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Deep frozen berries are better thoroughly cooked before consumption

05/2013, 13.03.2013

Deep frozen berries are better thoroughly cooked before consumption

The high responsibility that comes with catering in community institutions was underscored by a case of acute diarrhoea with vomiting in kindergarten and school children in 2012. A total of almost 11,000 cases of illness were reported as part of what has so far been the largest food-borne outbreak of gastroenteritis in Germany. According to the finding of the investigations conducted by the federal government and the federal states, deep-frozen strawberries of a specific batch contaminated with norovirus caused the outbreak. The berries had been prepared for consumption in various industrial kitchens. “This outbreak has shown that the consumption of deep-frozen berries can make you ill, if they are not or only insufficiently heated before they are eaten”, says Professor Dr. Dr. Andreas Hensel, President of the Federal Institute for Risk Assessment (BfR). The BfR has therefore updated its leaflet “Safe Food” including recommendations for certain institutional catering facilities in order to draw attention to the issue.

Data published in recent years show clearly that norovirus occur on deep-frozen berries and that they can cause outbreaks of illness. Laboratory detection of norovirus in the batch of deep-frozen strawberries that caused the outbreak in autumn 2012 has now also confirmed this insight for Germany.

Berries can come into contact with norovirus at different points of their production, for example through improper irrigation or fertilisation. In addition, persons infected with norovirus can spread the virus to the berries during the harvest or packaging. In the case of deep-frozen berries, norovirus also comes into contact with the berries through contaminated water which is added as part of the freezing process.

Noroviruses cause acute diarrhoea with vomiting in humans of all age groups, with the illness leading to a considerable loss of fluids. For babies and young children as well as old and ill persons, the illness can be severe and end in death in some cases.

According to the current state of knowledge, it is to be assumed that a high risk of infection is posed not only by raw but also by briefly or unevenly heated dishes made from deep-frozen berries, if they are contaminated with norovirus. However, heating to a core temperature of over 90 °C seems sufficient to completely inactivate any viruses that may be present.

In consequence, the BfR has updated its leaflet “Safe food: especially vulnerable groups in community institutions” and recommends to refrain from serving deep-frozen berries to especially sensitive groups of persons in community institutions without sufficiently heating them beforehand. The target group of this leaflet are employees responsible for the catering services provided in such institutions. The information provided by the BfR is to help them comply with the legal requirements.

The updated leaflet can be downloaded free of charge from the homepage of the BfR where it can also be ordered via the shopping cart function: 

About the BfR

The Federal Institute for Risk Assessment (BfR) is a scientific institution within the portfolio of the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV). It advises the Federal Government and Federal Laender on questions of food, chemical and product safety. The BfR conducts its own research on topics that are closely linked to its assessment tasks.


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Safe Food - Especially Vulnerable Groups in Community Institutions 718.6 KB


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