Hands up anyone who, at any time during their lifetime, has scraped the cake mixing bowl and eaten the residues, or eaten raw cookie dough. Yes, I see a lot of you with your hands up! In a survey by Ardent Mills, Minnesota, 73% of respondents admitted to eating raw homemade cookie dough and 57% allowed children to lick the bowl and spoon after mixing cakes, while 65% admitted to eating store-bought cookie dough without cooking. In a 2009 outbreak of Escherichia coli O157 food poisoning in 30 U.S. states, 77 patients, mostly young females contracted the illness and 35 were hospitalised. A common factor revealed in the investigation was consumption of commercial raw cookie dough produced in a single plant. As a result, 3.6 million packages of ready-to-bake cookie dough were recalled.
I used to beg my Mum not to use a spatula to scrape all the mixture from the bowl. Mum didn’t know much about food safety; she had no formal training and over the years had learned how to bake. Many younger people are probably in the same boat. Most of us know that you can possibly pick up Salmonella food poisoning from eating undercooked eggs or chicken, and that the foods likely to give you food poisoning include leafy greens and sprouts, raw shellfish and raw milk, though the latter usually ignites a flame war if you publish comments.
So if you are asked why you should not eat raw cookie dough, what will you say is the risk? Salmonella in the uncooked eggs, right? What about the flour? In 2016, ten million pounds of raw flour were recalled owing to contamination with Escherichia coli. That year, the U.S. FDA and Centres for Disease Control and Prevention investigated infections by E.coli O121 occurring across the country. Some serotypes of this bacterium can produce Shiga toxins. A great deal is now known about Shiga toxins, but for our purposes here, we can say that ingestion of the toxin results in abdominal pain and watery diarrhoea, but may also cause haemorrhagic colitis, which is far more serious.
The April 23 edition of Morbidity and Mortality Weekly Report discussed multi-state outbreaks of E. coli O26:H11 infections linked to raw flour in 2019. The investigators initially thought that ground beef was the source of the infection - patients interviewed reported eating ground beef and leafy greens. However, by the use of modern microbiological analytical techniques - Pulsed Field Gel Electrophoresis and Core Genome Multilocus Sequence Typing - they were able to show that the STEC O26:H11 isolates were different from those strains that had caused the ground beef illnesses in 2018.
How does flour, which is dry and doesn’t support bacterial growth, come to be involved in E. coli food poisoning transmitted in raw cookie dough? Wheat flour is grown outdoors and may be contaminated from soil or birds and animals. Cattle and deer have no cell receptors for Shiga toxin, so may carry the toxigenic bacteria without ill effect. The milling process generally doesn’t include a lethal process step, so E. coli and Salmonella can survive into the finished product. These vegetative cells are killed during cooking, but may be present in raw dough and cake batter.
Heat treatment of flour has been used in the past to destroy pathogens, but is expensive and has a negative impact on the properties of gluten, potentially making the flour unsuitable for baking. Various other treatments have been proposed, including cold plasma, electron beam and gamma irradiation, but these methods may meet with consumer resistance.
A company based in Ontario, Canada has recently developed an organic, non-thermal treatment for flour that is a liquid added at the tempering stage of milling. However, as far as I am aware, this treatment is not yet used in commercial flour production.
What about making home-made raw cookie dough safe? It is extraordinarily difficult to find information on how to pasteurise raw flour at home to make raw cookie dough treats. One blogger has described home pasteurisation of flour, using a 1200 watt microwave oven to heat the flour to 71C with a 55 second treatment. She based this treatment on advice from FDA and I estimate that the flour receives an F0 of around 4.
FDA is now pushing the message “Don’t eat any raw cookie dough, cake mix, batter, or any other raw dough or batter product that is supposed to be cooked or baked” and “Follow package directions for cooking products containing flour at proper temperatures and for specified times”.
Indeed, some packages of flour in US now have a label warning consumers to “Cook before sneaking a taste”.
Still want to risk it?