This week’s question comes from Stephanie Mencimer of the District who wants to know:
“How much should we worry about getting food poisoning from buttercream frosting made with raw eggs? I took a class on cake decorating…at L’Academie de Cuisine and the instructor told us that the risk was low but also that all the sugar in the icing would inhibit the growth of bacteria. I find this hard to believe. What do you think?”
That’s a great question, and I’d say that even if you weren’t married to Erik Wemple.
According to the American Egg Board, which of course has a vested interest in the discussion, “Scientists estimate that, on average across the U.S., only 1 of every 20,000 eggs might contain the [Salmonella enteritidis or Se] bacteria. So, the likelihood that an egg might contain Se is extremely small—0.005% (five one-thousandths of one percent). At this rate, if you’re an average consumer, you might encounter a contaminated egg once every 84 years.”
Christine Bruhn, director of the Center for Consumer Research at the University of California, Davis, tends to agree with the Egg Board on those stats. But she notes that eggs can also become contaminated from sources far away from the farm—like from your hands (particularly if you separate the yolk from the whites using your dirty, filthy digits) or even from your refrigerator. Bruhn once did a study on how often people wash their fridge, including those little eggs slots on the door. “Most people acknowledged that they just wiped up a spill and they didn’t actually wash the refrigerator very often at all, once a year maybe,” she says.
The problem is, a little bacterium goes a long way. It doesn’t take much to make a person ill, particularly if you’re very young or very old, pregnant or have a compromised immune system. What’s more, bacteria tend to multiply like rabbits jacked up on Viagra, alcohol, and porn. The Egg Board claims that, “If not properly handled, Salmonella bacteria can double every 20 minutes and a single bacterium can multiply into more than a million in 6 hours.”
Sugar, believe it or not, acts as a sort of condom in this bacterial reproduction business. Those sweet crystals tie up the water that bacteria need to multiply. “Sugar is linking, chemically linking, to that water and…keeping it away from the bacteria,” Bruhn says.
Still, Bruhn notes, sugar (like Trojans) are not exactly fail-safe when it comes to prohibiting reproduction. A recipe, she says, needs to be about 80-85 percent sugar to inhibit bacteria growth, and even that won’t guarantee a 100 percent safe frosting, since there may be bacteria already “sitting there alive, just waiting to get you when you eat the product.”
The potential bacteria contamination of buttercream icing is almost impossible to determine, Bruhn says. “It could possibly [have] a high level of sugar that the bacteria would not grow, but it depends on how the person makes it…how moist the cake is, how long it has been sitting around, how hot the room, those various factors.”
In the end, though, the risk of Salmonella poisoning is pretty low, Bruhn admits, unless you’re a member of an at-risk groups. But Bruhn, for one, doesn’t like to take chances. “I would advise those people who are risk-adverse and love the people they cook for just to buy those little cartons of [pasteurized] eggs,” she says. “They can always use the egg white in other dishes like omelets or other cooked dishes later on if they don’t use it all for the frosting.”
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