January 12, 2024, 3:25 pm | Read time: 3 minutes
Serving drinks is standard on most flights. But did you know there’s one drink request that flight attendants particularly dislike? It’s neither the famously popular tomato juice at high altitudes nor coffee or alcohol.
Coffee, tea, water, various juices, sodas, and sometimes beer, wine, and spirits: Passengers have a wide range of drinks to choose from on a plane. However, there’s one order that makes flight attendants roll their eyes internally: “A Diet Coke, please.” TRAVELBOOK reveals why this is the case.
Why Diet Coke Is Problematic on Planes
The reason: The carbonated soft drink foams excessively, significantly prolonging the pouring process. “It takes forever to fill a glass,” confirms a German flight attendant working for a major airline, when asked by TRAVELBOOK. “In the same time, I could have poured two to three other drinks like coffee, tea, or juice.” Another flight attendant has also noticed that the Coke foams even more when there are ice cubes in the glass. “But if I pour the Coke first and add the ice afterward, it foams less, so I always do it that way.”
But why does diet cola with sweeteners foam more than other carbonated drinks? Dr. Ulrich Krings from the Institute of Food Chemistry at the University of Hannover explains: “Perhaps the amount of CO₂ in this type of cola is simply higher. It could also be due to the type of acid contained in the drink.”
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Low Pressure Promotes Foaming
The fact that Coke foams more on a plane is also due to the reduced air pressure in the cabin. “Low pressure facilitates degassing,” explains food chemist Krings. Additionally, it’s possible that the drinks are not as cold when served on a plane, which also promotes bubble formation. “The rocking of the drinks on the serving cart can also promote stronger foaming,” says Krings. The reason: The movement disrupts the equilibrium between pressure and gas solubility.
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Other Drinks Also Foam Strongly on Planes
Due to the reduced air pressure and other factors, not only does Diet Coke foam more on planes, but other carbonated drinks do as well. “With champagne, it can also take longer as it foams very strongly,” the flight attendant tells TRAVELBOOK. Her trick to avoid wasting time: “I just serve the next guest and then continue pouring the champagne.”