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The Unsettling Truth About Blowing Out Candles on Cake

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“Bacterial Transfer Associated with Blowing Out Candles on a Birthday Cake,” reads the title of a recent study out of the Journal of Food Research. That’s quite a headline! The study presented a somewhat unsurprising finding: Saliva travels, so, naturally, the seemingly benign act of blowing out candles on a birthday cake involves the transmission of bacteria.

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To determine how much, exactly, bacteria gets transferred in this process, the researchers from Clemson University constructed a mock cake and simulated a meal-dessert sequence with their 11 test subjects, replicated 3 times on separate days. Their methodology involved taking a sheet of foil and cutting it in the shape of a circle, placing that foil on a Styrofoam disk, and enveloping it in a thin layer of Betty Crocker's Rich & Creamy Vanilla frosting. The researchers then planted 17 candles, evenly spaced, into the Styrofoam, careful to permeate both the icing and foil layers.

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Each subject then smelled and consumed a slice of hot, piping pizza, meant to emulate a meal-dessert sequence. After lighting the candles on the mock cake, researchers asked subjects to blow until they doused the tiny flames. This was followed, of course, by a control scenario, which replicated the procedure except for the final step: The candles weren’t blown out.

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Following each scenario, the researchers removed the candles from the Styrofoam bases without touching the icing. Using sterile forceps, they placed the folded foil in stomacher bags, pouring a bit of sterile peptone solution into the bags. They then spread the resultant solution on agar plates, where bacteria could blossom.

The findings, ultimately, were that blowing out candles resulted in a whopping 15 times more the amount of bacteria, on average, recovered from the icing compared to the control samples. This number obviously varied from trial to trial and subject to subject; in one person's case, this number was as high as 120 times more.

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None of this is terribly shocking. I don’t think the researchers quite mean to cause alarm, nor do they intend for this to give rise to the same germaphobic anxiety that's ruined bobbing for apples, double dipping, or sharing straws. “Bacterias are an unavoidable part of life, present in and on almost everything humans contact,” it concludes. No kidding!

What I find more interesting about this study is the potential it’s opening up for innovators to make this gesture germ-proof. These findings, the researchers hope, will simply arm people with more “awareness" of possible health risks associated with birthday celebrations, and prompt people to take steps toward preventing the spread of bacteria. There are signs that it's happening: The Atlantic's Sarah Zhang found a 9-year-old patent floating around out there for a sanitary birthday cake and candle cover system. Perhaps you may consider such a contraption totally unnecessary. But if it takes a cover system to ease people’s fears while preserving the pleasure of this ritual, so be it.

Read the study in full here. Do you blow out the candles on cakes? Let us know in the comments.

Tags: birthday cakes