In early 2020 an assessment was realeased by the German Federal Institute for Risk Assessment (BfR), which showed that there was a wide and significant distribution of Shiga toxin-producing E. coli (STEC) in German flour.
123 strains were found in flour products between 2015 and 2019 across the country. Wheat flour had the highest quantity of isolates with rye flour second. It was also found that some samples had more than one strain of E.coli.
The study was published in the International Journal of Food Microbiology.
The strains were found in multiple locations so the contamination could not have been a single source.
A possible explanation for the contamination may be wild animals or maybe the water used during processing or cleaning.
One thing is certain, that based on this study, flour cannot be considered to not be a food safety issue, even though it is low moisture ingredient.
The study reinforces the advice provided by food safety authorities across the world, that uncooked flour in products like cake batter or cookie dough should not be eaten.