get listeriosis end up in the hospital and about 25% of them die, so it is quite virulent for this group,” said Aramouni. “Don’t take chances. Any time there’s a recall, respect that recall and do not consume the food.”