Pathogens in frozen products

Freezing stops growth, but doesn't kill pathogens 

“Viruses such as norovirus and hepatitis A are things you absolutely don't want in your products, because they pose a major health risk to consumers,” begins Jef Nikkelen, Consultant of Food Microbiology at Eurofins Food Safety Solutions. “The problem is that freezing doesn't kill bacteria and viruses, it only stops them multiplying. Once the product is thawed and consumed without heating, the contamination can still cause harm.” 

For some frozen products, such as raw vegetables and meat, a heating step is common in the production chain. But for others, such as soft fruit (raspberries, blackberries, blueberries) and some baked goods (such as frozen dough), this step often only takes place at the consumer's end – or not at all. That increases the risk of food-borne infections. 

“The problem is that freezing doesn't kill bacteria and viruses, it only stops them multiplying.” 

Recent outbreaks demonstrate the risk 

Laura Goossens, Manager Product Compliance at Eurofins Food Safety Solutions, emphasises that this is not a theoretical problem. “We see recall after recall of frozen products due to contamination. In January 2025 there was a recall of frozen blueberries due to a hepatitis A outbreak. Earlier there were reports of contaminated frozen raspberries in Sweden and New Zealand.” 

Bacterial contamination also remains a major risk. “STEC bacteria (Shiga toxin-producing E. coli) are a well-known hazard in frozen products,” continues Nikkelen. “These bacteria cause a significant proportion of bacterial food poisoning cases and can lead to serious complications.”

According to Ernst Kruithof, Food Safety Consultant, attention must also be paid to contamination risks in unexpected products. “Previous research showed that 10% to 30% of all flour in Europe contains STEC bacteria. That means products such as frozen pizzas or frozen dough can also be contaminated if there hasn't been adequate heating during production. In 2022, this insight led to significant adjustments in the risk analyses of retailers and food producers, following a recall of frozen pizzas in France.” 

“STEC bacteria (Shiga toxin-producing E. coli) are a well-known hazard in frozen products. Attention must also be paid to contamination risks in unexpected products.” 

How can producers reduce the risk? 

Food safety starts with a careful risk analysis. “Producers need to look at the origin of their ingredients and apply supplier screening,” states Goossens. “In addition, it's crucial to carry out (or have carried out) the right checks, such as laboratory testing of delivered raw materials and audits at suppliers. An important tool here is the updated Information Sheet 64 from the NVWA. This information sheet provides guidance for managing relevant hazards associated with purchasing food products and raw materials within the framework of HACCP.” 

The role of process validation 

In addition to preventing contamination at the source, it's essential to test the effectiveness of food processing steps. “A producer must be able to demonstrate that their heating process is effective at killing pathogens,” says Nikkelen. “This is especially important for products that consumers still need to prepare themselves, such as frozen pizzas.” 

“It's crucial to critically analyse and validate the recommended preparation method for consumers,” adds Kruithof. “Is oven preparation sufficient to kill pathogens? And is this preparation method communicated clearly enough on the packaging?” 

“It's crucial to critically analyse and validate the recommended preparation method for consumers.” 

In short: food safety requires continuous attention 

“With an integrated approach, you minimise the risk of contamination in frozen products,” advises Kruithof. “With increasing global trade and the complexity of food supply chains, food safety remains a challenge. The recent outbreak underlines that ongoing monitoring and validation remain necessary to protect consumers against serious and unexpected health risks.”